HIGH-EFFICIENCY GOLD RECOVERY BY ADDITIVE-INDUCED SUPRAMOLECULAR POLYMERIZATION OF CYCLODEXTRIN
20240247336 ยท 2024-07-25
Inventors
Cpc classification
C22B11/025
CHEMISTRY; METALLURGY
C22B5/02
CHEMISTRY; METALLURGY
C22B3/22
CHEMISTRY; METALLURGY
International classification
C22B7/00
CHEMISTRY; METALLURGY
C22B3/22
CHEMISTRY; METALLURGY
C22B5/02
CHEMISTRY; METALLURGY
Abstract
Disclosed herein are composition and methods for gold recover based on precisely controlling the reciprocal transformation and instantaneous assembly of the second-sphere coordinated adducts formed between cyclodextrin and gold anions optionally in the presence of an additive.
Claims
1. An adduct formed from a cyclodextrin, a gold halide anion, and an additive, wherein the gold halide anion occupies a space between primary faces of the cyclodextrin and the additive occupies a space between secondary faces of the cyclodextrin and/or within an internal cavity of the cyclodextrin.
2. The addict of claim 1, wherein cyclodextrin tori are arranged in a head-to-head and tail-to-tail manner extending along an axis and forming a one-dimensional supramolecular polymer.
3. The adduct of claim 1, wherein the gold halide anion is [AuBr.sub.4].sup.? or the cyclodextrin is ?-cyclodextrin.
4. The adduct of claim 1, wherein the gold halide anion is [AuBr.sub.4].sup.? and the cyclodextrin is ?-cyclodextrin.
5. The adduct of claim 1, wherein the additive is hydrophobic and has a binding affinity for the cyclodextrin.
6. The adduct of claim 5, wherein the additive is size-matched to the cavity of the cyclodextrin.
7. The adduct of claim 5, wherein the additive has a boiling point above 50? C.
8. The adduct of claim 5, wherein the additive is selected from an ether, an arene, an alkylarene, a haloalkane, or an alkane.
9. The adduct of claim 5, wherein the additive is selected from dibutyl carbitol, isopropyl ether, benzene, toluene, chloroform, dichloromethane, or hexane.
10. The adduct of claim 5, wherein the additive is dibutyl carbitol.
11. A method for preparing an adduct comprising contacting a cyclodextrin, a gold halide anion, and an additive in solution.
12. The method of claim 11, wherein the additive is added to a solution comprising the cyclodextrin and gold halide anion.
13. The method of claim 12, wherein the additive is added to the solution at a percentage between 0.05% v/v and 5.0% v/v, optionally between 0.05% v/v and 0.5% v/v.
14. The method of claim 12, wherein the molar ratio of cyclodextrin to gold halide anion is between 0.5 and 5.0, optionally between 2.0 and 3.0.
15. The method of claim 12, wherein the concentration of gold halide anion is between 0.01 mM and 5.0 mM, optionally between 0.05 mM and 2.0 mM.
16. The method of claim 12, wherein the additive is added to the solution at a percentage between 0.05% v/v and 5.0% v/v, optionally between 0.05% v/v and 0.5% v/v; wherein the molar ratio of cyclodextrin to gold halide anion is between 0.5 and 5.0, optionally between 2.0 and 3.0; and wherein the concentration of gold halide anion is between 0.01 mM and 5.0 mM, optionally between 0.05 mM and 2.0 mM.
17. A method for recovering gold comprising contacting a gold-bearing material with a hydrogen halide to form a gold halide anion, contacting the gold halide anion with a cyclodextrin and an additive to form an adduct, and reducing the adduct.
18. The method of claim 17, wherein the gold-bearing material is contacted with HBr and H.sub.2O.sub.2.
19. The method of claim 17, wherein the adduct is reduced with N.sub.2H.sub.4.Math.H.sub.2O.
20. The method of claim 17 further comprising recycling the cyclodextrin after reducing the adduct.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
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DETAILED DESCRIPTION OF THE INVENTION
[0035] Developing an eco-friendly, efficient, and highly selective gold-recovery technology is urgently needed in order to maintain sustainable environments and improve the utilization of resources. Here we report a de novo additive-induced gold recovery paradigm based on precisely controlling the reciprocal transformation and instantaneous assembly of the second-sphere coordinated adducts formed between ?-cyclodextrin and tetrabromoaurate anions. The additives initiate a rapid assembly process by co-occupying the binding cavity of ?-cyclodextrin along with the tetrabromoaurate anions, leading to the formation of supramolecular polymers that precipitate from aqueous solutions as cocrystals. The efficiency of gold recovery reaches 99.8% when dibutyl carbitol is deployed as the additive. This cocrystallization is highly selective for square-planar tetrabromoaurate anions. In a laboratory-scale gold-recovery protocol, over 94% of gold in electronic waste was recovered at gold concentrations as low as 9.3 ppm. This simple protocol constitutes a promising paradigm for the sustainable recovery of gold, featuring reduced energy consumption, low cost inputs, and the avoidance of environmental pollution.
[0036] Disclosed herein are high-efficiency gold recovery methods utilizing ?-cyclodextrin. The composition and methods described herein provide an environmentally benign, highly efficient, and thoroughly selective processes for gold recovery. As further described herein, contacting a macrocycle with gold halide anions creates adducts where the gold halide anions are reversibly bound to the outer surface of the macrocycle by non-covalent interactions, allowing of the efficient production of precipitates that may be separated from their gold bearing source material. The Examples demonstrate the trapping of metal halide ions, such as [AuBr.sub.4].sup.? anions, as their acids and alkali salts with a cyclodextrin macrocycle facilitated by the multiple weak [AuX.Math..Math..Math.HC] (X=Cl/Br) hydrogen bonding and [AuX.Math..Math..Math.CO] (X=Cl/Br) ion-dipole interactions. A gold recovery efficiency of 99.8% is achieved when dibutyl carbitol is used as the additive.
[0037] An adduct is a new chemical species AB, each molecular entity of which is formed by direct combination of two separate molecular entities A and B in such a way that there is change in connectivity, but no loss, of atoms within the moieties A and B. Stoichiometries other than 1:1 are also possible, such as 2:1, 3:1, 4:1 and so forth.
[0038] The adduct is formed from a metal halide anion non-covalently bound to the outer surface of a macrocycle. Macrocycles are a cyclic macromolecular or a macromolecular cyclic portion of a macromolecule. A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass.
[0039] The term cyclodextrin refers to any of the known cyclodextrins such as unsubstituted cyclodextrins containing from six to twelve glucose units, especially, alpha-cyclodextrin, beta-cyclodextrin, gamma-cyclodextrin and/or their derivatives and/or mixtures thereof. The alpha-cyclodextrin consists of six glucose units, the beta-cyclodextrin consists of seven glucose units, and the gamma-cyclodextrin consists of eight glucose units arranged in donut-shaped rings. The specific coupling and conformation of the glucose units give the cyclodextrins rigid, conical molecular structures with hollow interiors of specific volumes. The lining of each internal cavity is formed by hydrogen atoms and glycosidic bridging oxygen atoms; therefore, this surface is fairly hydrophobic. The unique shape and physical chemical properties of the cavity enable the cyclodextrin molecules to absorb inorganic or organic molecules or parts of inorganic or organic molecules which can fit into the cavity.
[0040] In some embodiments, the molecular receptor is cyclodextrin derivatives or modified cyclodextrins. The derivatives of cyclodextrin consist mainly of molecules wherein some of the OH groups are converted to OR groups. The cyclodextrin derivatives can, for example, have one or more additional moieties that provide additional functionality, such as desirable solubility behavior and affinity characteristics. Examples of suitable cyclodextrin derivative materials include methylated cyclodextrins (e.g., RAMEB, randomly methylated beta-cyclodextrins), hydroxyalkylated cyclodextrins (e.g., hydroxypropyl-cyclodextrin and hydroxypropyl-gamma-cyclodextrin), acetylated cyclodextrins (e.g., acetyl-gamma-cyclodextrin), reactive cyclodextrins (e.g., chlorotriazinyl-CD), branched cyclodextrins (e.g., glucosyl-beta-cyclodextrin and maltosyl-cyclodextrin), sulfobutyl-cyclodextrin, and sulfated cyclodextrins.
[0041] Cyclodextrin derivatives are also disclosed in U.S. Pat. No. 6,881,712 and include, e.g., cyclodextrin derivatives with short chain alkyl groups, such as methylated cyclodextrins and ethylated cyclodextrins, where R is a methyl or an ethyl group; those with hydroxyalkyl substituted groups, such as hydroxypropyl cyclodextrins and/or hydroxyethyl cyclodextrins, where R is a CH.sub.2CH(OH)CH.sub.3 or a CH.sub.2CH.sub.2OH group; branched cyclodextrins such as maltose-bonded cyclodextrins; cationic cyclodextrins such as those containing 2-hydroxy-3-(dimethylamino)propyl ether, where R is CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 which is cationic at low pH; quaternary ammonium, e.g., 2-hydroxy-3-(trimethylammonio)propyl ether chloride groups, where R is CH.sub.2CH(OH)CH.sub.2N.sup.+ (CH.sub.3).sub.3Cl.sup.?; anionic cyclodextrins such as carboxymethyl cyclodextrins, cyclodextrin sulfates, and cyclodextrin succinylates; amphoteric cyclodextrins such as carboxymethyl/quaternary ammonium cyclodextrins; cyclodextrins wherein at least one glucopyranose unit has a 3-6-anhydro-cyclomalto structure, e.g., the mono-3-6-anhydrocyclodextrins, as disclosed in Optimal Performances with Minimal Chemical Modification of Cyclodextrins, F. Diedaini-Pilard and B. Perly, The 7th International Cyclodextrin Symposium Abstracts, April 1994, p. 49 said references being incorporated herein by reference; and mixtures thereof. Other cyclodextrin derivatives are disclosed in U.S. Pat. No. 3,426,011, Parmerter et al., issued Feb. 4, 1969; U.S. Pat. Nos. 3,453,257; 3,453,258; 3,453,259; and 3,453,260, all in the names of Parmerter et al., and all issued Jul. 1, 1969; U.S. Pat. No. 3,459,731, Gramera et al., issued Aug. 5, 1969; U.S. Pat. No. 3,553,191, Parmerter et al., issued Jan. 5, 1971; U.S. Pat. No. 3,565,887, Parmerter et al., issued Feb. 23, 1971; U.S. Pat. No. 4,535,152, Szejtli et al., issued Aug. 13, 1985; U.S. Pat. No. 4,616,008, Hirai et al., issued Oct. 7, 1986; U.S. Pat. No. 4,678,598, Ogino et al., issued Jul. 7, 1987; U.S. Pat. No. 4,638,058, Brandt et al., issued Jan. 20, 1987; and U.S. Pat. No. 4,746,734, Tsuchiyama et al., issued May 24, 1988; all of said patents being incorporated herein by reference. In some embodiments, the molecular receptor is ?-cyclodextrin.
[0042] The metal halide anion comprises a noble metal. In some embodiments, the metal halide anion is a square-planar anion such as [MX.sub.4].sup.? where M is a noble metal, such as Au, and X is a halide. The metal halide anion may comprise other noble metals such as Pt or Pd. Each halide may be the same, such as for [AuBr.sub.4].sup.?. In other embodiments, the metal halide anion may comprise two or more different halides. In some embodiments, the metal halide anion is provided with a counter anion such as H.sup.+ or metal cation, such as an alkali cation.
[0043] Superstructures and crystalline compositions may be formed from adducts described herein. A crystalline composition is a material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice. A superstructure is a material having additional structure superimposed upon a given crystalline material, supramolecular assembly, or other well-defined substructure.
[0044] A supramolecular assembly is a well-defined complex of molecules held together by noncovalent bonds. Suitably, supramolecular assemblies may have well defined order in one, two, or three dimensions. The supramolecular assemblies described herein between the gold halide anion and the outer surface of the macrocycle may include hydrogen bonds and/or ion-dipole interactions, such as [AuX.Math..Math..Math.HC] and [AuX.Math..Math..Math.C?O], respectively.
[0045] In some embodiments, the well-defined substructure may be a supramolecular polymer. Supramolecular polymers are polymeric arrays of monomer units, held together by reversible and directional non-covalent interactions, such as hydrogen bonds. The resulting materials therefore maintain their polymeric properties in solution. The directions and strengths of the interactions are tuned so that the array of molecules behaves as a polymer. The high reversibility of the non-covalent bonds ensures that supramolecular polymers are always formed under conditions of thermodynamic equilibrium. The lengths of the chains are directly related to the strength of the non-covalent bond, the concentration of the monomer, and the temperature.
[0046] The compositions described herein may be used for the isolation and recovery of gold from gold-bearing materials. A gold-bearing material is material comprised of gold atoms, regardless of oxidation state. Exemplary gold-bearing materials include, without limitation, ores, metal mixtures, or post-consumer products.
[0047] The term metal mixture refers to two or more elements from Groups IA, IIA, IB to VIIIB, the lanthanide series and actinide series of the periodic table. An example of a metal mixture is Au and Pt.
[0048] The term post-consumer product refers to any man-made product for consumption, bartering, exchange or trade. Examples of post-consumer product include a jewelry item, an electronics item, precious metal products, and coins, among others.
[0049] The term jewelry item includes any aesthetic item that includes as one component a precious metal. Examples of a jewelry item include a ring, a bracelet and a necklace, among others.
[0050] The term electronics item refers to a product that includes at least one circuit for conducting electron flow. Examples of an electronics item include a computer, a monitor, a power supply, an amplifier, and a preamplifier, a digital to analog converter, an analog to digital converter, and a phone, among others.
[0051] The term precious metal product includes a partially purified form or a purified form of a noble metal, such as gold, platinum, palladium and silver. Examples of a precious metal include a powder, ingot, or bar of gold, silver, platinum, among others. As used herein, partially-purified form refers to a form having from about 10% to about 75% of the pure form of a noble metal. As used herein, purified form refers to a form having greater than about 75% of the pure form of a noble metal.
[0052] The term coin refers to any pressed object composed of a pure metal, mixed metal or metal alloy that can be used as a currency, a collectable, among other uses. As used herein, pure metal refers to a single metal of at least 95% or greater purity. As used herein mixed metal refers to two or more metals. As used herein metal alloy refers to a mixture or solid solution of a metal with at least one other element.
[0053] A method for isolating and recovering gold from gold-bearing materials was developed based upon the selective co-precipitation of metal halide anions non-covalently bound to the outer surface of macrocycles. Referring to
[0054] In some embodiments, not all of gold-bearing material can be dissolved in a gold halide solution. As a result, some solid remnants of gold-bearing material (whether or not including gold) can persist. In such aspects, it may be desirable to include a filtration step to remove the solid remnants prior to subsequent processing. The resultant filtrate may be processed as described above to obtain the isolated gold.
[0055] The method for isolating and recovering gold from gold-bearing materials has several applications. In one aspect, the method can be applied to isolating gold from gold-bearing material, wherein the gold-bearing material is selected from an ore, a metal mixture, or a post-consumer product. The foregoing examples of isolating gold from gold-bearing materials are not limited to the foregoing materials. The specific etching and leaching process for dissolving gold from gold-bearing materials results in formation of a specific gold-halide compound that can be recovered in the form of a complex with the macrocycle, thereby rendering the method suitable for recovering gold from each of these particular applications as well as other gold-bearing materials.
[0056] Unless otherwise specified or indicated by context, the terms a, an, and the mean one or more. For example, a molecule should be interpreted to mean one or more molecules.
[0057] As used herein, about, approximately, substantially, and significantly will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, about and approximately will mean plus or minus?10% of the particular term and substantially and significantly will mean plus or minus >10% of the particular term.
[0058] As used herein, the terms include and including have the same meaning as the terms comprise and comprising. The terms comprise and comprising should be interpreted as being open transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms consist and consisting of should be interpreted as being closed transitional terms that do not permit the inclusion additional components other than the components recited in the claims. The term consisting essentially of should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.
[0059] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
[0060] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
[0061] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
EXAMPLES
[0062] Herein, we demonstrate a de novo additive-induced gold separation paradigm based on precisely controlling the reciprocal transformation of the second-sphere coordinated adducts formed between ?-CD and [AuBr.sub.4].sup.? anions. Mechanistic investigations reveal that the additives drive rapid assembly of ?-CD and [AuBr.sub.4].sup.? anions by forcing the [AuBr.sub.4].sup.? anions to move from the inner cavity to the primary faces of two ?-CD tori, while the additives occupy the space between the secondary faces of the two ?-CD tori, thus forming one-dimensional supramolecular polymers that precipitate from aqueous solutions as cocrystals. A wide range of common organic solvents can be employed as additives. Solvents with high boiling points provide higher gold-recovery efficiencies. A gold-recovery efficiency of 99.8% has been achieved when dibutyl carbitol is used as the additive. The rapid cocrystallization is highly selective for [AuBr.sub.4].sup.? anions, while no precipitate is observed when using metal cations along with other structurally similar anions, such as [PdBr.sub.4].sup.2? and [PtBr.sub.4].sup.2?. A laboratory-scale gold-recovery protocol, aligned with an attractive strategy for the practical recovery of gold metal, has been established, wherein 94% of gold is recovered directly from a leaching solution of gold-bearing scrap at gold concentrations as low as 9.3 ppm.
Encapsulation KAuBr.SUB.4 .by ?-Cyclodextrin
[0063] Second-sphere coordination (
[0064] The solid-state superstructure of the 1:1 complex was determined unambiguously by single-crystal X-ray diffraction analysis. Brown single crystals were obtained by slowly cooling an aqueous solution of KAuBr.sub.4 and ?-CD from 90? C. to room temperature over 6 h. The [AuBr.sub.4].sup.? anion, which is encapsulated (
Additive-Induced Supramolecular Polymerization
[0065] Upon adding a trace amount of common organic solvents, which serve as additives, to a 1 M HBr aqueous solution of the KAuBr.sub.4??-CD complex, brown co-precipitates form immediately. (
[0066] Filtration of the suspension, which was obtained upon the addition of DBC to an aqueous solution of the KAuBr.sub.4??-CD complex, led to the isolation of a brown solid. The Fourier transform infrared (FTIR) spectrum of this solid reveals (
Mechanism of Additive-Induced Supramolecular Polymerization
[0067] The mechanism for the DBC-induced supramolecular polymerization has been elucidated by X-ray crystallography. Brown single crystals of the ternary complex formed between KAuBr.sub.4, ?-CD, and DBC were obtained by slow vapor diffusion of DBC into an aqueous solution of KAuBr.sub.4 and ?-CD over 3 days. Single-crystal X-ray diffraction analysis reveals that the [AuBr.sub.4].sup.? anion is centered (
[0068] Based on the solid-state superstructures of [AuBr.sub.4].sup.? and ?-CD, obtained before and after adding DBC, we propose the mechanism (
[0069] Brown cocrystals of the HAuBr.sub.4.Math.2(iPr.sub.2O)?2?-CD adduct were also obtained after layering iPr.sub.2O on top of an aqueous solution of the [AuBr.sub.4].sup.???-CD complex for 12 h. X-Ray crystallography reveals that the HAuBr.sub.4.Math.2(iPr.sub.2O)?2?-CD complex adopts (Table 5) the same triclinic space group P1 as that of the HAuBr.sub.4.Math.DBC?2?-CD complex. In its solid-state superstructure, the [AuBr.sub.4].sup.? anions are located (
[0070] The PXRD confirms the cocrystal-to-cocrystal transformation. The PXRD patterns of the co-precipitates, obtained by adding iPr.sub.2O to the mixture of ?-CD and [AuBr.sub.4].sup.? anions, change (
[0071] We believe that several factors need to be considered when choosing suitable additives to recover gold based on our results. They include-(i) Additives should be hydrophobic and possess a relatively high binding affinity for ?-CD, which allows them to participate in the co-assembly process. (ii) Additives should be size-matched with the cavity of ?-CD and able to share the cavity together with the [AuBr.sub.4].sup.? anion, which allows for the formation of ID supramolecular nanostructures. (iii) Additives with high boiling points are preferred when it comes to improving the stability of the cocrystals. (iv) Additives should be cheap and readily available, so as to reduce costs. (v) Additives should be eco-friendly, an attribute which is vital to sustainable development and environmental protection.
Gold Recovery from Gold-Bearing Scrap
[0072] In order to develop a feasible gold-recovery protocol based on additive-induced supramolecular polymerization, the influence of CD and gold salts on gold-recovery efficiency was also investigated. The ?-CD-to-KAuBr.sub.4 ratio was optimized first of all. Six samples with different molar ratios of ?-CD-to-KAuBr.sub.4 from 0.5 to 3 were prepared. After adding 0.1% (v/v) of DBC, all six clear solutions turned cloudy. The UV-Vis absorption spectra reveal (
[0073] The effect of the countercation of the gold salts on gold-recovery efficiency has also been investigated. After adding 0.1% (v/v) of DBC to the two aqueous solutions containing NaAuBr.sub.4??-CD and HAuBr.sub.4CB-CD complexes, a large amount of brown co-precipitates was formed in both solutions. The corresponding gold-recovery efficiencies (
[0074] The high performance of additive-induced cocrystallization between ?-CD and [AuBr.sub.4].sup.? motivated us to test the practicability of recovering gold from electronic scrap. A spent gold-bearing alloy cable was employed as a sample for developing a laboratory-scale gold-recovery protocol. The cable was etched (
[0075] In the X-ray photoelectron spectrum of the microcrystals, only the characteristic peaks of carbon, oxygen, bromine and gold were observed (
DISCUSSION
[0076] An eco-friendly and sustainable supramolecular metallurgical technology for gold recovery has been demonstrated. It is based on an additive-induced supramolecular polymerization of second-sphere coordinated adducts formed between ?-cyclodextrin and tetrabromoaurate anions. The additives drive the assembly by obliging the tetrabromoaurate anions to move from the inner cavity to the primary face of two ?-cyclodextrin tori, while themselves occupying the space between the secondary faces of two ?-cyclodextrin tori, leading to the formation of infinite 1D supramolecular nanostructures that precipitate from the aqueous solutions as cocrystals. This additive-induced supramolecular polymerization, not only provides a feasible method for the rapid crystallization of the supramolecular polymers, but it also opens the door for regulating the assembly behavior of second-sphere coordinated adducts.
[0077] In contrast to the traditional antisolvent precipitation method, the additive-induced polymerization reported in this research provides the following advantages-(i) It only requires a small volume fraction (<0.3%) of additives to effectively precipitate the target compound with a high recovery efficiency (>99.5%). (ii) The additives do not have to be mixable with the solution. (iii) The molecular recognition driven supramolecular polymerization is highly selective for the precipitation of target compounds in the presence of other structurally similar substrates.
[0078] From a practical viewpoint, this research describes a highly efficient and sustainable gold-recovery protocol. Compared with our previously reported.sup.54 protocol using ?-cyclodextrin, the additive-induced polymerization with ?-cyclodextrin comes with the following attributes (i) The gold-recovery can be performed at a low concentration (9.3 ppm) with a much better recovery efficiency (>94%). (ii) No additional potassium ions are needed. (iii) Co-precipitation can be performed directly in acidic leaching solutions without the need of neutralization. (iv) The cost of ?-cyclodextrin is lower than that of ?-cyclodextrin. In summary, our establishment of additive-induced polymerization constitutes an attractive strategy for the practical recovery of gold and leads to significantly reduced energy consumption, cost inputs, and environmental pollution. We are currently optimizing the strategy to recover gold from lower-concentration gold-bearing e-waste and exploring the generality of this strategy to separate other target metal ions.
Methods
[0079] Materials. The compounds HAuBr.sub.4, NaAuBr.sub.4, KAuBr.sub.4, K.sub.2PdBr.sub.4, K.sub.2PtBr.sub.4, ?-CD, ?-CD, DBr (wt 47-49%) in D.sub.2O, HBr (wt 47-49%) and H.sub.2O.sub.2 (wt 30%) were purchased from commercial suppliers and used without further purification. All the additives, i.e., dibutyl carbitol (DBC), isopropyl ether (iPr.sub.2O), diethyl ether (Et.sub.2O), hexane, ethyl acetate, dichloromethane (CH.sub.2Cl.sub.2), chloroform (CHCl.sub.3), benzene, toluene, olive oil, vegetable oil and pump oil are commercially available. Ultra pure water was generated by a Milli-Q system.
[0080] UV-Vis Absorption spectroscopy. UV-Vis Absorption spectra were recorded in 1 M HBr aqueous solutions at 298 K. UV-Vis Absorption spectra were recorded on a UV-3600 Shimadzu spectrophotometer in rectangular quartz cells with light paths of 4 mm. Each gold-recovery experiment was duplicated independently, and the average gold-recovery efficiencies are presented with their standard deviations.
[0081] Fourier-transform infrared spectroscopy. Fourier-transform infrared (FT-IR) spectroscopy was performed on a Nexus 870 spectrometer (Thermo Nicolet) in the mode of attenuated total reflection (ATR) with the range from 4000 to 600 cm.sup.?1 and at a resolution of 0.125 cm.sup.?1.
[0082] NMR Spectroscopy. NMR Spectra were recorded on a Bruker Avance III 600 MHZ spectrometer in D.sub.2O containing 0.5 M DBr. Chemicals shifts (8) are given in ppm with residual H.sub.2O signals as a reference. .sup.1H NMR Titrations: Highly-concentrated solutions of KAuBr.sub.4, K.sub.2PdBr.sub.4, or K.sub.2PtBr.sub.4 in D.sub.2O (containing 0.5 M DBr) as the titrating solution was added dropwise to a D.sub.2O solution (containing 0.5 M DBr) of ?-CD or ?-CD. Binding constants were obtained by fitting a 1:1 isotherm according to the programs available at http://app.supramolecular.org/bindfit/. Crystallization and single-crystal X-ray diffraction analyses. The KAuBr.sub.4??-CD complex: Brown single crystals were obtained by slowly cooling an aqueous solution of KAuBr.sub.4 and ?-CD from 90? C. to room temperature over 6 h. The HAuBr.sub.4DBC?2?-CD complex: Brown single crystals were obtained by slow vapor diffusion of DBC into an aqueous solution of KAuBr.sub.4 containing 2 molar equivalents of ?-CD over 3 days. The HAuBr.sub.4.Math.2(iPr.sub.2O)?2?-CD complex (Cocrystal A): Brown single crystals were obtained by slow liquid-liquid diffusion of iPr.sub.2O into an aqueous solution containing KAuBr.sub.4 and 2 molar equivalents of ?-CD over 12 h. The 0.5(HAuBr.sub.4)=2?-CD complex (Cocrystal B): Brown single crystals were obtained by allowing the HAuBr.sub.4.Math.2(iPr.sub.2O)=2?-CD suspension to stand at room temperature for 3 days. The suitable crystals were mounted on a MITIGEN holder in Paratone oil on a Rigaku XtaLAB Synergy, Single source at home/near, HyPix diffractometer using CuK? (?=1.5418 ?) or MoK? (?=0.7107 ?) radiation. Data were collected using the Bruker APEX-II or Rigaku CrysAlis Pro program. The superstructures were solved with the ShelXT program using intrinsic phasing and refined with the ShelXL refinement package using least squares minimization in OLEX2 software.
[0083] Powder X-ray diffraction analysis. Powder X-ray diffraction (PXRD) analyses were performed on an STOE-STADI MP powder diffractometer equipped with an asymmetrically curved Germanium monochromator (Cu-K?1 radiation, ?=1.54056 ?) and a one-dimension silicon strip detector (MYTHEN2 1K from DECTRIS). Samples for superstructural analysis were measured at room temperature in transmission mode. The simulated PXRD patterns were calculated using the Mercury software 4.3.0.
[0084] X-Ray photoelectron spectroscopy. X-Ray photoelectron spectroscopic (XPS) analyses were conducted on a fully digital state-of-the-art X-ray photoelectron spectrometer (Thermo Scientific ESCALAB 250Xi), which was equipped with an electron flood gun and a scanning ion gun. The diameter of the X-ray spot was 500 ?m, and the scan range was from 0 to 1200 eV.
[0085] Inductively coupled plasma mass spectrometry. ICP-MS was performed on a computer-controlled (QTEGRA software) Thermo iCapQ ICP-MS (Thermo Fisher Scientific, Waltham, MA, USA) operating in STD mode and equipped with an ESI SC-2DX PrepFAST autosampler (Omaha, NE, USA). The internal standard was added inline using the prepFAST system and consisted of 1 ng/ml of a mixed element solution containing Bi, In, .sup.6Li, Sc, Tb, Y (IV-ICPMS-71D from Inorganic Ventures). Online dilution was also carried out by the prepFAST system and used to generate a calibration curve consisting of 100, 50, 20, 10, 5 and 1 ppb Au. Each sample was acquired using one survey run (10 sweeps) and three main (peak jumping) runs (40 sweeps). The isotopes selected for analysis were .sup.197Au and .sup.89Y, .sup.115In, .sup.159Tb, and .sup.209Bi (chosen as internal standards for data interpolation and machine stability). Instrument performance was optimized daily by auto-tuning, followed by verification with the aid of a performance report.
[0086] Scanning electron microscopy. Scanning electron microscopic (SEM) images were obtained on a SU8030 scanning electron microscope at the voltages of 10/15 kV, while the energy-dispersive X-ray spectroscopy (EDS) elemental maps were recorded at 15 kV.
[0087] Density functional theory calculations. The superstructures from the single-crystal X-ray diffraction were used for the density functional theory (DFT) calculations in the Orca program (version 4.1.2) using the hybrid generalized gradient approximation (GGA) Becke three-parameter Lec-Yang-Parr (B3LYP) functional, the Ahlrich's double zeta basis set with a polarization function Def2-SVP, and Grimme's third generation atom-pairwise dispersion correction with Becke Johnson damping (D.sub.3BJ); an integration grid of four was used throughout. To further speed up the DFT optimizations, the Coulomb integral and numerical chain-of-sphere integration for the HF exchange (RIJCOSX) method was applied with the Def2/J auxiliary basis.
[0088] Additive-induced ternary cocrystallization experiments. Aqueous stock solutions of KAuBr.sub.4 were prepared by dissolving directly the corresponding commercially available salt in an aqueous HBr (2 M) solution, while an aqueous solution of ?-CD was prepared by dissolving the ?-CD powder in ultra purity water. The addition of 2 molar equivalents of ?-CD (1 mL, 10 mM) to a KAuBr.sub.4 (1 mL, 5 mM) aqueous solution led to the formation of a 1:1 KAuBr.sub.4??-CD complex. When specific additives (0.1% v/v) were added to the resulting aqueous solutions, yellow suspensions were formed immediately. The yellow solids were isolated by filtration, washed, and air-dried. The concentrations of [AuBr.sub.4].sup.? remaining in the filtrates were determined by UV-Vis absorption spectroscopy or ICP-MS analysis. The metal precipitation yields were calculated based on the aqueous solution's initial and residual concentrations of metal anions.
[0089] Gold recovery from scrap. A gold-bearing cable was obtained from the local electronic junk shop. The yellow cable (15 mg) was firstly leached with a mixture of HBr and H.sub.2O.sub.2 overnight. Subsequently, the acid concentration in the HAuBr.sub.4-containing leaching solution was adjusted to 1 M with ultra pure H.sub.2O, and the insoluble impurities were removed by filtration. A saturated aqueous solution of ?-CD containing ?1 M HBr was added to the leaching solution, forming the HAuBr.sub.4CB-CD complex. Upon adding 0.1% (v/v) of DBC, the solution became gradually cloudy. After stirring for 5 mins, the co-precipitate of HAuBr.sub.4.Math.DBC?2?-CD was separated from other metals by filtration and washed with ultra pure H.sub.2O. The metals trapped in the co-precipitates were analyzed by ICP-MS by comparing with the metal concentrations of the solution before and after adding DBC. In order to convert the [AuBr.sub.4].sup.? anions tapped in the co-precipitate to gold metal, the HAuBr.sub.4.Math.DBC?2?-CD co-precipitates were dispersed in an aqueous solution and reduced with N.sub.2H.sub.4.Math.H.sub.2O. After centrifugation and washing with H.sub.2O to dissolve the residual ?-CD, gold metal was obtained. ?-CD, which dissolves in the aqueous solution, can be recycled by precipitating with acetone and followed by recrystallization.
(1) Crystal Superstructure of KAuBr.SUB.4.??-CD
[0090] (a) Method. Brown block-like crystals were obtained by slow cooling of an aqueous solution of KAuBr.sub.4 (100 mM) and ?-CD (100 mM) from 90? C. down to room temperature over 6 h. A suitable crystal was selected and mounted on a MITIGEN holder with Paratone oil on an XtaLAB Synergy, Single source at home/near, HyPix diffractometer. The crystals were kept at 100.07 K during the data collection. Using Olex2,.sup.57 the structure was solved with the ShelXT.sup.58 structure solution program using Intrinsic Phasing and refined with the XL.sup.59 refinement package employing Least Squares Minimization. Crystallographic images were produced using Mercury 4.3.0. Distances were measured employing Mercury 4.3.0. The solid-state superstructure of KAuBr.sub.4??-CD is shown in
TABLE-US-00001 TABLE 1 Intermolecular short distances.sup.a (?) between [AuBr.sub.4].sup.? and the inner protons H-5 and H-6 in each of the seven glucose subunits of ?-CD Distances.sup.a/? Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Br1/Br2-H6 3.8-4.2 3.4-4.1 3.2-4.9 4.1-4.2 3.6-3.7 3.5-4.4 3.4 Br1/Br2-H5 3.7 4.6-4.8 3.6 3.3-3.5 3.5 3.6-4.7 3.1 Br3/Br4-H6 4.8 4.4-4.9 4.7 N.sup.b 4.5 4.8-4.9 4.6 Br3/Br4-H5 3.6 4.4-4.5 3.3 3.3 3.4 3.3-4.7 3.0 .sup.aShort distance means the distance between two atoms <5 ?. .sup.bN means no interaction between two atoms.
(2) Crystal Superstructure of HAuBr.SUB.4..Math.DBC?2?-CD
[0093] (a) Method. Two molar equivalents of ?-CD (500 ?L, 20 mM) were added to an aqueous KAuBr.sub.4 (500 ?L, 10 mM) solution containing 1 M HBr. The resulting solution was added to two 1 mL tubes with volumes of 0.20 and 0.45 mL. The tubes were placed in one 20 mL vial containing DBC (100 ?L). The vial was sealed with a cap. Slow vapor diffusion of DBC into the mixture of KAuBr.sub.4 and ?-CD over the period of 3 days yielded brown single crystals. A suitable crystal was selected and mounted on a MITIGEN holder with Paratone oil on an XtaLAB Synergy, Single source at home/near, HyPix diffractometer. The crystal was kept at 100.15 K during the data collection. Using Olex2,.sup.57 the structure was solved with the ShelXT.sup.58 structure solution program using Intrinsic Phasing and refined with the XL.sup.59 refinement package employing Least Squares Minimization. Crystallographic images were produced using Mercury 4.3.0. Distances were measured employing Mercury 4.3.0. The solid-state superstructure of HAuBr.sub.4.Math.DBC?2?-CD is shown in
TABLE-US-00002 TABLE 2 Intermolecular short distances.sup.a (?) between [AuBr.sub.4].sup.? and the inner protons H-5 and H-6 in each of the seven glucose subunits of the two ?-CD tori (A and B) Distances.sup.a/? Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Br1/Br2-[A]H6 N.sup.b N.sup.b 3.4-3.7 3.3-3.8 4.5 3.2-3.4 3.5-4.3 Br1/Br2-[A]H5 N.sup.b 4.9 3.4 3.2 4.7-4.9 3.5 3.5 Br1/Br2-[B]H6 N.sup.b N.sup.b N.sup.b 3.0-3.8 3.3-4.2 3.0-3.2 4.8 Br3/Br4-[B]H6 4.2-4.4 3.3-4.9 3.2-3.3 4.4-4.8 N.sup.b 4.3-4.6 3.3-3.5 Br3/Br4-[B]H5 4.1 3.5-4.8 3.2 4.4 4.9 3.7 3.4 Br3/Br4-[A]H6 3.3-4.7 3.3-3.5 4.1 N.sup.b N.sup.b N.sup.b 3.5-3.6 .sup.aShort distance means the distance between two atoms <5 ?. .sup.bN means no interaction between two atoms.
(3) Crystal Superstructure of HAuBr.sub.4.Math.2(iPr.sub.2O)?2?-CD (Cocrystal A) [0096] (a) Method. Two molar equivalents of ?-CD (500 ?L, 20 mM) were added to an aqueous KAuBr.sub.4 (500 ?L, 10 mM) solution containing 1 M HBr. iPr.sub.2O (20 ?L) was layered on top of the mixture of KAuBr.sub.4 and ?-CD. High-quality brown crystals were obtained after liquid-liquid diffusion for 12 h. A suitable crystal was selected and mounted on a MITIGEN holder with Paratone oil on an XtaLAB Synergy, Single source at offset/far, HyPix diffractometer. The crystal was kept at 99.9 K during the data collection. Using Olex2,.sup.57 the structure was solved with the ShelXT.sup.58 structure solution program using Intrinsic Phasing and refined with the XL.sup.59 refinement package employing Least Squares Minimization. Crystallographic images were produced using Mercury 4.3.0. Distances were measured employing Mercury 4.3.0. The solid-state superstructure of HAuBr.sub.4.Math.2(iPr.sub.2O)?2?-CD is shown in
TABLE-US-00003 TABLE 3 Intermolecular short distances.sup.a (?) between [AuBr.sub.4].sup.? and the inner protons H-5 and H-6 in each of the seven glucose subunits of the two ?-CD tori (A and B) Distances.sup.a/? Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Br1/Br2-[A]H6 N.sup.b 4.3-4.8 3.3-4.0 3.4-4.8 4.5-4.6 3.2-3.4 4.0-4.4 Br1/Br2-[A]H5 N.sup.b 4.4 3.3 3.6 4.4 3.7 3.6 Br1/Br2-[B]H6 N.sup.b N.sup.b 4.2 3.2-3.4 3.1-4.5 3.2-3.3 N.sup.b Br3/Br4-[B]H6 4.2-4.9 3.3-3.7 3.3-3.7 4.9 N.sup.b 3.7-4.3 3.3-3.5 Br3/Br4-[B]H5 4.5-4.8 3.2 3.4 4.8 4.9 3.5 3.2 Br3/Br4-[A]H6 3.3-4.3 2.9-3.7 4.8 N.sup.b N.sup.b N.sup.b 3.1-3.3 .sup.aShort distance means the distance between two atoms <5 ?. .sup.bN means no interaction between two atoms.
(4) Crystal Superstructure of 0.5(HAuBr.SUB.4.)?2?-CD (Cocrystal B)
[0099] (a) Method. Two molar equivalents of ?-CD (500 ?L, 20 mM) were added to an aqueous KAuBr.sub.4 (500 ?L, 10 mM) solution containing 1 M HBr in a 3 mL vial without the cap. iPr.sub.2O (20 ?L) was layered carefully on top of the mixture of KAuBr.sub.4 and ?-CD. High-quality brown crystals were obtained after liquid-liquid diffusion for 3 days. A suitable crystal was selected and mounted on a MITIGEN holder with Paratone oil on an XtaLAB Synergy, Single source at offset/far, HyPix diffractometer. The crystal was kept at 100.0 K during the data collection. Using Olex2,.sup.57 the structure was solved with the ShelXT.sup.58 structure solution program using Intrinsic Phasing and refined with the XL.sup.59 refinement package employing Least Squares Minimization. Crystallographic images were produced using Mercury 4.3.0. Distances were measured employing Mercury 4.3.0. The solid-state superstructure of 0.5(HAuBr.sub.4)?2?-CD is shown in
TABLE-US-00004 TABLE 4 Intermolecular short distances.sup.a (?) between [AuBr.sub.4].sup.? and the inner protons H-5 and H-6 in each of the seven glucose subunits of the two B-CD tori (A and B) Distances.sup.a/? Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Br1/Br2-[A]H6 N.sup.b 4.9 3.1-3.6 3.0-3.4 3.4-4.5 3.5 3.4-3.8 Br1/Br2-[A]H5 4.8 4.9 3.2 2.9 4.1-4.4 3.1 3.2 Br1/Br2-[B]H6 N.sup.b N.sup.b N.sup.b 3.4-4.2 3.2-4.5 3.2-3.3 N.sup.b Br3/Br4-[B]H6 4.7 4.6 3.4-3.8 4.1-4.4 4.6-4.7 3.5-4.0 2.8-3.1 Br3/Br4-[B]H5 N.sup.b 4.6 3.9 4.2 4.5 3.4 3.6 Br3/Br4-[A]H6 3.1-4.4 3.4-3.6 3.9-4.7 N.sup.b N.sup.b N.sup.b 3.2-3.4 .sup.aShort distance means the distance between two atoms <5 ?. .sup.bN means no interaction between two atoms.
TABLE-US-00005 TABLE 5 Crystallographic data for the complexes formed between ?-CD and [AuBr.sub.4].sup.? before and after adding additives Complex KAuBr.sub.4??-CD KAuBr.sub.4DBC?2?-CD KAuBr.sub.42(iPr.sub.2O)?2?-CD Empirical formula C.sub.42H.sub.70O.sub.35KAuBr.sub.44(H.sub.2O) 2(C.sub.42H.sub.70O.sub.35)HAuBr.sub.4C.sub.12H.sub.26O.sub.314(H.sub.2O) 2(C.sub.42H.sub.70O.sub.35)HAuBr.sub.42(C.sub.6H.sub.14O)8(H.sub.2O) Formula weight 1762.75 3258.11 3136.04 T/K 100.07(16) 100.15 99.9(3) Crystal system monoclinic triclinic triclinic Space group P2.sub.1 P1 P1 a/? 14.90540(10) 15.11370(18) 15.1182(8) b/? 15.43740(10) 15.50618(18) 15.3034(9) c/? 14.91910(10) 15.7047(2) 15.5384(8) ?/? 90 88.8635(10) 87.704(4) ?/? 119.3100(10) 81.9417(10) 81.920(4) ?/? 90 77.0250(10) 76.368(5) V/?.sup.3 2993.43(4) 3550.84(8) 3458.9(3) Z 2 1 1 ?.sub.calcd/g cm.sup.?3 1.956 1.524 1.506 ?/mm.sup.?1 9.299 4.205 2.322 F (000) 1760 1686.0 1620.0 goodness- 1.067 1.068 1.017 of-fit on F.sup.2 R.sub.l [I > 2? (I)] 0.0270 0.0818 0.1437 wR.sub.2 [all data] 0.0711 0.2238 0.3894 CCDC No. 2206843 2206844 2206845 Complex 0.5(HAuBr.sub.4)?2?-CD Empirical formula 2(C.sub.42H.sub.70O.sub.35)0.5(HAuBr.sub.4)23(H.sub.2O) Formula weight 2943.12 T/K 100.0(3) Crystal system monoclinic Space group P2.sub.1 a/? 15.7110(7) b/? 24.3931(7) c/? 18.9812(7) ?/? 90 ?/? 108.544(4) ?/? 90 V/?.sup.3 6896.7(5) Z 2 ?.sub.calcd/g cm.sup.?3 1.417 ?/mm.sup.?1 1.228 F (000) 3088.0 goodness- 1.208 of-fit on F.sup.2 R.sub.l [I > 2? (I)] 0.1150 wR.sub.2 [all data] 0.3237 CCDC No. 2206846
.SUP.1.H NMR Titration
[0102] .sup.1H NMR Titrations were performed in D.sub.2O containing 0.5 M DBr at 25? C. Aliquots from a stock solution containing the appropriate amount of KAuBr.sub.4, K.sub.2PdBr.sub.4, or K.sub.2PtBr.sub.4 were added sequentially to an NMR tube containing the ?-CD or ?-CD, and a .sup.1H NMR spectrum was acquired after each addition. The titration isotherms were fitted to a 1:1 receptor-substrate binding model using Thordarson's equations..sup.61
UV-Vis Absorption Spectroscopy
[0103] The concentrations of [AuBr.sub.4].sup.? in aqueous solutions were determined by UV-Vis absorption spectroscopy employing the absorbance of [AuBr.sub.4].sup.? at ?=381 or 253 nm. The intensity of the UV-Vis absorption band at ?=381 nm correlates linearly with the concentration of [AuBr.sub.4].sup.? over the range from 50 to 150 ?M in H.sub.2O with R.sup.2=0.999. The intensity of the UV-Vis absorption band at ?=253 nm correlates linearly with the concentration of [AuBr.sub.4].sup.? over the range from 2 to 10 ?M in H.sub.2O with R.sup.2=0.999.
ICP-MS Analysis
[0104] Quantification of gold (Au) was accomplished using ICP-MS on acidified samples. Specifically, samples (100 ?L) designated for Au analysis were digested in 10 mL 2.0% HNO.sub.3 and 2.0% HCl (v/v) aqueous solution. A quantitative standard was made using a 100 ?g/mL Au elemental standard (Inorganic Ventures, Christiansburg, VA, USA), which was used to create a 100 ng/g Au standard in 2.0% HNO.sub.3 and 2.0% HCl (v/v) in a total sample volume of 50 mL. A solution of 2.0% HNO.sub.3 and 2.0% HCl (v/v) was used as the calibration blank. All the gold-recovery experiments were independently duplicated. Tables 6 and 7 show one set of data. The average gold-recovery efficiencies with standard deviations are presented in
TABLE-US-00006 TABLE 6 Effect of changes in concentration of [AuBr.sub.4].sup.? on the efficiency of recovering gold from mixture solution Concentration of Avg. Au/ Au in Filtrate/ Total Au/ Au-Recovery [AuBr.sub.4].sup.?/mM ppb ?g ?g Efficiency 0.005 34.901 0.873 0.928 0.060 0.01 36.380 0.910 1.856 0.510 0.025 22.983 0.575 4.640 0.876 0.05 24.123 0.603 9.280 0.935 0.075 30.130 0.753 13.920 0.946 0.1 42.046 1.051 18.559 0.943 0.25 43.627 1.091 46.399 0.976 0.5 23.450 0.586 92.797 0.994 0.75 36.907 0.923 139.196 0.993 1 48.028 1.201 185.594 0.994
TABLE-US-00007 TABLE 7 Changes in the efficiency of recovering gold from mixture solution with respect to adding different additives in real time Different Avg. Au/ Au in Filtrate/ Total Au/ Au-Recovery Additives ppb ?g ?g Efficiency Hexane 398.941 7.979 774.014 0.990 Benzene 130.093 2.602 774.014 0.997 Chloroform 117.617 2.352 774.014 0.997 Dichloromethane 509.513 10.190 774.014 0.987 Toluene 22.016 0.440 774.014 0.999 Isopropyl Ether 188.471 3.769 774.014 0.995 Dibutyl Carbitol 59.700 1.194 774.014 0.998
Theoretical Calculations
(1) Visualization of Noncovalent Interaction
[0105] Independent gradient model (IGM) analysis is an approach.sup.62 based on promolecular density an electron density model prior to molecule formationto identify and isolate intermolecular interactions. Strong polar attractions and Van der Waals contacts are visualized as an iso-surface. Single-crystal superstructures were used as input files. The binding surface was calculated using the Multiwfn 3.6 program.sup.63 through function 20 (visual study of weak interaction) and visualized by Chimera software.sup.64.
(2) Binding Energy
[0106] The superstructures from the single-crystal X-ray diffraction were used for the density functional theory (DFT) calculations in the Orca program.sup.65 (version 4.1.2) using the hybrid generalized gradient approximation (GGA) Becke three-parameter Lee-Yang-Parr.sup.66 (B3LYP) functional, the Ahlrich's double zeta basis set with a polarization function.sup.67 Def2-SVP, and Grimme's third generation atom-pairwise dispersion correction with Becke Johnson damping.sup.68 (D3BJ); an integration grid of four was used throughout. To further speed up the DFT optimizations, the Coulomb integral and numerical chain-of-sphere integration for the HF exchange.sup.69,70 (RIJCOSX) method was applied with the Def2/J auxiliary basis.sup.71. All calculations were single points and ran in vacuum. The binding energies were computed as ?E.sub.b=products?reactants, where products are the complexes and the reactants are the individual molecules and ions.
TABLE-US-00008 TABLE 8 Results of DFT calculation for the binding energies in HAuBr.sub.4DBC?2?-CD cocrystal Binding Electronic Energy Energy ?E.sub.b/kcal Entry E.sub.DFT/Hartree mol.sup.?1 [AuBr.sub.4].sup.? . . . [?-CD]-2 ?14700.19637 ?32.44 [AuBr.sub.4].sup.? . . . [?-CD]-3 ?14700.20786 ?39.64 [?-CD]-2 . . . [AuBr.sub.4].sup.? . . . [?-CD]-3 ?18969.56797 ?93.03 [AuBr.sub.4].sup.? . . . DBC-1 ?11128.27065 ?8.32 [AuBr.sub.4].sup.? . . . DBC-2 ?11128.27038 ?8.15 DBC-1 . . . [AuBr.sub.4].sup.? . . . DBC-2 ?11825.67981 ?16.10 DBC-1 . . . [?-CD]-1 ?4966.737547 ?35.61 DBC-1 . . . [?-CD]-2 ?4966.720184 ?30.37 [?-CD]-1 . . . DBC-1 . . . [?-CD]-2 ?9236.132379 ?110.79 [?-CD]-2 . . . [?-CD]-3 (Primary faces) ?8538.596235 ?23.32 [?-CD]-1 . . . [?-CD]-2 (Secondary faces) ?8538.634395 ?47.27 [AuBr.sub.4].sup.? . . . [?-CD]-1 . . . DBC-1 ?15397.60983 ?42.92 [AuBr.sub.4].sup.? . . . [?-CD]-2 . . . DBC-1 ?15397.65162 ?74.80 [AuBr.sub.4].sup.? . . . [?-CD]-2 . . . [?-CD]-3 . . . ?19667.0234 ?129.85 DBC-1 [AuBr.sub.4].sup.? . . . [?-CD]-2 . . . [?-CD]-3 . . . ?20364.48552 ?170.87 DBC-1 . . . DBC-2
TABLE-US-00009 TABLE 9 Results of DFT calculation for the binding energies in HAuBr.sub.42(iPr.sub.2O)?2?-CD cocrystal Binding Electronic Energy Energy ?E.sub.b/kcal Entry E.sub.DFT/Hartree mol.sup.?1 [AuBr.sub.4].sup.? . . . [?-CD]-1 ?14700.15893 ?32.47 [AuBr.sub.4].sup.? . . . [?-CD]-2 ?14700.24900 ?32.74 [?-CD]-1 . . . [AuBr.sub.4].sup.? . . . [?-CD]-2 ?18969.58363 ?84.15 [AuBr.sub.4].sup.? . . . iPr.sub.2O-1 ?10742.54258 ?3.96 [AuBr.sub.4].sup.? . . . iPr.sub.2O-2 ?10742.52625 ?7.18 iPr.sub.2O-1 . . . [AuBr.sub.4].sup.? . . . iPr.sub.2O-2 ?11054.21382 ?10.82 iPr.sub.2O-1 . . . [?-CD]-1 ?4580.967062 ?20.45 [?-CD]-1 . . . [?-CD]-2 (Primary faces) ?8538.63553 ?25.42 [?-CD]-2 . . . [?-CD]-3 (Secondary faces) ?8538.656367 ?38.49 [AuBr.sub.4].sup.? . . . [?-CD]-1 . . . iPr.sub.2O-1 ?15011.87652 ?54.94
TABLE-US-00010 TABLE 10 Results of DFT calculation for the binding energies in 0.5HAuBr.sub.4?2?-CD cocrystal Binding Electronic Energy Energy ?E.sub.b/kcal Entry E.sub.DFT/Hartree mol.sup.?1 [AuBr.sub.4].sup.? . . . [?-CD]-1 ?14700.16752 ?35.97 [AuBr.sub.4].sup.? . . . [?-CD]-2 ?14700.16005 ?29.21 [?-CD]-1 . . . [AuBr.sub.4].sup.? . . . [?-CD]-2 ?18969.54003 ?82.46 [?-CD]-1 . . . [?-CD]-2 (Primary faces) ?8538.630479 ?23.17 [?-CD]-2 . . . [?-CD]-3 (Secondary faces) ?8538.638149 ?27.98
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