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Cluster compounds containing [Mn3SrO4] and [Mn4SrO4] core structures, preparation method and application thereof

20200290031 ยท 2020-09-17

    Inventors

    Cpc classification

    International classification

    Abstract

    [Mn.sub.3SrO.sub.4] cluster compounds are synthesized in a single step from raw materials consisting of simple and inexpensive Mn.sup.2+, Sr.sup.2+ inorganic compounds and carboxylic acids by using permanganate anion as oxidant. This step can be followed by the synthesis of asymmetric biomimetic water splitting catalyst [Mn.sub.4SrO.sub.4] cluster compounds in the presence of water. The [Mn.sub.4SrO.sub.4] cluster compound can catalyze the splitting of water in the presence of an oxidant to release oxygen gas. The neutral [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2)6(R.sub.1CO.sub.2H).sub.3 cluster compound can serve as precursors for the synthesis of biomimetic water splitting catalysts, and can be utilized in the synthesis of different types of biomimetic water splitting catalysts. [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4) cluster compounds can serve as artificial water splitting catalysts, can be utilized on the surface of an electrode or in the catalyzed splitting of water driven by an anoxidant.

    Claims

    1. A [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2).sub.6(R.sub.1CO.sub.2H).sub.3 compound represented by Formula I, characterized in that the compound comprises three Mn ions and one Sr.sup.2 ion linked via four O.sup.2 ions to form a [Mn.sub.3SrO.sub.4] heteronuclear metal cluster skeleton core; the [Mn.sub.3SrO.sub.4] cluster compound has six carboxylate anions (R.sub.1CO.sub.2.sup.) and three neutral carboxylic acid ligands (R.sub.1CO.sub.2H) as the peripheral ligands; the three Mn ions all have a valence state of +4, and the whole cluster compound is electrically neutral; ##STR00015## wherein, R.sub.1 is selected from the group consisting of H and C.sub.1-8 linear or branched alkyl. Preferably, the carboxylate anion (R.sub.1CO.sub.2.sup.) may be the anion of a carboxylic acid such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid and hexanoic acid. Preferably, R.sub.1 may be hydrogen (H), methyl (CH.sub.3), ethyl (C.sub.2H.sub.5), n-propyl (CH.sub.2CH.sub.2CH.sub.3), isopropyl (CH(CH.sub.3).sub.2), n-butyl ((CH.sub.2).sub.3CH.sub.3), isobutyl (CH(CH.sub.3)C.sub.2H.sub.5), tert-butyl (C(CH.sub.3).sub.3), n-pentyl ((CH.sub.2).sub.4CH.sub.3), isopentyl (CH.sub.2CH.sub.2CH(CH.sub.3).sub.2), and the like. Preferably, the compound of Formula I is selected from the group consisting of: compound 1, [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2).sub.6(R.sub.1CO.sub.2H).sub.3, wherein R.sub.1=tert-butyl. Compound 1 is a single crystal of trigonal system with space group of R-3c, cell parameters of a=10.6575(15) , b=10.6575(15) , c=87.917(18) , =90.00, =90.00, and =120.00, Z=6, and volume of 8648(3) .sup.3. Compound 1 has the structure as shown in the following Formula I-1: ##STR00016## wherein R.sup.1 is tert-butyl;

    2. A [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4) compound represented by Formula II, characterized in that the compound comprises four Mn ions and one Sr.sup.2+ ion via four O.sup.2 ions to form an asymmetric [Mn.sub.4SrO.sub.4] heteronuclear metal cluster skeleton core; the [Mn.sub.4SrO.sub.4] cluster compound has eight carboxylate anions (R.sub.1CO.sub.2.sup.) and four neutral ligands (L.sub.1, L.sub.2, L.sub.3, L.sub.4) as the peripheral ligands; the four Mn ions have valence states of +3, +3, +4 and +4, respectively, and the whole cluster compounds is electrically neutral; ##STR00017## wherein, R.sub.1 is selected from the group consisting of H and C.sub.1-8 linear or branched alkyl; the four ligands L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are the same or different and are each independently selected from the group consisting of carboxylic acid molecules and derivatives thereof, pyridine, imidazole, pyrazine, quinoline, isoquinoline, bipyridine and derivatives thereof, or water molecule, alcohol molecules, ketones, nitriles (such as acetonitrile), esters and other exchangeable neutral small molecules. Preferably, the carboxylate anion (R.sub.1CO.sub.2.sup.) may be the anion of a carboxylic acid such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid and hexanoic acid. Preferably, R.sub.1 may be hydrogen (H), methyl (CH.sub.3), ethyl (C.sub.2H.sub.5), n-propyl (CH.sub.2CH.sub.2CH.sub.3), isopropyl (CH(CH.sub.3).sub.2), n-butyl ((CH.sub.2).sub.3CH.sub.3), isobutyl (CH(CH.sub.3)C.sub.2H.sub.5), tert-butyl (C(CH.sub.3).sub.3), n-pentyl ((CH.sub.2).sub.4CH.sub.3), isopentyl (CH.sub.2CH.sub.2CH(CH.sub.3).sub.2), and the like. Preferably, the compound of Formula II is selected from the group consisting of: [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4), wherein R.sub.1=tert-butyl, L.sub.1=pyridine, and L.sub.2=L.sub.3=L.sub.4=pivalic acid. Preferably, the compound of Formula II is selected from the following compound: compound 2, [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4), wherein R.sub.1=tert-butyl, L.sub.1=pyridine, L.sub.2=L.sub.3=L.sub.4=pivalic acid (or 2,2-dimethylpropionic acid, or trimethyl acetic acid, corresponding to R.sub.1COOH, wherein R.sub.1 is tert-butyl). Preferably, compound 2 is a single crystal of orthogonal system with space group of Pna21, cell parameters of a=19.059(3) , b=23.711(4) , c=19.416(4) , =90.00, =90.00, and =90.00, Z=4, and volume of 8774(3) .sup.3; and compound 2 has the structure as shown in the following Formula II-1: ##STR00018## wherein R.sub.1 is tert-butyl;

    3. A complex, characterized in that the complex is formed by the combination of two or more compounds of Formula II: ##STR00019## wherein, R.sub.1 is selected from the group consisting of H and C.sub.1-8 linear or branched alkyl; the four ligands L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are the same or different and are each independently selected from the group consisting of carboxylic acid molecules and derivatives thereof, pyridine, imidazole, pyrazine, quinoline, isoquinoline, bipyridine and derivatives thereof, or water molecule, alcohol molecules, ketones, nitriles (such as acetonitrile), esters and other exchangeable neutral small molecules. Preferably, the carboxylate anion (R.sub.1CO.sub.2.sup.) may be the anion of a carboxylic acid such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid and hexanoic acid. Preferably, R.sub.1 may be hydrogen (H), methyl (CH.sub.3), ethyl (C.sub.2H.sub.5), n-propyl (CH.sub.2CH.sub.2CH.sub.3), isopropyl (CH(CH.sub.3).sub.2), n-butyl ((CH.sub.2).sub.3CH.sub.3), isobutyl (CH(CH.sub.3)C.sub.2H.sub.5), tert-butyl (C(CH.sub.3).sub.3), n-pentyl ((CH.sub.2).sub.4CH.sub.3), isopentyl (CH.sub.2CH.sub.2CH(CH.sub.3).sub.2), and the like. Preferably, the complex is selected from the following ones: [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)], wherein R.sub.1=tert-butyl, L.sub.1=pyridine, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate; [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)], wherein R.sub.1=tert-butyl, L.sub.1=isoquinoline, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate. Preferably, the complex is selected from any of the following ones: complex 3, [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)], wherein R.sub.1=tert-butyl, L.sub.1=pyridine, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate. Complex 3 is a single crystal of monoclinic system with space group of P1 2.sub.1/c1, cell parameters of a=29.9019(5) , b=18.9368(3) , c=30.1980(4) , =90.00, =92.6590(10), and =90.00, Z=4, and volume of 17081.1(5) .sup.3. The [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)] part of the structure of complex 3 is shown in Formula II-1, and the [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)] part is shown in the following Formula II-2: ##STR00020## wherein R.sub.1 is tert-butyl; complex 4, [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)], wherein R.sub.1=tert-butyl, L.sub.1=isoquinoline, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate. The compound is a single crystal of triclinic system with space group of P-1, cell parameters of a=14.676(2) , b=25.313(3) , c=25.601(4) , =76.547(5), =87.559(6), and =73.153(6), Z=2, and volume of 8850(2) .sup.3. The [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)] part of the structure of complex 4 is shown in Formula II-3-1, and the [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)] part is shown in the following Formula II-3-2: ##STR00021## wherein R.sub.1 is tert-butyl; ##STR00022## wherein R.sub.1 is tert-butyl;

    4. A method for preparing the [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2).sub.6(R.sub.1CO.sub.2H).sub.3 compound represented by Formula I according to claim 1, characterized in that the method comprises the following steps: A solution of an acid (preferably an organic carboxylic acid), an oxidant, Mn.sup.2+ salts and a Sr.sup.2+ salt in a molar ratio of x:y:1:1 (x=10-120, y=1-10; preferably x=20-100, y=2-8) in acetonitrile is heated and reacted for 10-60 minutes to give a solution; the precipitate is removed off by filtration; and the filtrate is allowed to stand still for 1-6 days to give crystals. Preferably, the divalent manganese salt, i.e., Mn.sup.2+ salt, may be selected from various carboxylates containing Mn.sup.2+, wherein the carboxylate anion is (R.sub.1CO.sub.2.sup.), or may be such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the divalent manganese salt may also be Mn(ClO.sub.4).sub.2, MnCl.sub.2, MnSO.sub.4, Mn(NO.sub.3).sub.2, Mn(CF.sub.3SO.sub.3).sub.2. or other divalent manganese salts These salts may be the derivatives containing different numbers of crystal water molecules per formula unit of the carboxylic acid salt (the number of the crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the Sr.sup.2+ salt may be selected from various carboxylates of strontium, wherein the carboxylate anion is (R.sub.1CO.sub.2.sup.), or may be such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the Sr.sup.2+ salt may also be Sr(ClO.sub.4).sub.2, Sr(NO.sub.3).sub.2, Sr(CF.sub.3SO.sub.3).sub.2 or other strontium salts. These salts may be the derivatives containing different numbers of crystal water molecules per formula unit of the carboxylic acid salt (the number of crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the oxidant is preferably permanganate anionic oxidant, more preferably tetrabutylammonium permanganate ((C.sub.4H.sub.9).sub.4N.MnO.sub.4). Preferably, the acid is preferably an organic carboxylic acid, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, hexanoic acid and other carboxylic acids and derivatives thereof (preferably isobutyric acid, pivalic acid). Preferably, the acetonitrile solvent is used at a volume of about 60-100 mL acetonitrile per mmol strontium salt. Preferably, the reaction temperature is 60 to 90 C., for example, may be 70 to 80 C. Preferably, the reaction time may be 10 to 60 minutes, for example, 20 to 50 minutes.

    5. Use of the [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2).sub.6(R.sub.1CO.sub.2H).sub.3 compound of Formula I according to claim 1 as a precursor for the synthesis of a biomimetic [Mn.sub.4SrO.sub.4] water splitting catalyst. Preferably, the compound of Formula I according to claim 1, which is a [Mn.sub.3SrO.sub.4] cluster compound, is converted into a [Mn.sub.4SrO.sub.4] cluster compound in the presence of water in situ. Preferably, the compound of Formula I according to claim 1, which is a [Mn.sub.3SrO.sub.4] cluster compound, is converted into a [Mn.sub.4SrO.sub.4] cluster compound in the presence of water in situ, and the [Mn.sub.4SrO.sub.4] cluster compound catalyzes the oxygen-releasing reaction.

    6. A method for preparing the [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4) compound represented by Formula II according to claim 2, characterized in that the method comprises the following steps: Step 1: A solution of an acid (preferably an organic carboxylic acid), an oxidant, Mn.sup.2+ salts, Sr.sup.2+ salt and water in a molar ratio of x:y:1:1:z (x=10-120, y=1-10, z=0-20; preferably x=20-100, y=2-8, z=0-10) in acetonitrile is heated and reacted for 10-60 minutes to give a solution; the precipitate is removed off by filtration; and the filtrate is crystallized to give crystals, and is preferably crystallized at 0 C. to give crystals; Step 2: the crystals obtained in step 1 are dissolved in an ester solvent, and then organic ligands L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are added; a crude product is obtained after crystallization; and then the crude product is recrystallized with alkane and halogenated hydrocarbon to give the final product. Preferably, the product obtained in Step 2 may be subject to further process (for example, recrystallization) with an alkane, a cycloalkane or a halogenated hydrocarbon to give the final product. Preferably, the divalent manganese salt may be selected from various carboxylates containing Mn.sup.2, wherein the carboxylate anion (R.sub.1CO.sub.2.sup.) is as described in claim 2, or may be such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the divalent manganese salt may also be Mn(ClO.sub.4).sub.2, MnCl.sub.2, MnSO.sub.4, Mn(NO.sub.3).sub.2, and Mn(CF.sub.3SO.sub.3).sub.2 or other divalent manganese salts. These salts may be the derivatives containing different numbers of crystal water molecules per formula unit of the carboxylic acid salt (the number of the crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the Sr.sup.2+ salt may be selected from various carboxylates of strontium, wherein the carboxylate anion (R.sub.1CO.sub.2.sup.) is as described in claim 2, or may be such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the strontium salt may also be Sr(ClO.sub.4).sub.2, Sr(NO.sub.3).sub.2, Sr(CF.sub.3SO.sub.3).sub.2 or other strontium salts. These salts may be the derivatives containing different numbers of crystal water molecules per formula unit of the carboxylic acid salt (the number of crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the oxidant is preferably permanganate anionic oxidant, more preferably tetrabutylammonium permanganate ((C.sub.4H.sub.9).sub.4N.MnO.sub.4). Preferably, the acid is preferably an organic carboxylic acid, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, hexanoic acid and other carboxylic acids and derivatives thereof (preferably acetic acid, pivalic acid). Preferably, the acetonitrile solvent in Step 1 is used at a volume of about 60-100 mL acetonitrile per mmol strontium salt. This reaction can only be carried out in acetonitrile solvent, because the target compound cannot be obtained in either alcohol or other organic solvents. Preferably, the ester organic solvent used in the reaction of Step 2 may be an ester such as ethyl acetate, methyl acetate, or propyl propionate. The organic solvent used for the recrystallization of the product may be linear or branched alkanes and halogenated hydrocarbons and derivatives thereof such as n-hexane, isooctane, dichloroethane, and dichloromethane. Preferably, the organic ligands may be the same or different and are each independently selected from the group consisting of carboxylic acid molecules and derivatives thereof, pyridine, imidazole, pyrazine, bipyridine, isoquinoline and derivatives thereof, or water molecule, alcohol molecules, ketones, nitriles (such as acetonitrile), esters and other exchangeable neutral small molecules. Preferably, the reaction temperature is 60 to 90 C., for example, may be 70 to 80 C. Preferably, the reaction time may be 10 to 60 minutes, for example, 20 to 50 minutes.

    7. A method for preparing the complex according to claim 3, characterized in that the method comprises the following steps: Step 1: A solution of an acid (preferably an organic carboxylic acid), an oxidant, Mn.sup.2+ salts, Sr.sup.2+ salt and water in a molar ratio of x:y:1:1:z (x=10-120, y=1-10, z=0-20; preferably x=20-100, y=2-8, z=0-10) in acetonitrile is heated and reacted for 10-60 minutes to give a solution; the precipitate is removed off by filtration; and the filtrate is crystallized to give crystals, and is preferably crystallized at 0 C. to give crystals; Step 2: the crystals obtained in Step 1 are dissolved in an ester solvent, and organic ligands L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are added; and a crude product is obtained after crystallization; Step 3: optionally, the product obtained in Step 2 is subject to further process (such as rinsing or recrystallization with an alkane, a cycloalkane or a halogenated hydrocarbon) to give the final product. Preferably, the product is dissolved in an ester solvent before further processing. Preferably, the divalent manganese salt may be selected from various carboxylates containing Mn.sup.2, wherein the carboxylate anion is (R.sub.1CO.sub.2.sup.), or may be such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the divalent manganese salt may also be Mn(ClO.sub.4).sub.2, MnCl.sub.2, MnSO.sub.4, Mn(NO.sub.3).sub.2, Mn(CF.sub.3SO.sub.3).sub.2 or other divalent manganese salts. These salts may be the derivatives containing different numbers of crystal water (the number of the crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the Sr.sup.2+ salt may be selected from various carboxylates of strontium, wherein the carboxylate anion is (R.sub.1CO.sub.2.sup.), such as formate, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, pivalate, hexanoate and other carboxylate radicals as well as derivatives thereof (preferably acetate, pivalate); or the strontium salt may also be Sr(ClO.sub.4).sub.2, Sr(NO.sub.3).sub.2, Sr(CF.sub.3SO.sub.3).sub.2 or other strontium salts. These salts may be the derivatives containing different numbers of crystal water molecules per formula unit of the carboxylic acid salt (the number of crystal water n is 0-6, preferably 1-5 or 2-4). Preferably, the oxidant is preferably permanganate anionic oxidant, more preferably tetrabutylammonium permanganate ((C.sub.4H.sub.9).sub.4N.MnO.sub.4). Preferably, the acid is preferably an organic carboxylic acid, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, hexanoic acid and other carboxylic acids and derivatives thereof (preferably acetic acid, pivalic acid). Preferably, the acetonitrile solvent in Step 1 is used at a volume of about 60-100 mL acetonitrile per mmol strontium salt. This reaction can only be carried out in acetonitrile solvent, because the target compound cannot be obtained in either alcohol or other organic solvents. Preferably, the ester organic solvent used in the reaction of Step 2 may be an ester such as ethyl acetate, methyl acetate, or propyl propionate. The organic solvent used for the recrystallization of the product may be linear or branched alkanes and halogenated hydrocarbons and derivatives thereof such as n-hexane, isooctane, dichloroethane, and dichloromethane. Preferably, the organic ligands may be the same or different and are each independently selected from the group consisting of carboxylic acid molecules and derivatives thereof, pyridine, imidazole, pyrazine, bipyridine, isoquinoline and derivatives thereof, or water molecule, alcohol molecules, ketones, nitriles (such as acetonitrile), esters and other exchangeable neutral small molecules. Preferably, the reaction temperature is 60 to 90 C., for example, may be 70 to 80 C. Preferably, the reaction time may be 10 to 60 minutes, for example, 20 to 50 minutes.

    8. Use of the compound of Formula II according to claim 2 as a biomimetic water splitting catalyst. Preferably, the compound of Formula II is used to drive the catalytic splitting of water in the presence of an oxidant (which may be a stable oxidant or a photoinduced transient oxidant) to release oxygen.

    9. Use of the complex according to claim 3 as a biomimetic water splitting catalyst. Preferably, the complex is used to drive the catalytic splitting of water in the presence of an oxidant (which may be a stable oxidant or a photoinduced transient oxidant) to release oxygen.

    10. A water splitting catalyst comprising a [Mn4SrO4](R1CO2)8(L1)(L2)(L3)(L4) compound according to claim 2.

    11. A water splitting catalyst, comprising the complex according to claim 3.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0102] FIG. 1 shows the crystal structure of compound 1 as prepared in Example 1 of the present invention. For the sake of clarity, the hydrogen atom, the methyl of the tert-butyl and solvent molecules are all omitted.

    [0103] FIG. 2 shows the crystal structure of compound 2 as prepared in Example 2 of the present invention. For the sake of clarity, the hydrogen atom, the methyl of the tert-butyl and solvent molecules are all omitted.

    [0104] FIG. 3 shows the crystal structure of complex 3 as prepared in Example 3 of the present invention. For the sake of clarity, the hydrogen atom, the methyl of the tert-butyl and solvent molecules are all omitted. There are two [Mn.sub.4SrO.sub.4] cluster compounds in the figure, and they differ in that one neutral pivalic acid molecule on the strontium ion is replaced by one ethyl acetate molecule.

    [0105] FIG. 4 shows the crystal structure of complex 4 as prepared in Example 4 of the present invention. For the sake of clarity, the hydrogen atom, the methyl of the tert-butyl and solvent molecules are all omitted. There are two [Mn.sub.4SrO.sub.4] cluster compounds in the figure, and they differ in that one neutral pivalic acid molecule on the strontium ion is replaced by one ethyl acetate molecule.

    [0106] FIG. 5 shows the trace of the change in UV-Vis absorption spectrum of the interaction between compound 2 and water in Example 5 of the present invention.

    [0107] FIG. 6 shows the electron paramagnetic signal produced after the oxidization of compound 2 in Example 6 of the present invention. The data supports that the four Mn ions of compound 2 in ground state have valence states of +3, +3, +4 and +4, respectively.

    [0108] FIG. 7 shows the determination of the oxygen released during the spliting of water catalyzed by compound 2 in the presence of oxidant in Example 7 of the present invention.

    SPECIFIC MODE FOR CARRYING OUT THE INVENTION

    [0109] The present invention will be further illustrated with reference to the specific examples below. It should be understood that these examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. In addition, it should also be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present invention.

    EXAMPLE 1

    Compound 1 [Mn.SUB.3.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.6.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.3

    [0110] The preparation method was as follows:

    [0111] To a 100 ml round bottom flask were added tetrabutylammonium permanganate (Bu.sup.n.sub.4N.MnO.sub.4, 4 mmol), manganese acetate (Mn(CH.sub.3CO.sub.2).sub.2, 1 mmol), strontium acetate (Sr(CH.sub.3CO.sub.2).sub.2, 1 mmol) and pivalic acid ((CH.sub.3).sub.3CCO.sub.2H, 40 mmol). After continuous reaction in acetonitrile at 80 C. for 25 min, the reaction was stopped. The precipitate, which was of a small amount, was removed off by filtration. The resulted brown mother liquor was allowed to stand still at 0 C. for 1-6 days and brown crystals were precipitated out. The resulted crystals were collected and dissolved in n-hexane, and dried under vacuum, with the yield of 60% (according to the mole numbers of Sr ions).

    [0112] Compound 1 has a structural formula of [Mn.sub.3SrO.sub.4](R.sub.1CO.sub.2).sub.6(R.sub.1CO.sub.2H).sub.3, wherein R.sub.1=tert-butyl.

    [0113] That is, compound 1 has a structural formula of [Mn.sub.3SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.6(C.sub.5H.sub.9O.sub.2H).sub.3 and a molecular formula of C.sub.45H.sub.84Mn.sub.3O.sub.22Sr. Theoretical values of elemental analysis are: C, 43.96; H, 6.89; and experimental values are: C, 44.01; H, 6.84. Compound 1 is a single crystal of trigonal system with space group of R-3c, cell parameters of a=10.6575(15) , b=10.6575(15) , c=87.917(18) , =90.00, =90.00, and =120.00, Z=6, and volume of 8648(3) .sup.3.

    [0114] Compound 1 has a chemical structure as shown in Formula I-1 below, determined specific single crystal parameters as shown in Table 1, and a crystal space structure as shown in FIG. 1.

    ##STR00010## [0115] wherein R.sub.1=tert-butyl;

    EXAMPLE 2

    Compound 2 [Mn.SUB.4.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.8.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.3.(C.SUB.5.H.SUB.5.N)

    [0116] The preparation method was as follows:

    [0117] The first step was the synthesis of the precursor of compound 2. To a 100 ml round bottom flask were added tetrabutylammonium permanganate (Bu.sup.n.sub.4N.MnO.sub.4, 4 mmol), manganese acetate (Mn(CH.sub.3CO.sub.2).sub.2, 1 mmol), strontium acetate (Sr(CH.sub.3CO.sub.2).sub.2, 1 mmol), pivalic acid ((CH.sub.3).sub.3CCO.sub.2H, 40 mmol) and water (H.sub.2O, 1 mmol). After continuous reaction in acetonitrile at 80 C. for 25 min, the reaction was stopped. The precipitate, which was of a small amount, was removed off by filtration. The resulted brown mother liquor was allowed to stand still at 0 C. for 1-2 weeks and brown crystals were precipitated out.

    [0118] The second step was the reaction with pyridine. The crystals obtained in the first step were collected and dissolved in ethyl acetate. 2% (volume ratio) of pyridine was added, and after 1-2 weeks, brown crystals were precipitated out. The resulted crystals were collected and dissolved in n-hexane. The undissolved substance, which was of a small amount, was removed off, and the solution was subject to recrystallization. After 1 week, brown crystals were precipitated out and dried under vacuum. The yield was 12% (according to the mole numbers of Sr.sup.2+ ions).

    [0119] Compound 2 has a structural formula of [Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4), wherein R.sub.1=tert-butyl, L.sub.1=pyridine, and L.sub.2=L.sub.3=L.sub.4=pivalic acid.

    [0120] That is, compound 2 has a structural formula of [Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.5H.sub.9O.sub.2H).sub.3(C.sub.5H.sub.5N).(C.sub.6H.sub.14).sub.1.5 (note: the n-hexane is a solvent molecule), and a molecular formula of C.sub.69H.sub.128Mn.sub.4NO.sub.26Sr. Theoretical values of elemental analysis are: C, 48.89; H, 7.61; N, 0.83; and experimental values are: C, 49.00; H, 7.51; N, 0.70. Compound 2 is a single crystal of orthogonal system with space group of Pna21, cell parameters of a=19.059(3) , b=23.711(4) , c=19.416(4) , =90.00, =90.00, and =90.00, Z=4, and volume of 8774(3) .sup.3.

    [0121] Compound 2 has a chemical structure as shown by Formula II-1 below, determined specific single crystal parameters as shown in Table 2, and a crystal space structure as shown in FIG. 2.

    ##STR00011## [0122] wherein R.sub.1=tert-butyl;

    EXAMPLE 3

    Complex 3 [[Mn.SUB.4.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.8.(C.SUB.5.H.SUB.5.N).SUB.1.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.3.].[[Mn.SUB.4.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.8.(C.SUB.5.H.SUB.5.N).SUB.1.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.2.(C.SUB.2.H.SUB.5.O.SUB.2.CCH.SUB.3.).SUB.1.]

    [0123] The preparation method was as follows:

    [0124] 0.100 g compound 2 was weighed and dissolved in ethyl acetate. The mixture was allowed to stand still at room temperature for 1-3 weeks and slender brown crystals were precipitated out. The crystals were rinsed with cyclohexane and then vacuum dried. The yield was 70% (according to the mole numbers of Sr.sup.2+ ions).

    [0125] Complex 3 has a structural formula of [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8](L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8](L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4*)], wherein R.sub.1=tert-butyl, L.sub.1=pyridine, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate.

    [0126] That is, complex 3 has a structural formula of [[Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.5H.sub.5N).sub.1(C.sub.5H.sub.9O.sub.2H).sub.3].[[Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.5H.sub.5N).sub.1(C.sub.5H.sub.9O.sub.2H).sub.2(C.sub.2H.sub.5O.sub.2CCH.sub.3).sub.1], and a molecular formula of C.sub.119H.sub.212Mn.sub.8N.sub.2O.sub.52Sr.sub.2. Theoretical values of elemental analysis are: C, 45.84; H, 6.85; N, 0.90; and experimental values are: C, 45.82; H, 6.81; N, 1.21. Complex 3 is a single crystal of monoclinic system with space group of P1 2.sub.1/c1, cell parameters of a=29.9019(5) , b=18.9368(3) , c=30.1980(4) , =90.00, =92.6590(10), and =90.00, Z=4, and volume of 17081.1(5) .sup.3. Complex 3 has a chemical structure of [[Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.5H.sub.5N).sub.1(C.sub.5H.sub.9O.sub.2H).sub.2(C.sub.2H.sub.5O.sub.2CCH.sub.3).sub.1] as shown by Formula II-2 below, determined specific single crystal parameters as shown in Table 3, and a crystal space structure as shown in FIG. 3.

    ##STR00012## [0127] wherein R.sub.1=tert-butyl;

    EXAMPLE 4

    Complex 4 [[Mn.SUB.4.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.8.(C.SUB.9.H.SUB.7.N).SUB.1.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.3.].[[Mn.SUB.4.SrO.SUB.4.](C.SUB.5.H.SUB.9.O.SUB.2.).SUB.8.(C.SUB.9.H.SUB.7.N).SUB.1.(C.SUB.5.H.SUB.9.O.SUB.2.H).SUB.2.(C.SUB.2.H.SUB.5.O.SUB.2.CCH.SUB.3.).SUB.1.]

    [0128] The preparation method was as follows:

    [0129] The first step was the synthesis of the precursor of complex 4. To a 100 ml round bottom flask were added tetrabutylammonium permanganate (Bu.sup.n.sub.4N.MnO.sub.4, 4 mmol), manganese acetate (Mn(CH.sub.3CO.sub.2).sub.2, 1 mmol), strontium acetate (Sr(CH.sub.3CO.sub.2).sub.2, 1 mmol) and pivalic acid ((CH.sub.3).sub.3CCO.sub.2H, 40 mmol). After continuous reaction in acetonitrile at 80 C. for 25 min, the reaction was stopped. The precipitate, which was of a small amount, was removed off by filtration. The resulted brown mother liquor was allowed to stand still at 0 C. for 1-2 weeks and brown crystals were precipitated out.

    [0130] The second step was the reaction with isoquinoline. The crystals obtained in the first step were collected and dissolved in ethyl acetate. 1% (volume ratio) isoquinoline was added for recrystallization. After 1-2 weeks, black crystals were collected, rinsed with cyclohexane and vacuum dried. The yield was 40% (according to the mole numbers of Sr.sup.2+ ions).

    [0131] Complex 4 has a structural formula of [[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)].[[Mn.sub.4SrO.sub.4](R.sub.1CO.sub.2).sub.8(L.sub.1)(L.sub.2)(L.sub.3)(L.sub.4)], wherein R.sub.1=tert-butyl, L.sub.1=isoquinoline, L.sub.2=L.sub.3=L.sub.4=pivalic acid, and L.sub.4*=ethyl acetate.

    [0132] That is, complex 4 has a structural formula of [[Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.9H.sub.7N).sub.1(C.sub.5H.sub.9O.sub.2H).sub.3].[[Mn.sub.4SrO.sub.4](C.sub.5H.sub.9O.sub.2).sub.8(C.sub.9H.sub.7N).sub.1(C.sub.5H.sub.9O.sub.2H).sub.2(C.sub.2H.sub.5O.sub.2CCH.sub.3).sub.1], and a molecular formula of C.sub.132H.sub.226Mn.sub.8N.sub.2O.sub.54Sr.sub.2. Complex 4 is a single crystal of triclinic system with space group of P-1, cell parameters of a=14.676(2) , b=25.313(3) , c=25.601(4) , =76.547(5), =87.559(6), and =73.153(6), Z=2, and volume of 8850(2) .sup.3.

    [0133] Complex 4 has a chemical structure as shown by Formulas II-3-1 and II-3-2 below, determined specific single crystal parameters as shown in Table 4, and a crystal space structure as shown in FIG. 4.

    ##STR00013## [0134] wherein R.sub.1=tert-butyl;

    ##STR00014## [0135] wherein R.sub.1=tert-butyl;

    EXAMPLE 5

    Trace of the UV-Vis Spectrum of the Interaction Between Compound 2 and Water

    [0136] To a colorimetric cell was added 1 mL solution of 25 M compound 2 in acetonitrile. Using 1 mL pure acetonitrile as reference, the absorption spectrum was determined in Hitachi U-3900 spectrophotometer type UV-Vis spectrometer (see FIG. 5). This compound had the maximum absorption at 250 nm. With the addition of water (0%, 0.15%, 0.35%, 0.55% and 1.05% water was added respectively), the absorption spectrum changed significantly. Specifically, the absorption at 250 nm decreased significantly, while the absorption at 400 nm increased, indicating that water molecules interacted with compound 2. As compared with [Mn.sub.4CaO.sub.4] cluster compounds, the sensitivity of [Mn.sub.4SrO.sub.4] cluster compounds to water was significantly reduced. The absorption peak of [Mn.sub.4SrO.sub.4] cluster compound at 250 nm was only reduced by 20% when there existed 1% water, whereas the absorption peak of the corresponding [Mn.sub.4CaO.sub.4] cluster compound at 250 nm was reduced by more than 60% when there existed 1% water, indicating that a small amount of water has little effect on the spectrum of [Mn.sub.4SrO.sub.4] but has a greater effect on the spectrum of [Mn.sub.4CaO.sub.4] cluster compounds. [Mn.sub.4CaO.sub.4] cluster compounds belongs to water extremely sensitive substances, and the sensitivity leads to reduced stability and therefore limited the application thereof. To the contrary, the [Mn.sub.4SrO.sub.4] cluster compounds newly synthesized and discovered in the present invention were much more stable than [Mn.sub.4CaO.sub.4] cluster compounds and had a wide application prospect as water splitting catalyst.

    EXAMPLE 6

    Electron Paramagnetic Resonance of Compound 2 for Detecting the Valence State of Mn Ions in the Compound

    [0137] Compound 2 (1 mM) was dissolved in dichloroethane, and then 0.5 mM oxidant [Fe(Phen).sub.3](PF.sub.6).sub.3 (wherein Phen=phenanthroline) was added. The mixture was then rapidly frozen to 77K and the electron paramagnetic signals were detected with Bruker E500 electron paramagnetic resonance instrument at 7K (see FIG. 6). The multiple peak paramagnetic signal at g=2.0 was clearly seen. The occurrence of this signal indicated that after oxidization of the compound, the valence states of the four manganese ions were +3, +4, +4 and +4, respectively. Thus it could be inferred that the valence states of the four Mn ions in the ground state (i.e., the stable state before oxidation) of the compound were +3, +3, +4 and +4, respectively.

    EXPERIMENTAL EXAMPLE 7

    Determination of the Oxygen Released During the Water Splitting Catalyzed by Compound 2 in the Presence of an Oxidant

    [0138] The activity of releasing oxygen during the catalytic water splitting was determined on a Clark-type oxygen electrode (FIG. 7). A rapid release of oxygen to saturation was observed with the addition of 500 M of compound 2 to an aqueous solution containing an oxidant (hydrogen peroxide, 0.1 M), whereas no visible release of oxygen was observed with the addition of the reference compound (Mn(ClO.sub.4).sub.2). The arrow in the figure showed the loading position of the sample. FIG. 7 indicated that compound 2 had catalytic activity of catalyzing the splitting of water to release oxygen.

    [0139] The embodiments of the present invention have been described above. However, this invention is not limited to the above embodiments. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.