JP7669016B2 - Method for producing polynuclear metal compounds - Google Patents

Description

The present invention relates to a method for producing a polynuclear metal compound. More specifically, the present invention relates to a polynuclear metal compound that may be suitable for use as a catalyst, medicine, functional material, etc., and a method for producing the same.

Polyoxometalates are attractive substances in a variety of fields, including catalysis, medicine, and functional materials, due to their high stability and easily adjustable chemical and physical properties. For this reason, there is a demand for the development of polyoxometalates with even newer structures.

Some polyoxometalates have unstable structures derived from defective polyoxometalates. For example, molybdenum oxide clusters are extremely unstable compared to tungsten oxide clusters, which have been widely studied. As a result, there are few reported research projects based on molybdenum oxide clusters, and in particular, there are no examples of their application to the structural design of polynuclear metal compounds.

As a report on the stabilization of normally unstable defect-type polyoxometalates, it has been reported that a stable anionic _{polyoxometalate} [ _PMo9O31 (py) ₃ ] ^3- (I) can be obtained by coordinating pyridine (py) to a phosphorus molybdenum oxide cluster [ _PMo9O34 ] ^9- in an organic solvent. It has also been reported that a dimeric polyoxometalate ( _II ) can be obtained from anionic polyoxometalate I and 4,4'-bipyridine, and a tetrameric polyoxometalate (III) can be obtained from anionic polyoxometalate I and 5,10,15,20-tetra(4-pyridyl)porphyrin (see Non-Patent Document 1).

Chifeng Li et al. and 3 others, Journal of the American Chemical Society (USA), 2019, Vol. 141, pp. 7687-7692

As described above, there is a need for further development of polyoxometalates with new structures, and it has been desirable to make better use of the diverse properties that are exhibited depending on the type and coordination state of the metal atoms.
The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a novel metal compound which is promising as a catalyst or the like.

The present inventors have investigated methods for producing metal compounds and discovered that a novel polynuclear metal compound can be obtained by reacting a polyoxometalate compound having a structure in which a non-shared electron pair-containing compound is introduced into the defective structural site of a defective polyoxometalate containing a specific polyatom with a compound containing a metal atom other than the heteroatom and polyatom, thereby arriving at the present invention.

That is, the present invention is a method for producing a polynuclear metal compound having a structure in which a metal atom other than a heteroatom and a polyatom is introduced into the defective structural site of a polyoxometalate compound, and the method includes a step of reacting a polyoxometalate compound (A) having a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to the heteroatom via an oxygen atom and an unshared electron pair-containing compound is introduced into the defective structural site with a compound (B) containing a metal atom other than a heteroatom and a polyatom.

The present invention also relates to a polynuclear metal compound having a structure in which a metal atom other than a heteroatom and a polyatom is introduced into a defective structural site of a polyoxometalate compound, and the polynuclear metal compound is also a polynuclear metal compound having a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to the heteroatom via an oxygen atom.
The present invention will be described in detail below.
In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

<Method of producing polynuclear metal compound of the present invention>
The method for producing a polynuclear metal compound of the present invention includes a step of reacting a polyoxometalate compound (A) having a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to a heteroatom via an oxygen atom and an unshared electron pair-containing compound is introduced into the defective structural site, with a compound (B) containing a metal atom different from the heteroatom and the polyatom.
In this specification, a compound having two or more metal atoms different from heteroatoms and polyatoms is referred to as a polynuclear metal compound. The metal atoms may be of one type or of two or more types.
First, the raw material compounds and preferred reaction conditions in the reaction steps will be described below.

The polyatom in the polyoxometalate compound (A) is preferably at least one selected from the group consisting of Mo, V, Nb, and Ta, and more preferably Mo.

The heteroatom in the polyoxometalate compound (A) is preferably at least one selected from the group consisting of Si, P, Al, S, Ge, As, and Se. Among these, Si and/or P are more preferred, and P is even more preferred.

The polyoxometalate compound (A) has a structure in which a non-shared electron pair-containing compound is introduced at the defective structure site, meaning that the oxygen atom or a group containing an oxygen atom (e.g., -OH ₂ group) at the defective structure site is replaced with an atom having a non-shared electron pair in the non-shared electron pair-containing compound. It is not necessary that the compound has actually undergone a substitution reaction, as long as it has a similar structure. The number of defective structure sites in the polyoxometalate compound (A) is usually two or more, and the polyoxometalate compound (A) is preferably a two-deficient type or a three-deficient type. For example, the polyoxometalate compound (A) may have a structure in which a non-shared electron pair-containing compound is introduced at least one of the two defective structure sites, or may have a structure in which a non-shared electron pair-containing compound is introduced at least one of the three defective structure sites. In particular, the polyoxometalate compound (A) preferably has a structure in which a non-shared electron pair-containing compound is introduced into at least two defective structure sites, and more preferably has a structure in which a non-shared electron pair-containing compound is introduced into all defective structure sites.
The polyoxometalate compound (A) has a structure in which a non-shared electron pair-containing compound is introduced into the defective structure site, and therefore is stable in a solvent, and side reactions are sufficiently suppressed, and isomerization is thought to be suppressed. By subjecting such a polyoxometalate compound (A) to the above reaction step, a novel polynuclear metal compound can be produced.

The unshared electron pair-containing compound in the polyoxometalate compound (A) is a compound containing an atom having an unshared electron pair, and the compound replaces the easily removable oxygen atom or group containing an oxygen atom at the defective structure site, thereby contributing to the stabilization of the polyoxometalate. In a structure in which the unshared electron pair-containing compound is introduced at the defective structure site, the unshared electron pair-containing compound may be introduced while maintaining the structure of the raw material unshared electron pair-containing compound as it is, or may be introduced in a form in which the structure of the raw material unshared electron pair-containing compound is changed, but it is preferable that the unshared electron pair-containing compound is introduced while maintaining the structure of the raw material unshared electron pair-containing compound as it is.

Suitable examples of the atom having an unshared electron pair contained in the unshared electron pair-containing compound include a nitrogen atom, an oxygen atom, a phosphorus atom, and a sulfur atom, and among these, a nitrogen atom is more preferred. That is, the unshared electron pair-containing compound is preferably a nitrogen atom-containing compound.
Suitable examples of the nitrogen atom-containing compound include primary amines, secondary amines, and nitrogen-containing heterocyclic aromatic compounds, with nitrogen-containing heterocyclic aromatic compounds being more preferred.
Preferred examples of the nitrogen-containing heterocyclic aromatic compound include pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, etc. Among these, pyridine is more preferred.
In this specification, the unshared electron pair-containing compound introduced into the defective structural site of the polyoxometalate compound (A) can be rephrased as an unshared electron pair-containing group, and the nitrogen-containing heterocyclic aromatic compound introduced into the defective structural site can be rephrased as a nitrogen-containing heterocyclic aromatic group.

The polyoxometalate compound (A) generally forms a salt, and the cation (counter cation) for forming the salt may be either an inorganic cation or an organic cation.
Examples of inorganic cations include alkali metal cations, alkaline earth metal cations, transition metal cations, typical metal cations, protons, ammonium, etc., and one or more of these can be used.
The organic cation includes organic ammonium, organic phosphonium, etc., and one or more of these can be used.
Among these, the counter cation is preferably an organic cation.
The organic cation preferably has 4 to 48 carbon atoms, more preferably 4 to 40 carbon atoms, and even more preferably 4 to 30 carbon atoms.

The organic ammonium is preferably a quaternary organic ammonium. Examples of the quaternary organic ammonium include tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tributylmethylammonium, trioctylmethylammonium, trilaurylmethylammonium, benzyltrimethylammonium, benzyltriethylammonium, benzyltributylammonium, cetylpyridinium, and the like. One or more of these can be used.

As the organic phosphonium, a quaternary organic phosphonium is preferable. Examples of the quaternary phosphonium include tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium, tetraphenylphosphonium, ethyltriphenylphosphonium, and benzyltriphenylphosphonium, and one or more of these can be used.

In the manufacturing method of the present invention, the metal atom in the compound (B) having a metal atom different from the heteroatom and polyatom is preferably at least one selected from the group consisting of 3d transition metal atoms, 4d transition metal atoms, 5d transition metal atoms, and rare earth elements. In other words, the metal atom different from the heteroatom and polyatom is preferably at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
In the production method of the present invention, a stable polyoxometalate compound (A) is used as a raw material, and by reacting this with the above-mentioned compound (B), it is possible to appropriately introduce metal atoms derived from compound (B) that are known as heterometals in polyoxometalates.

Examples of the 3d transition metal atom include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Among them, V, Mn, Fe, Co, and Ni are preferred, and V and Mn are more preferred.
Examples of the 4d transition metal atom include Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag, and among these, Y, Ru, Rh, Pd, and Ag are preferred.
Examples of the 5d transition metal atom include Hf, Ta, W, Re, Os, Ir, Pt, and Au, and among these, Hf, Ta, and W are preferred.
Examples of the rare earth elements include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and among these, Ce, Sm, Eu, Gd, Tb, and Dy are preferred.

The compound (B) having a metal atom different from the heteroatom and polyatom preferably contains at least one group selected from the group consisting of a carboxylate group, a trifluoromethanesulfonate group, and an acetylacetonate group. Among these, the acetylacetonate group is more preferred.

Examples of the compound (B) having a metal atom different from the heteroatom and polyatom include, for example, vanadyl acetylacetonate, manganese acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, palladium acetylacetonate, silver acetylacetonate, lanthanum acetylacetonate, and terbium acetylacetonate, and one or more of these can be used.

The manufacturing method of the present invention is not particularly limited as long as it includes a step of reacting the above-mentioned specific polyoxometalate compound (A) with a compound (B) containing a metal atom different from the heteroatom and polyatom. A suitable manufacturing method includes mixing the polyoxometalate compound (A) and the compound (B) containing a metal atom different from the heteroatom and polyatom in an organic solvent or a solvent containing an organic solvent when reacting the polyoxometalate compound (A) and the compound (B) containing a metal atom different from the heteroatom and polyatom. Here, the polyoxometalate compound (A) can be added as a powder or as a solution to a liquid in which the compound (B) having a metal atom different from the heteroatom and polyatom is dispersed or dissolved, to produce the polynuclear metal compound. The polyoxometalate compound (A) and the compound (B) having a metal atom different from the heteroatom and polyatom may be added to the solvent at the same time. The polyoxometalate compound (A) may be added all at once or gradually. The polynuclear metal compound may be produced in a single step or in multiple steps. For example, a method may be used in which the product is once removed without mixing a portion of the predetermined amount of polyoxometalate compound (A) or compound (B), the product is redissolved in a solvent, and then the remaining polyoxometalate compound (A) or compound (B) is mixed.

The molar ratio of polyoxometalate compound (A) to compound (B) in the above reaction step may be appropriately set depending on the number of metal atoms different from the heteroatoms and polyatoms contained in compound (B) and the number of such metal atoms to be introduced into one polyoxometalate compound (A), but is preferably 1:1 to 1:10, more preferably 2:3 to 1:9, and even more preferably 1:2 to 1:8.

In the above reaction step, it is also preferable to react the polyoxometalate compound (A) with the compound (B) so that the ratio of the number of unshared electron pair-containing compounds contained in the polyoxometalate compound (A) to the number of metal atoms other than the heteroatoms and polyatoms contained in the compound (B) is, for example, 1:10 to 10:1. This ratio is more preferably 1:5 to 5:1, and even more preferably 1:2 to 2:1.

In the above reaction step, the mixing time of the polyoxometalate compound (A) and the compound (B) is preferably 1 minute or more from the viewpoint of sufficiently introducing the compound (B) into the defective structural sites of the polyoxometalate compound (A). The mixing time is more preferably 10 minutes or more, and even more preferably 20 minutes or more. The mixing time is preferably 72 hours or less. More preferably, the mixing time is 48 hours or less, even more preferably 24 hours or less, and particularly preferably 3 hours or less.
The mixing time mainly means the time during which the polyoxometalate compound (A) and the compound (B) coexist and are mixed in a homogeneous solution, and refers to the time from the time when the polyoxometalate compound (A) is added to the solution containing the compound (B) to the time when an inorganic salt, an organic salt, or a poor solvent is added to precipitate the polynuclear metal compound. The mixing can be performed using a commercially available stirrer or the like. If impurities precipitate during mixing, they can be removed by filtration or the like as necessary. The setting of the mixing time is one of the important factors that determine the structure of the polynuclear metal compound, and may be appropriately set within the above range depending on the type of element introduced by the compound (B). The polynuclear metal compound can be purified by recrystallization or the like. It can also be prepared and stored in the system without isolation, and used as a catalyst or the like as it is.

In the above reaction step, the temperature at which the polyoxometalate compound (A) and the compound (B) are mixed is preferably 0° C. or higher, more preferably 10° C. or higher, and even more preferably 15° C. or higher. The temperature is preferably 150° C. or lower, more preferably 100° C. or lower, and even more preferably 60° C. or lower.
The above reaction step can be carried out under increased pressure, normal pressure, or reduced pressure.

An acid may be added during or after mixing of polyoxometalate compound (A) and compound (B) as described below. Also usable is a method in which polyoxometalate compound (A) or compound (B) is mixed to introduce an element derived from compound (B) into polyoxometalate compound (A), and then polyoxometalate compound (A) or compound (B) is further added to obtain a polynuclear metal compound.
Alternatively, a method can be used in which a compound obtained by introducing an element derived from compound (B) into one polyoxometalate compound (A) is dissolved in a solvent to obtain a compound, and then a compound obtained by introducing an element derived from compound (B) into one polyoxometalate compound (A) is added to the solution, and a poor solvent is added thereto to obtain a polynuclear metal compound.

The solvent preferably contains an organic solvent. The solvent containing an organic solvent may contain other components as long as it contains an organic solvent, but one preferred form of the solvent containing an organic solvent is a mixed solvent of an organic solvent and water.
The volume ratio of the organic solvent to water in the above solvent is not particularly limited, but is preferably 100:0 to 30:70, more preferably 100:0 to 50:50, and even more preferably 100:0 to 70:30.

The organic solvent is not particularly limited, but may be one or more of the following: acetone, acetonitrile, benzonitrile, methanol, ethanol, propanol, butanol, chloroform, dichloroethane, hexane, octane, benzene, toluene, xylene, ethyl acetate, butyl acetate, propylene carbonate, diethyl ether, dibutyl ether, diisopropyl ether, dioxane, tetrahydrofuran, cyclopentyl methyl ether, methyl ethyl ketone, methyl isobutyl ketone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, nitromethane, etc. Among these, acetone, acetonitrile, benzonitrile, methanol, ethanol, butanol, dichloroethane, hexane, octane, toluene, xylene, ethyl acetate, butyl acetate, propylene carbonate, diethyl ether, dioxane, tetrahydrofuran, cyclopentyl methyl ether, methyl ethyl ketone, methyl isobutyl ketone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and nitromethane are preferred, and acetone, acetonitrile, benzonitrile, methanol, ethanol, butanol, dichloroethane, toluene, xylene, ethyl acetate, butyl acetate, propylene carbonate, diethyl ether, dioxane, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, dimethylformamide, dimethyl sulfoxide, and nitromethane are more preferred. Even more preferred are acetone, acetonitrile, benzonitrile, butanol, toluene, ethyl acetate, butyl acetate, propylene carbonate, dichloroethane, diethyl ether, methyl isobutyl ketone, dimethylformamide, dimethyl sulfoxide, and nitromethane.

The poor solvent may be one or more of hexane, octane, benzene, toluene, xylene, ethyl acetate, butyl acetate, propylene carbonate, diethyl ether, dibutyl ether, diisopropyl ether, dioxane, tetrahydrofuran, cyclopentyl methyl ether, methyl ethyl ketone, methyl isobutyl ketone, dichloroethane, chloroform, etc.

The volume of the solvent is preferably 1 mL or more per 1 mmol of polyoxometalate compound (A). More preferably, it is 10 mL or more, and even more preferably, it is 20 mL or more. Also, it is preferably 5000 mL or less. More preferably, it is 2500 mL or less, and even more preferably, it is 1000 mL or less.

As described above, an acid may be further mixed when or after polyoxometalate compound (A) and compound (B) are mixed, and preferably, the acid is mixed after polyoxometalate compound (A) and compound (B) are mixed.
As the acid, inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and boric acid, as well as organic acids such as p-toluenesulfonic acid, acetic acid, benzoic acid, and malonic acid can be used.
The amount of the acid used is preferably 0.01 moles or more, more preferably 0.1 moles or more, and even more preferably 1 mole or more, relative to 1 mole of the polyoxometalate compound (A), and is preferably 100 moles or less, more preferably 50 moles or less, and even more preferably 10 moles or less.

The manufacturing method of the present invention may be a stepwise manufacturing method in which a polynuclear metal compound is manufactured by the above-mentioned method, and then another operation is performed on the polynuclear metal compound. By such a multistep manufacturing method, it is possible to manufacture a polynuclear metal compound containing two or more types of metal atoms other than heteroatoms and polyatoms, or a polynuclear metal compound having a specific structure.

Also suitable is a multi-step manufacturing method in which the obtained polynuclear metal compound is dissolved in an organic solvent, a counter cation is added and stirred, the solvent is removed, and the resulting solid is recrystallized in the presence of a specific organic solvent.

Also suitable is a multi-step manufacturing method in which a polynuclear metal compound having one type of metal atom different from heteroatoms and polyatoms is manufactured, then the polynuclear metal compound is dissolved in an organic solvent, and a compound of a metal atom different from the metal atom possessed by the polynuclear metal compound is added to the obtained solution and stirred to manufacture a polynuclear metal compound having two or more types of metal atoms as metal atoms different from heteroatoms and polyatoms. By such a manufacturing method, a polynuclear metal compound having two or more types of metal atoms different from heteroatoms and polyatoms can be manufactured.

The manufacturing method of the present invention may further include a step of reacting a compound having a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to a heteroatom via an oxygen atom with a non-shared electron pair-containing compound to obtain the above-mentioned polyoxometalate compound (A).

The polynuclear metal compound of the present invention can be suitably obtained by the manufacturing method of the present invention. The polynuclear metal compound of the present invention will be described below.

<Polynuclear metal compound of the present invention>
The polynuclear metal compound of the present invention is a polynuclear metal compound having a structure in which a metal atom other than a heteroatom and a polyatom is introduced into the defective structural site of a polyoxometalate compound, and the polynuclear metal compound has a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to the heteroatom via an oxygen atom.
In addition, when it is not possible to distinguish whether the two or more types of metal atoms contained in a polynuclear metal compound are polyatoms or metal atoms different from the heteroatoms and polyatoms introduced into the defective structure sites, one of them can be a polyatom and the others can be metal atoms different from the heteroatoms and polyatoms.

The polynuclear metal compound of the present invention has a structure in which a metal atom other than a heteroatom and a polyatom is introduced into the defective structure site of the polyoxometalate compound, which usually means that the compound has a structure in which an atom such as an oxygen atom in the defective structure site is directly or indirectly bonded to a metal atom other than a heteroatom and a polyatom. In particular, it is preferable that the oxygen atom in the defective structure site is directly bonded to a metal atom other than a heteroatom and a polyatom. The number of defective structure sites in the polyoxometalate compound is usually two or more, and it is preferable that the polyoxometalate compound is a two-deficient type or a three-deficient type. For example, the polyoxometalate compound may be originally a two-deficient type having a structure in which a metal atom other than a heteroatom and a polyatom is introduced into each of the two defective structure sites, or may be originally a three-deficient type having a structure in which a metal atom other than a heteroatom and a polyatom is introduced into at least two of the three defective structure sites. The polyoxometalate compound generally has a structure in which a metal atom different from a heteroatom and a polyatom is introduced into at least two defect structure sites, and preferably has a structure in which a metal atom different from a heteroatom and a polyatom is introduced into all defect structure sites.

The polynuclear metal compound of the present invention contains a heteropolyoxometalate anion in its crystal structure. The polyatom in the heteropolyoxometalate anion is at least one selected from the group consisting of Mo, V, Nb, and Ta. The heteroatom is preferably at least one selected from the group consisting of Si, P, Al, S, Ge, As, and Se. Such a heteropolyoxometalate anion has a crystal structure called a Keggin type, in which 9 to 11 polyatoms are coordinated to the heteroatom via oxygen.

When the polyoxometalate compound is of the two-deficient type, the heteropolyoxometalate anion is represented by the following general formula (1):
[QZ ₁₀ O _j ] ^k- (1)
(wherein Q represents a heteroatom; Z is the same or different and represents a polyatom selected from Mo, V, Nb, or Ta; j and k are positive numbers, and k is determined by the valences of Q and Z).
When the polyoxometalate compound is a three-deficient type, the heteropolyoxometalate anion is represented by the following general formula (2):
[QZ ₉ O _m ] ^n- (2)
(wherein Q represents a heteroatom; Z is the same or different and represents a polyatom selected from Mo, V, Nb, or Ta; m and n are positive numbers, and n is determined by the valences of Q and Z).

In the general formulas (1) and (2), a Keggin type heteropolyoxometalate anion in which Z is Mo is more preferred.
That is, in the polynuclear metal compound of the present invention, the polyatom is Mo, which is also one of the preferred embodiments of the present invention.

Furthermore, the Keggin type heteropolyoxometalate anion preferably has an isomeric structure of α, β, or γ. In the case of the two-deficient type, examples of the Keggin type heteropolyoxometalate anion include [α-PMo ₁₀ O 36 ] ^7- and/or [β-PMo 10 O ₃₆ ] 7- and/or [γ-PMo ₁₀ O ₃₆ ] ^7- , or [α-SiMo ₁₀ O ₃₆ ] ^8- and/or [β-SiMo ₁₀ O ₃₆ ] ^8- and/or [γ-SiMo ₁₀ O ₃₆ ] ^8- , or [α-GeMo ₁₀ O ₃₆ ] ^8- and/or [β-GeMo ₁₀ O ₃₆ ] ^8- and/or [γ-GeMo ₁₀ O ₃₆ ] ^8- , ^where Q in general formula _{( 1} ) is P, Si, or Ge. More preferred are [γ-PMo ₁₀ O ₃₆ ] ⁷⁻ , [γ-SiMo ₁₀ O ₃₆ ] ⁸⁻ and [γ-GeMo ₁₀ O ₃₆ ] ⁸⁻ .
In the case of the triple-deficient type, examples of the Keggin type heteropolyoxometalate anion include [α-PMo ₉ O 34 ] ^9- and/or [β-PMo 9 O ₃₄ ] 9- and/or [γ-PMo ₉ O ₃₄ ] ^9- , or [α-SiMo ₉ O ₃₄ ] ^10- and/or [β-SiMo ₉ O ₃₄ ] ^10- and/or [γ-SiMo ₉ O ₃₄ ] ^10- , or [α-GeMo ₉ O ₃₄ ] ^10- and _/ or [β-GeMo ₉ O ₃₄ ] ^10- and/or [γ-GeMo ₉ O ₃₄ ] ^10-, where Q in general formula ₍₂₎ ^is P, Si, or Ge.
Preferred are [α-PMo ₉ O ₃₄ ] ⁹⁻ , [α-SiMo ₉ O ₃₄ ] ¹⁰⁻ or [α-GeMo ₉ O ₃₄ ] ¹⁰⁻ , and particularly preferred are [α-PMo ₉ O ₃₄ ] ⁹⁻ or [α-SiMo ₉ O ₃₄ ] ¹⁰⁻ , in which Q is phosphorus or silicon.

Furthermore, when the polynuclear metal compound of the present invention has one structural portion derived from a heteropolyoxometalate compound, the heteropolyoxometalate anion contained in the polynuclear metal compound is represented by the following general formula (3):
[QR _p Z ₉ O _q ] ^r- (3)
(In the formula, Q represents a heteroatom; Z, which may be the same or different, represents a polyatom selected from Mo, V, Nb, or Ta; R represents a metal atom different from the heteroatom and the polyatom; p, q, and r are positive numbers, and r is determined by the valences of Q, R, and Z).

Examples of the heteropolyoxometalate anion include [α-PV 4 Mo 9 O 41 ] 3- and/or [β-PV ₄ Mo ₉ O ₄₁ ] 3- and/or [γ-PV ₄ Mo ₉ O ₄₁ ] ^3- , or [α-SiV ₄ Mo ₉ O ₄₁ ] ^4- and/or [β-SiV ₄ Mo ₉ O ₄₁ ] ^4- and/or [γ-SiV ₄ Mo ₉ O ₄₁ ] ^{4- ,} or [α-GeV ₄ Mo _{9 O 41} ] ^{4- and} /or [β-GeV ₄ Mo _{9 O 41 ]} ^4- and/or [γ-GeV ₄ Mo ₉ O ₄₁ ] ^4- .

The polynuclear metal compound of the present invention may be in the form of a salt. As counter cations for forming the salt, those mentioned above as counter cations for forming the polyoxometalate compound (A) are preferred.

The polynuclear metal compound of the present invention can be used as a catalyst for organic reactions, such as various oxidation reactions and acid-base reactions. It is also expected to be used in various fields such as medicine and functional materials.

The method for producing polynuclear metal compounds of the present invention can produce novel polynuclear metal compounds that are expected to be used in various fields such as catalysts, medicines, and functional materials.

FIG. 1 is a schematic diagram showing an outline of the production method of the present invention. 2(a) shows a polyhedron diagram of the single crystal of the manganese hexanuclear structure synthesized in Example 1. FIG. 2(b) shows an anisotropic temperature factor diagram of the single crystal of the manganese hexanuclear structure synthesized in Example 1. 3(a) shows a polyhedron diagram of the single crystal of the vanadium tetranuclear structure synthesized in Example 2. FIG. 3(b) shows an anisotropic temperature factor diagram of the single crystal of the vanadium tetranuclear structure synthesized in Example 2. 4(a) shows the ³¹ P-NMR spectrum of the tetranuclear vanadium structure compound synthesized in Example 2. FIG. 4(b) shows the ⁵¹ V-NMR spectrum of the tetranuclear vanadium structure compound synthesized in Example 2. FIG. 5 shows the results of mass spectrometry of the vanadium tetranuclear structure compound synthesized in Example 2.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass." "TBA" is an abbreviation for tetra-n-butylammonium, "acac" is an abbreviation for acetylacetonate, and "py" is an abbreviation for pyridine.

For X-ray crystal structure analysis, diffraction data was acquired using a Rigaku MicroMax-007 Saturn724, and analysis was performed using a SHELXL-2014.
Mass spectrometry was performed using a JEOL JMS-T100CS.
³¹ P-NMR and ⁵¹ V-NMR measurements were performed using a JEOL JNM-ECA500, with a solution of H ₃ PO ₄ in D ₂ O and a solution of NaVO ₃ in D ₂ O as external standards.
IR measurements were carried out using a JASCO FT/IR-4100.

Example 1 Synthesis of Mn hexanuclear structure compound Compound I (TPP ₃ [A-α-PMo ₉ O ₃₁ (py) ₃ ], TPP salt TPP=tetraphenylphosphonium; 500 mg, 0.19 mmol) and manganese acetylacetonate Mn(acac) ₂ (143 mg, 0.57 mmol, 3 equivalents relative to compound I) were mixed in 1,2-dichloroethane (100 mL), and the solution was stirred at 50° C. for 2 hours. The reaction solution was filtered through a membrane filter, and then diethyl ether (5.0 mL) was added and the solution was allowed to stand at room temperature. After one day, a single crystal of a Mn hexanuclear structure compound suitable for single crystal X-ray structure analysis was obtained from the solution (104 mg, yield 21%).

The mass spectrometry (MS) measurement results of the obtained crystals are as follows.
Positive-ion MS (ESI, acetonitrile): found m/z = 3059.814 ₍ calculated m/z = 3059.837; _{[ TPP8} {Mn(acac)} _2Mn4 ( _PMo9O34 ) ₂ ] ²⁺ ).
The results of X-ray structural analysis of the obtained crystals are shown in Table 1.

Typical bond lengths and angles for single crystals of Mn hexanuclear structure compounds are shown in Table 2.

Example 2 Synthesis of V tetranuclear structure compound Vanadyl acetylacetonate (VO(acac) ₂ , 212 mg, 0.80 mmol) was dispersed in acetone (10 mL), and water (0.10 mL) and compound I (TBA ₃ [A-α-PMo ₉ O ₃₁ (py) ₃ ], TBA salt TBA=tetra-n-butylammonium; 488 mg, 0.20 mmol) were added to this solution. After stirring this solution at room temperature for one hour, the resulting precipitate was collected by filtration using a membrane filter. This precipitate was dissolved in a mixed solvent of dichloromethane and acetonitrile, and a 70% aqueous solution of nitric acid (26 μL, 0.40 mmol) was added, and the solution was vigorously stirred for 5 minutes. Then, diethyl ether (3 mL) was added and the mixture was allowed to stand to obtain a single crystal of V tetranuclear structure compound (160 mg, yield 32%).

The results of mass spectrometry (MS), ³¹ P-NMR and ⁵¹ V-NMR, IR and elemental analysis of the obtained crystals are as follows.
Positive-ion MS (CSI, acetonitrile): found m/z=2724.5 (calculated m/z=2724.2; [TBA ₄ PV ₄ Mo ₉ O ₄₁ ] ⁺ ).
³¹ P-NMR (202.47 MHz, acetonitrile-d ₃ ): δ=−3.75 ppm.
⁵¹ V-NMR (131.6 MHz, acetonitrile-d ₃ ): δ=−593.8, −587.8, −593.3 ppm (integral ratio 1:2:1).
IR (KBr pellet) 1635, 1483, 1384, 1152, 1073, 1048, 1007, 952, 877, 802, 650, 595, 511, 381, 373 cm ^-1 .
Elemental analysis: Calculated (%) _{for TBA3PV4Mo9O41} : P, 1.25; Mo, 34.79; _V , 8.21. Found: _P , 1.26; Mo, 38.21; V, 7.97.
The results of X-ray structural analysis of the obtained crystals are shown in Table 3.

From the above-mentioned examples, the synthesis of a novel Mn hexanuclear structure compound and a novel V tetranuclear structure compound was confirmed.
In the above-mentioned examples, a polyoxometalate compound having a structure in which a polyatom (Mo) is coordinated to a heteroatom (P) via an oxygen atom and pyridine is introduced at the defective structural site is reacted with manganese acetylacetonate or vanadyl acetylacetonate. However, if a polyoxometalate compound has a structure in which at least one polyatom selected from the group consisting of Mo, V, Nb, and Ta is coordinated to a heteroatom via an oxygen atom and an unshared electron pair-containing compound is introduced at the defective structural site, it is considered that the polyoxometalate compound having the specific polyatom described above is sufficiently stabilized by the introduction of the unshared electron pair-containing compound, and therefore it is certain that a wide variety of novel polynuclear metal compounds can be obtained by reacting this with a compound containing a metal atom different from the heteroatom and the polyatom.

Claims (4)

A method for producing a polynuclear metal compound having a structure in which a metal atom other than a hetero atom and a poly atom is introduced into a defective structural site of a polyoxometalate compound, comprising the steps of:
The production method includes a step of reacting a polyoxometalate compound (A) having a structure in which a polyatom, which is Mo, is coordinated to a heteroatom via an oxygen atom and an unshared electron pair-containing compound is introduced into a defective structural site with a compound (B) containing a metal atom different from the heteroatom and the polyatom ,
the atom having an unshared electron pair contained in the unshared electron pair-containing compound is at least one atom selected from the group consisting of a nitrogen atom, an oxygen atom, a phosphorus atom, and a sulfur atom;
The metal atom different from the heteroatom and the polyatom is at least one selected from the group consisting of a 3d transition metal atom, a 4d transition metal atom, a 5d transition metal atom, and a rare earth element.
2. A method for producing a polynuclear metal compound comprising the steps of: 2. The method for producing a polynuclear metal compound according to claim 1, wherein the heteroatom is at least one selected from the group consisting of Si, P, Al, S, Ge, As, and Se. The method for producing a polynuclear metal compound according to claim 1 or 2, characterized in that the compound (B) having a metal atom other than a heteroatom and a polyatom contains at least one group selected from the group consisting of a carboxylate group, a trifluoromethanesulfonate group, and an acetylacetonate group. A polynuclear metal compound having a structure in which a metal atom other than a hetero atom and a poly atom is introduced into a defective structural site of a polyoxometalate compound,
The polynuclear metal compound has a structure in which a polyatom, which is Mo, is coordinated to a heteroatom via an oxygen atom ,
The metal atom different from the heteroatom and the polyatom is at least one selected from the group consisting of a 3d transition metal atom, a 4d transition metal atom, a 5d transition metal atom, and a rare earth element.
A polynuclear metal compound comprising:

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