Development ofa new class of complexes of pyrazolates

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Polynuclear transition metal complexes with pyrazoles and/or pyrazolates have been attracting much attention because of their versatile structures and properties. By using the bridging ability of pyrazolates, it is possible to construct cyclic polynuclear complexes. Although tetranuclear, hexanuclear, or octanuclear cyclic complexes are also known, the most popular cyclic complex is the trinuclear one, in which monovalent two-coordinate metal ions are singly bridged by pyrazolates to form [M^I_3(μ-Rpz)_3](M=Ag,An,Cu,Co;Rpz=pyrazolate or substituted pyrazolates). We have been thinking the possibility that pyrazolates can form cyclic trinuclear complexes with various transition metals such as acetates, and thus we have conducted this project.In this project, we have succeeded to synthesize the cyclic trinuclear palladium(II) complex [Pd3(μ-pz)_6], which has very similar structure to [Pd_3(μ-pz)_6]. It prompted us to make metal-metal bonding by using [Pt_3(μ-pz)_3], because [Pd_3(μ-pz)_6] is hard to oxidize due to smaller distribution of 4d orbital. Actually, we have succeeded to oxidize [Pt_3(μ-pz)_6]. The partially oxidized Pt(II,III,III)_3 species [Pt_3Br_2(μ-pz)_6] has intense blue color, which was attributed to the dσ→dσ^* transition (HOMO-LUMO transition).