Development ofa new class of complexes of pyrazolates

多核过渡金属吡唑和/或吡唑酸盐配合物因其结构和性质的多样性而引起了人们的广泛关注。通过利用吡唑类化合物的桥联能力，可以构建环状多核配合物。虽然四核、六核或八核环状络合物也是已知的，但最常用的环状络合物是三核环状络合物，其中一价两配位的金属离子通过吡唑酸盐单桥接形成[M^I_3(μ-rpz)_3](M=Ag，An，Cu，Co；rpz=吡唑酸盐或取代吡唑酸盐)。我们一直在思考吡唑类化合物与各种过渡金属如乙酸酯形成环状三核配合物的可能性，因此我们进行了这一项目的研究，在这个项目中，我们成功地合成了与[Pd_3(μ-PZ)_6]结构非常相似的环状三核钯(II)配合物[Pd3(μ-PZ)_6]。这促使我们使用[Pt3(μ-PZ)3]进行金属-金属键合，因为[Pd_3(μ-PZ)_6]由于4d轨道分布较小而不易被氧化。实际上，我们已经成功地氧化了[Pt3(μ-PZ)6]。部分氧化的铂(II，III，III)3物种[Pt3Br2(μ-PZ)6]呈深蓝色，这是由于dσ→dσ^*转变(HOMO-LUMO转变)所致。

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).