Synthetic Control of Pt···Pt Separation and Photophysics of Binuclear Platinum Complexes

A new series of luminescent μ-pyrazolate-bridged cyclometalated platinum binuclear complexes having the formula C∧NPt(μ-pz‘)2PtC∧N (C∧N = 2-(2,4-difluorophenyl)pyridyl, pz‘ = pyrazolate for 1, 3,5-dimethylpyrazolate for 2, 3-methyl-5-tert-butylpyrazolate for 3, and 3,5-bis(tert-butyl)pyrazolate for 4) have been synthesized and characterized. The two Pt(C∧N) moieties are bridged by two μ-pyrazolate ligands in an exo-bidentate fashion. A mononuclear complex with an isolated Pt center, C∧NPt(pz)2BEt2, 5, is also described. The X-ray crystal structures of 1−4 show the following Pt−Pt spacings: 1 = 3.3763(7) Å, 2 = 3.1914(9) Å, 3 = 3.0457(7) Å, and 4 = 2.8343(6) Å. At 77 K, the emission energy of the complexes varies from blue (for 1, 2, and 5) to green (for 3) to red (for 4). The changes in the photophysical properties of the binuclear complexes can be correlated with the decreasing Pt−Pt distance; the emissive state changes from a mixed ligand center triplet/metal-to-ligand charge transfer excited state (for 1 and 2) to a lower-energy, Pt−Pt metal−metal-to-ligand charge transfer state (for 3 and 4).本研究合成并表征了一系列通式为C∧NPt(μ-pz‘)₂PtC∧N的发光μ-吡唑酸根桥联环金属化铂双核配合物，其中C∧N配体为2-(2,4-二氟苯基)吡啶基，pz'在配合物1中为吡唑酸根，配合物2中为3,5-二甲基吡唑酸根，配合物3中为3-甲基-5-叔丁基吡唑酸根，配合物4中为3,5-双(叔丁基)吡唑酸根。两个Pt(C∧N)结构单元通过两个μ-吡唑酸根配体以外双齿配位模式桥联。本文同时报道了一种具有孤立铂中心的单核配合物5，其化学式为C∧NPt(pz)₂BEt₂。配合物1至4的X射线晶体结构测得其Pt-Pt间距分别为：1为3.3763(7) Å，2为3.1914(9) Å，3为3.0457(7) Å，4为2.8343(6) Å。在77 K条件下，各配合物的发射能量范围从蓝色（配合物1、2和5）到绿色（配合物3）再到红色（配合物4）。双核配合物的光物理性质变化可与Pt-Pt间距的递减相关联：其发射激发态从混合配体中心三重态/金属到配体电荷转移激发态（配合物1和2）转变为低能态Pt-Pt金属-金属到配体电荷转移激发态（配合物3和4）。