EPR spectroscopy of 4,4'-bis(tert-butyl)-2, 2'-bipyridine-1, 2-dithiolatocuprates(II) in host lattices with different coordination geometries

摘要

A series of new heteroleptic MN _2S _2 transition metal complexes with M = Cu ~(2+) for EPR measurements and as diamagnetic hosts Ni ~(2+), Zn ~(2+), and Pd ~(2+) were synthesized and characterized. The ligands are N _2 = 4, 4'-bis(tert-butyl)-2, 2'-bipyridine (tBu _2bpy) and S _2 =1, 2-dithiooxalate, (dto), 1, 2-dithiosquarate, (dtsq), maleonitrile-1, 2-dithiolate, or 1, 2-dicyanoethene-1, 2-dithiolate, (mnt). The Cu ~(II) complexes were studied by EPR in solution and as powders, diamagnetically diluted in the isostructural planar [Ni ~(II)(tBu _2bpy)(S _2)] or[Pd ~(II)(tBu _2bpy)(S _2)] as well as in tetrahedrally coordinated[Zn ~(II)(tBu _2bpy)(S _2)] host structures to put steric stress on the coordination geometry of the central CuN _2S _2 unit. The spin density contributions for different geometries calculated from experimental parameters are compared with the electronic situation in the frontier orbital, namely in the semi-occupied molecular orbital (SOMO) of the copper complex, derived from quantum chemical calculations on different levels (EHT and DFT). One of the hosts, [Ni ~(II)(tBu _2bpy)(mnt)], is characterized by X-ray structure analysis to prove the coordination geometry. The complex crystallizes in a square-planar coordination mode in the monoclinic space group P2 _1/a with Z = 4 and the unit cell parameters a = 10.4508(10) ?, b = 18.266(2) ?, c = 12.6566(12) ?, β = 112.095(7)°. Oxidation and reductions potentials of one of the host complexes, [Ni(tBu 2bpy)(mnt)], were obtained by cyclovoltammetric measurements.