Structures and Spectroscopic Properties of Chain Polymeric Complexes of Copper(II) Halides with 2,3,5,6-Tetrafluoro-1,4-bis(2-pyridylsulfenyl)benzene and Its 4-Pyridylsulfenyl Analogue

The syntheses are reported of the “extended reach” ligand 2,3,5,6-tetrafluoro-1,4-bis(2-pyridylsulfenyl)benzene
(L1), its 4-pyridylsulfenyl analogue (L2), and their copper(II) complexes CuLX2 (X = Cl or Br). X-ray studies
have been carried out on L1, L2, and the complexes Cu(L1)Cl2·2CHCl3 (1) and [Cu(L2)(DMF)Br2]·DMF (2).
Complex 1 has a chain polymeric structure with a trans-planar CuCl2N2 coordination geometry. Complex 2 is
also a chain polymer structure, but in this case a DMF molecule is bonded in the apical position above a trans-CuBr2N2 unit, producing a slightly distorted square pyramidal geometry at the copper centers. The transition
energies obtained from the single-crystal electronic spectrum of Cu(L1)Cl2·2CHCl3 and the g-values from its
EPR spectrum are used to derive bonding parameters, and these are compared with those of other planar CuL2Cl2
complexes with amine ligands. The electronic reflectance spectrum of [Cu(L2)(DMF)Br2]·DMF implies broadly
similar amine bonding parameters. This compound exhibits an unusual g-tensor with g|| < g⊥, which is interpreted
in terms of exchange-averaging of the molecular g-tensors of the two molecules in the unit cell.