Tris(t-butyl)terpyridine-copper(ii) complexes and ligand field effects

A series of [Cu(L(3)')(NCS)(L/X)](+/0) complexes (L(3)' = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine; L = CH(3)OH; X = NCS, [NCAuCN]) has been prepared and characterized with X-ray crystallography, UV-vis and IR spectroscopies, and DFT calculations. The structure of starting material [Cu(L(3)')(NO(3))(2)], , was determined as well as the structures of the five-coordinate copper isothiocyanate complexes [Cu(L(3)')(NCS)(MeOH)](PF(6)), , [Cu(L(3)')(NCAuCN)(NCS)], , and two pseudo-polymorphs of bis-isothiocyanate [Cu(L(3)')(NCS)(2)], 3a and 3b.CH(3)CN. The square pyramidal structures of and differ markedly from the more trigonal bipyramidal [Cu(terpy)(NCS)(2)]. Electronic structure calculations suggest that the sigma-donor ability of the polyimine ligand controls the metal center geometry. The IR spectroscopic analysis shows that the nu(CN) stretching frequencies do not correlate predictably with structural parameters, such as the Cu-N-CS bond angle, demonstrating the oversimplification of the linear Cu-N[triple bond, length as m-dash]C-S vs. bent Cu-N=C=S modelling of isothiocyanate bonding.