Steric Effects of Alkyl Substituents at N-Donor Bidentate Amines Direct the Nuclearity, Bonding and Bridging Modes in Isothiocyanato-Copper(II) Coordination Compounds

A series of Cu(II)-isothiocyanato coordination compounds derived from sterically hindered N-donor diamines were synthesized and characterized: catena-[Cu(Me(3)en)(-NCS)(NCS)] (1), catena-[Cu(NEt(2)Meen)(-NCS)(NCS)] (2), catena-[Cu(N,N,2,2-Me(4)pn)(-NCS)(NCS)] (3), the dimeric: [Cu-2(N,N-isp(2)en)(2)(mu-NCS)(2)(NCS)(2)] (4) and the monomeric compound [Cu(N,N-t-Bu(2)en)(NCS)(2)] (5), where Me(3)en = N,N,N-trimethylethylenediamine, NEt(2)Meen = N,N-diethyl-N-methylethylenediamine, N,N,2,2-Me(4)pn = N,N,2,2-tetramethylpropylenediamine, N,N-isp(2)en = N,N-diisopropylethylenediamine and N,N-t-Bu(2)en = N,N-di(tert-butyl)ethylenediamine. The coordination compounds were characterized by elemental microanalyses, IR, and UV-Vis spectroscopy as well as single crystal X-ray crystallography. Density Functional Theory (DFT) was used to evaluate the role of steric effects in compounds 4 and 5 and how this may affect the adaption of a specific geometry, NCS-bonding mode, and the dimensionality of the resulting coordination compound.