Pseudotetrahedral Co II complexes with thio- and seleno-carbamate esters

Abstract

Thiocarbamate esters L = RHNCSOR′ act as unidentate ligands through their S atoms towards Co II giving pseudotetrahedral CoL 2X 2 (X = Cl, Br, I) complexes. The complexing behaviour of L is therefore similar to that of substituted thioureas RHNCSNHR′, also in electronic spectral patterns and spectrochemical parameters values. However, the effect of -OR′ substituents compared to -NHR′ of thioureas reduces markedly the affinity of thiocarbonyl sulfur for Co II, and results in much more limited stability and easier solvolytic displacement of thiocarbamate complexes. Selenocarbamate complexes appear to be even less stable than the corresponding thiocarbamate complexes, but nevertheless CoL′X 2 (L′= N-phenyl-O-methylselenocarbamate, X = Br, I) could be prepared; their electronic spectra are consistent with lower spectrochemical position and stronger nephelauxetic effect of the Se donors. The crystal and molecular structure of one of these complexes, dibromo-bis(O-ethyl,N-phenylthiocarbamate)cobalt(II), Co[(C 6H 5)NHCS(OC 2H 5)] 2Br 2, has been determined from three-dimensional single-crystal X-ray data collected by standard film techniques. The structure has been refined by least-squares methods to a conventional R factor of 0.078 for 1330 non zero reflections. The neutral complex crystallises in space group C2/c of the monoclinic system with a cell of dimensions a = 25.95±0.02, b = 5.82±0.02, c= 15.22±0.02 Å, β = 104.3±1°; V = 2227 Å 3. ϱ(exp) is 1.72±0.04 g/cm 3 in good agreement with 1.73 g/cm 3 as calculated for Z = 4. The molecule is crystallographically required to possess a twofold symmetry axis with cobalt occupying the 4(e) special positions of the space group. The complex consists of a cobalt atom tetrahedrally coordinated by two bromine atoms and by sulphur atoms of the two thiocarbamate ligands. The CoBr and CoS distances are 2.394(2) and 2.238(3) Å respectively. A strong hydrogen bond interaction between the hydrogen belonging to nitrogen and the bromine has been revealed (HN ... Br = 3.36 Å). Several features of the geometry within the molecule are also given and discussed.