Studies involving mixed donor macrocyclic ligands. Comparative X-ray diffraction, infrared, and fast atom bombardment mass spectrometric studies of the nickel thiocyanate complexes of three O2N3-donor macrocycles

Abstract

Minor changes in the substitution pattern of the backbone of a 17-membered macrocyclic ring incorporating O₂N₃ donor atoms have been demonstrated to have a significant influence on the ligand co-ordination modes in the corresponding nickel thiocyanate complexes. Comparative i.r. and fast atom bombardment (f.a.b.) source mass spectrometry as well as X-ray diffraction studies (on three complexes) have been used to elucidate the nature of the species formed. A variety of structures occurs for these complexes: three of the complexes are monomeric and incorporate terminal isothiocyanato groups with the 1,4,7-triazaheptane macrocyclic fragment co-ordinating in either a facial or meridional manner. Two forms of the complex of the unsubstituted macrocycle were isolated. The more insoluble form is dimeric and incorporates unusual N-bridged isothiocyanato groups. The combination of i.r. and f.a.b. mass spectrometric studies has proven to be especially useful for structural elucidation in systems of the type investigated.