Synthesis, characterization and structure of transition metal complexes of 4′-methylthio-2,2′:6′,2″-terpyridyl

Reaction of 2 equiv. of an ethanolic solution of 4′-methylthio-2,2′:6′,2″-terpyridyl (4′-MeSterpy) with M(ClO4)2 [M=Mn, Fe, Co, Ni, Cu, Zn] yields stable complexes of the form [M(4′-MeSterpy)2](ClO4)2·nH2O. Single crystal X-ray diffraction studies of the manganese, iron and nickel complexes show a distorted octahedral geometry around each metal center with the two ligands meridinally aligned. The iron and nickel complexes occur as triclinic crystals in the space group P1̄ while the manganese complex is monoclinic in the space group P21/c. The NMR spectra for the diamagnetic iron and zinc complexes show strong upfield shifts for two of the aromatic resonances. The mono-4′-MeSterpy complexes, Zn(4′-MeSterpy)Cl2 and Zn(4′-MeSterpy)(NO3)2 were also prepared and their structures determined for comparison with the bis complexes. The chloride complex crystallizes in P1̄ while the nitrate complex is in the space group, C2/c. Strong upfield shifts of the ligand resonances are not observed in the NMR spectra of these complexes leading to the conclusion that the upfield shifts arise from through space shielding effects between the ligands in the bis(4′-MeSterpy) compounds.