New supramolecular synthons based on 3d transition metal complexes with bidentate bispidines: Synthesis and structural, spectroscopic, and electrochemical studies

A new supramolecular synthon, a 2L: 1M complex of bidentate bispidine with transition metal, was suggested. A number of complex compounds of 1,5-dimethylbispidin-9-one with Cuii, Niii, and Coii salts (perchlorates, chlorides, bromides, nitrates, trifluoroacetates) were synthesized. The structure and composition of complexes obtained were estimated based on the combination of physicochemical methods of analysis (elemental analysis, X-ray diffraction analysis, NMR, IR, and Raman spectroscopy, electron absorption spectroscopy, ESI mass spectrometry, CVA). The composition of most complexes in the solid state corresponds to the formula ML2X2, and in a number of cases the fragment [ML2]2+ is retained in solution, which was shown by NMR spectroscopy for nickel complexes and by mass spectrometry for copper complexes. In the case of copper chloride, the composition of the acetonitrile solutions in the presence of the ligand depends on the ratio of starting compounds and their concentration: an increase in proportion of CuCl2 and concentration shifts the equilibrium to the side of complexes with higher nuclearity. A 2L: 1M complex of bispidine with metal was for the first time structurally characterized using copper(ii) nitrate derivative as an example. The CVA method showed existence of reversible electrochemical reduction of the metal for a number of complexes (the products of the reaction of 1,5-dimethylbispidin-9-one with nickel(ii) and cobalt(ii) chlorides, as well as with nickel(ii) bromide). According to the IR and Raman spectra, chelation of metals with 1,5-dimethylbispidin-9-one leads to the shift of the absorption band of the ligand carbonyl group from 1700 to 1721–1744 cm−1. Nickel(ii) and copper(ii) perchlorates and nitrates were concluded to be the most promising complexation agents for the binding of two NH,NH-bispidine ligands in a coordination polymer.