Mercury (II) coordination complexes bearing Schiff base ligands: What affects their nuclearity and/or dimensionality

A series of seven new mercury (II) Schiff base compounds were synthesized and characterized using single-crystal X-ray crystallography and other spectroscopic and physical methods. The complexes feature the ligands L1 and L2 [L1 = (N,N-bis(pyridine-2-yl)benzylidene)-2,2′-dimethylpropane-1,3-diamine; L2 = (N,N-bis(pyridine-2-yl)benzylidene)butane-1,4-diamine], and are either dinuclear, namely complex [Hg(L1)(μ-Cl)HgCl3] (1), mononuclear, namely [Hg(L1)Br2] (2), [Hg(L1)I2] (3), [Hg(L1)(SCN)2] (4), polynuclear polymeric, namely [Hg8(μ-L2)2(μ-Cl)6(μ3-Cl)4Cl4]n (5), [Hg2(L2)Br4]n (6) or molecular dimeric, namely [Hg2(L2)I4] (7). The syntheses of these complexes were achieved using mild solvothermal conditions, in a locally-developed apparatus. The microanalyses and spectroscopic results corroborate the structural data from single crystal X-ray diffraction; the latter proved the versatility of Hg(II) coordination chemistry, since simple variation of the Schiff base chelate or the halide/pseudohalide counterion resulted in distinctively different complexes. In the dinuclear compound 1, the asymmetric unit contains two different mercury(II) centers with tetrahedral and square pyramidal geometries, whereas in 2–4 the metal ion adopts a distorted octahedral geometry. The coordination polymers 5 and 6 have 3D and 1D structures, respectively, in which each mercury(II) center is five-coordinate with a square pyramidal geometry, whereas both Hg(II) centers in 7 are tetrahedral.

This work describes the syntheses and characterization of seven new HgII coordination complexes, with various metal coordination geometries, cluster nuclearities, as well as aggregate architectures. This serves as an investigation of the Schiff base ligands in HgII coordination chemistry, and is proof of the inherent versatility of HgII and the ligand systems considered.Figure optionsDownload as PowerPoint slide