Group 12 coordination complexes of a tridentate imidazolyl ligand

Histidine is an essential amino acid with crucial involvement in antioxidant activity, metal-ion chelation, and toxic metal scavenging, and has demonstrated utility in Zn(II) coordination of many fundamental human proteins, like carbonic anhydrases. This prevalence of histidine in Zn(II) metalloprotein coordination sites has prompted group 12 coordination studies of a similar imidazole bis[2-(1-methylimidazolyl)methyl] amine ligand, nicknamed BMIMA. Here, we present the synthesis, characterization, crystallographic data, and crystal analysis of a suite of five- and six-coordinate divalent group 12 metal ions in complex with BMIMA in 1:1 and 1:2 metal ligand ratios. The compounds are characterized using X-ray crystallography, 1H NMR, IR, and elemental analysis. Bond angles around the central metal atom have elucidated a preferred square pyramidal orientation with heavier group 12 [M(BMIMA)Cl2] compounds and a particular trend of cis-facial geometry maintained by the [M(BMIMA)2](ClO4)2 complexes. Offset face-to-face (OFF) and edge-to-face (EF) intermolecular aromatic interactions are visualized for the complexes, providing synthetic parallels to crucial interactions stabilizing biomacromolecules. Furthermore, Hirshfeld surfaces generated for select complexes qualitatively detail relevant close contacts and possible hydrogen donor and acceptor roles, and deconstructed 2D fingerprint plots and various surface properties applied to the Hirshfeld surface glean additional information on these intermolecular contacts. A highly unusual triangular, non-bridging Hg34+ complex is also presented due to its inadvertent synthesis during crystallization trials of [Hg(BMIMA)Cl2]. Its distinct structure was found to be novel and lacking comparable analogs, facilitating discussion on its unique molecular geometry.