Mercury(II) cyanide complexes with alkyldiamines: Solid-state/solution NMR, computational, and antimicrobial studies

Mercury cyanide complexes of alkyldiamines (1-6), [Hg(L)(CN) ₂] (where L = en (1,2-diaminoethane), pn (1,3-diaminopropane), N-Me-en, N, N'-Me ₂-en, N, N'-Et ₂-en, and N, N'-ipr ₂-en), have been synthesized and characterized by elemental analysis, IR, ¹³C, and ¹⁵N solution NMR in DMSO-d ₆, as well as ¹³C, ¹⁵N, and ¹⁹⁹Hg solid-state NMR spectroscopy. Complexes 1 and 2 have been studied computationally, built and optimized by GAUSSIAN03 using DFT at B3LYP level with LanL2DZ basis set. Binding modes of en and bn (where bn = 1,4-diaminobutane) toward Hg(CN) ₂ are completely different. Complexes with en and pn show chelating binding to Hg(II), while bn behaves as a bridging ligand to form a polymeric structure, [Hg(CN) ₂-bn] _∞ [B.A. Al-Maythalony, M. Fettouhi, M.I.M. Wazeer, A.A. Isab. Inorg. Chem. Commun., 12, 540 (2009).]. The solution ¹³C NMR of the complexes demonstrates a slight shift of the -C≡N (0.9 to 2ppm) and -C-NH ₂ (0.25 to 6ppm) carbon resonances, while the other resonances are relatively unaffected. ¹⁵N labeling studies have shown involvement of alkyldiamine ligands in coordination to the metal. The principal components of the ¹³C, ¹⁵N, and ¹⁹⁹Hg shielding tensors have been determined from solid-state NMR data. Antimicrobial activity studies show that the complexes exhibit higher antibacterial activities toward various microorganisms than Hg(CN) ₂.