Reactions of cadmium(ii) nitrate with 4-(trimethylammonio)benzenethiolate in the presence of N-donor ligands

Abstract

Reactions of Cd(NO₃)₂·4H₂O with TabHPF₆ (TabH = 4-(trimethylammonio)benzenethiol) and Et₃N in the presence of NH₄SCN and five other N-donor ligands such as 2,2′-bipyridine (2,2′-bipy), phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (2,9-dmphen), 2,6-bis(pyrazd-3-yl)pyridine (bppy) and 2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (bdmppy) gave rise to a family of Cd(II)/thiolate complexes of N-donor ligands, {[Cd₂(μ-Tab)₄(NCS)₂](NO₃)₂·MeOH}_n (1), [Cd₂(μ-Tab)₂(L)₄](PF₆)₄ (2: L = 2,2′-bipy; 3: L = phen), [Cd(Tab)₂(L)](PF₆)₂ (4: L = 2,9-dmphen; 5: L = bppy), and [Cd₂(μ-Tab)₂(Tab)₂(bdmppy)]₂(PF₆)₈·H₂O (6·H₂O). These compounds were characterized by elemental analysis, IR spectra, UV-Vis spectra, ¹H NMR, electrospray ionization (ESI) mass spectra and single-crystal X-ray diffraction. For 1, each [Cd(NCS)]⁺ fragment is connected to its equivalents via a pair of Tab bridges to a one-dimensional chain. For 2 and 3, two [Cd(2,2′-bipy)₂]²⁺ or [Cd(phen)₂]²⁺ units are linked by a pair of Tab bridges to form a cationic dimeric structure. The Cd atom in [Cd(Tab)₂(L)]²⁺ dication of 4 or 5 is coordinated by two Tab ligands and chelated by two N atoms from 2,9-dmphen (4) or three N atoms from bppy (5), forming a distorted tetrahedral (4) or trigonal bipyramidal (5) coordination geometry. For 6, each of two [Cd(Tab)(bdmppy)] fragments is linked to one [(Tab)Cd(μ-Tab)₂Cd(Tab)] fragment via two Tab bridges to generate a unique cationic zigzag tetrameric structure where the Cd centers take a tetrahedral or a trigonal bipyramidal coordination geometry. The results may provide an interesting insight into mimicking the coordination spheres of the Cd(II) sites of metallothioneins and their interactions with various N-donor ligands encountered in nature.