Coordination of Zn(II), Cd(II), Hg(II), and Ag(I) by Bis(benzimidazole) Ligands

Abstract

The coordinating environments provided by the 1-(5,6-dimethylbenzimidazolyl)-3-benzimidazolyl-2-thiapropane (1), 1-(5,6-dimethylbenzimidazolyl)-3-benzimidazolyl-2-oxapropane (2), 1-(N-methyl)benzimidazolyl-3-benzimidazolyl-2-oxapropane (3), and 1,7-bis(benzimidazol-2-yl)-2,6-dithiaheptane (4) ligands for a series of soft-to-borderline metal ions have been demonstrated by crystallographic structure determination in the solid state, supplemented by multinuclear NMR studies in solution. Structures of [Zn(3)(H2O)(MeCN)](ClO4)2 ([C19H21N5O2Zn](ClO4)2, monoclinic, space group P21/c, a = 10.3247(11) Å, b = 11.0320(12) Å, c = 20.761(2) Å, β = 96.465(3)°, V = 2349.7(4) Å3, Z = 4), [Zn(1)Cl2]·CH3OH ([C18H18Cl2N4SZn]·CH4O, triclinic, space group P1̄, a = 9.0917(9) Å, b = 9.9186(10) Å, c = 12.2079(12) Å, α = 99.710(3)°, β = 94.252(2), γ = 95.598(3)°, V = 1075.3(2) Å3, Z = 2), [Hg(1)Br2]·CH3OH ([C18H18Br2HgN4S]·CH4O, triclinic, space group P1̄, a = 9.1956(12) Å, b = 9.9775(13) Å, c = 12.462(2) Å, α = 99.239(3), β = 97.676(3)°, γ = 94.036(3)°, V = 1113.4(3) Å3, Z = 2), [Cd(1)Cl2] ([C18H18CdCl2N4S], monoclinic, space group P21/n, a = 14.5219(11) Å, b = 8.5315(7) Å, c = 15.6182(12) Å, β = 92.063(2)°, V = 1933.7(3) Å3, Z = 4), and [Ag(4)](NO3) ([C19H20AgN4S](NO3), monoclinic, space group C2/c, a = 13.7339(3) Å, b = 17.2710(1) Å, c = 9.8866(2) Å, β = 115.399(1)°, V = 2118.4(1) Å3, Z = 4) have been determined. Ligand 3 provided the expected N2O donor set to Zn(II) forming part of a pseudo-trigonal bipyramidal coordinating environment, tentatively extrapolated to the Zn(II), Cd(II), and Hg(II) complexes of ligand 2 from 1H NMR studies. The thioether-bridged ligands (1 and 4) displayed a strikingly different coordination mode; in none of these structures was the thioether found to be coordinated to the central metal ion, resulting in pseudotetrahedral structures for the Zn(II) and Hg(II) complexes of ligand 1, a bis(chloro)-bridged dimeric five-coordinate complex of Cd(II) with ligand 1, and a near-linear coordination mode for the Ag(I) complex of ligand 4. No significant distinction in geometric parameters around the metal ions could be observed resulting from the introduction of asymmetry and a change of pK a within the bis(benzimidazole) ligands. Using 199Hg NMR spectroscopy, it was demonstrated that the thioether of ligand 1 did not coordinate in solutions of the 1:1 HgBr2 complex; negligible shifts of the signals corresponding to the aliphatic bridging protons in the 1H NMR spectra of ligand 1 when coordinated to Zn(II), Cd(II), and Hg(II) also suggested a noncoordinating behavior. Exchanges occurring in mixtures of HgBr2 and ligand 1 were examined using 199Hg, 13C, and 1H NMR. It is considered that there is little or no exchange occurring in a region of excess mercury on the 199Hg NMR time scale, and in a region of excess ligand 1 the 1/1 complex predominates.

2,5‐Diphenyl‐3,4‐bis(2‐pyridyl)cyclopenta‐2,4‐dien‐1‐one as a Redox‐Active Chelating Ligand

“…Essentially the same behaviour was observed by Lockhart et al for a bidentate bis(benzimidazole) ligand. [14] In their case, however, the dimeric cadmium complex is trigonal-bipyramidal with strongly asymmetric chloro bridges. The degree of covalency of the M À X bond increases in the order Zn < Cd < Hg and Cl < Br, reflecting relative valence orbital binding energies.…”

FT-Raman, FT-IR and NMR spectra, vibrational assignments and density functional studies of 1,3-bis(benzimidazol-2-yl)-2-thiapropane ligand and its Zn(II) halide complexes

“…Depending on donor or ligand types, distorted tetrahedral, square planar, five-coordinate geometries and octahedral are frequently observed geometries. The coordinating environment provided by the thioether-bridging ligand (L) and its several species with various transition metal ions, including Zn 2+ have been previously examined crystallographically [11,12]. In the solid state, thioether ligand provided the expected N 2 donor set from the tertiary imine nitrogen atoms forming preferred four-co-ordinate tetrahedral environment, and the remaining coordination sites were filled by halide anions [12].…”

“…The coordinating environment provided by the thioether-bridging ligand (L) and its several species with various transition metal ions, including Zn 2+ have been previously examined crystallographically [11,12]. In the solid state, thioether ligand provided the expected N 2 donor set from the tertiary imine nitrogen atoms forming preferred four-co-ordinate tetrahedral environment, and the remaining coordination sites were filled by halide anions [12]. Metal ion selectivity and transportation ability of several bis(benzimidazloe) ligands have also been studied in terms of the condition (pH), bridge length, donating atom (hard-soft principle) and the geometrical constrains provided by the ligands [13] Although the spectroscopic studies, particularly on the vibrational frequencies of the bis-benzimidazole derivatives and some metal(II) halide complexes have been previously reported.…”

Synthesis of Zn compounds derived from 1H-benzimidazol-2-ylmethanamine

“…4,[6][7][8] The interaction of Zn(II) ion with the environment of the Polyligand derived from imidazole and benzimidazole are used as working models to understanding the role of the Zn(II) ions in biological systems because they can mimic the histidine side chain. 4,[7][8][9] In our ongoing research on benzimidazole derivatives we are interested in the coordinating acid and behavior of 1H-benzimidazol-2-ylmethanamine (HL) 1.…”