Solid-State and Solution-State Coordination Chemistry of the Zinc Triad with the Mixed N,S Donor Ligand Bis(2-methylpyridyl) Sulfide

Abstract

The binding of group 12 metal ions to bis(2-methylpyridyl) sulfide (1) was investigated by X-ray crystallography and NMR. Seven structures of the chloride and perchlorate salts of Hg(II), Cd(II), and Zn(II) with 1 are reported. Hg(1)(2)(ClO(4))(2), Cd(1)(2)(ClO(4))(2), and Zn(1)(2)(ClO(4))(2).CH(3)CN form mononuclear, six-coordinate species in the solid state with 1 binding in a tridentate coordination mode. Hg(1)(2)(ClO(4))(2) has a distorted trigonal prismatic coordination geometry while Cd(1)(2)(ClO(4))(2) and Zn(1)(2)(ClO(4))(2).CH(3)CN have distorted octahedral geometries. With chloride anions, the 1:1 metal to ligand complexes Hg(1)Cl(2), [Cd(1)Cl(2)](2), and Zn(1)Cl(2) are formed. A bidentate binding mode that lacks thioether coordination is observed for 1 in the four-coordinate, distorted tetrahedral complexes Zn(1)Cl(2) and Hg(1)Cl(2). [Cd(1)Cl(2)](2) is dimeric with a distorted octahedral coordination geometry and a tridentate 1. Hg(1)Cl(2) is comprised of pairs of loosely associated monomers and Zn(1)Cl(2) is monomeric. In addition, Hg(2)(1)Cl(4) is formed with alternating chloride and thioether bridges. The distorted square pyramidal Hg(II) centers result in a supramolecular zigzagging chain in the solid state. The solution (1)H NMR spectra of [Hg(1)(2)](2+) and [Hg(1)(NCCH(3))(x)()](2+) reveal (3)(-)(5)J((199)Hg(1)H) due to slow ligand exchange found in these thioether complexes. Implications for use of Hg(II) as a metallobioprobe are discussed.

Synthesis, Stability Constant Determination, and Structural Study of Some Complexes of a Zinc Triad Containing Pyridyl‐amine‐quinoline and Pyridyl‐thio‐quinoline

“…[38] (2.685 Å). A similar situation with shorter and longer Hg-N distances has been reported by Bebout [14] [2.382(4), 2.409(4) Å, 2.501(4), 2.511(4) Å] as well as in the cation described in ref. [39] (2.351, 2.418, 2.413 Å).…”

“…Search (a) returned ten entries, in which the Hg II -S(thioether) distance varies between 2.458 [34] and 3.050 [34] Å. In 2, there is a shorter and a longer Hg-S bond [2.621(4) Å and 2.749(5) Å], a situation already found by Bebout [14] [bonds of 2.654(1) and 2.671(1) Å] and also quite similar to what was observed in the complexes described in ref. [35] (bonds of 2.654, 2.735, 2.639, 2.751 Å) and ref.…”

“…The lack of any observable coupling constants could be traced back to the small value of the constant itself or to the rapid exchange of the ligand among complexes. The authors, however, on the basis of their own experience with these kinds of ligands and according to previous observations, [14] are inclined to believe that the ligands in these cases are not firmly bound to the central metal and that a fluxional rearrangement affects these complexes in solution. As a matter of fact, the solid-state structure of the complex [Hg(NSN) 2 (OClO 3 )]ClO 4 was clearly produced by the displacement of one terminus of the potentially terdentate ligand (the quinoline nitrogen) by the oxygen of a perchlorate ion.…”

“…[27] It is worth noting that complexes in which a five-coordinate Hg II is surrounded at the same time by pyridyl and thioether ligands are rather uncommon. [22,25] Recently, Bebout and co-workers [14] described some zinc triad complexes (with c.n. = 4, 5, or 6) of a symmetric N,S mixed ligand (L) closely related to NSN(Qui [14] Search (c) returned about 20 entries, but only 11 of these show an aliphatic amine donor atom like 3.…”

“…[22,25] Recently, Bebout and co-workers [14] described some zinc triad complexes (with c.n. = 4, 5, or 6) of a symmetric N,S mixed ligand (L) closely related to NSN(Qui [14] Search (c) returned about 20 entries, but only 11 of these show an aliphatic amine donor atom like 3. In the reported structures, the Zn-N py , Zn-N ali (N py = pyridine nitrogen, N ali = aliphatic amine nitrogen), and Zn-Cl distances vary, respectively, in the ranges 2.039 [28] -2.511, [28] 2.129 [29] -2.464, [30] and 2.220 [30] -2.345 [29] Å.…”