No abstract

Treatment of the bmnpa (N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine) ligand with equimolar amounts of Cd(ClO(4))(2).5H(2)O and Me(4)NOH.5H(2)O in CH(3)CN yielded the binuclear cadmium hydroxide complex [((bmnpa)Cd)(2)(mu-OH)(2)](ClO(4))(2).CH(3)CN (1). Complex 1 may also be prepared (a) by treatment of a CH(3)CN solution of (bmnpa)Cd(ClO(4))(2) (2) with 1 equiv of n-BuLi, followed by treatment with water or (b) from 2 in the presence of 1 equiv each of water and NEt(3). The hydroxide derivative 1 is not produced from 2 and water in the absence of an added base. Complex 1 possesses a binuclear structure in the solid state with hydrogen-bonding and CH/pi interactions involving the bmnpa ligand. The overall structural features of 1 differ from the halide derivative [((bmnpa)Cd)(2)(mu-Cl)(2)](ClO(4))(2) (3), particularly in that the Cd(2)(mu-OH)(2) core of 1 is symmetric whereas the Cd(2)(mu-Cl)(2) core of 3 is asymmetric. In acetonitrile solution, 1 behaves as a 1:2 electrolyte and retains a binuclear structure and secondary hydrogen-bonding and CH/pi interactions, whereas 3 is a 1:1 electrolyte, indicating formation of a mononuclear [(bmnpa)CdCl]ClO(4) species in solution. Treatment of 1 with CO(2) in anhydrous CH(3)CN yields the bridging carbonate complex [((bmnpa)Cd)(2)(mu-CO(3))](ClO(4))(2).CH(3)CN (4). Treatment of a chemically similar zinc hydroxide complex, [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2) (benpa = N,N-bis-2-(ethylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine, with CO(2) also results in the formation of a carbonate derivative, [((benpa)Zn)(2)(mu-CO(3))](ClO(4))(2) (5), albeit the coordination mode of the bridging carbonate moiety is different. Treatment of 4 with added water results in no reaction, whereas 5 under identical conditions will undergo reaction to yield the zinc hydroxide complex [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2).

Treatment of a dinuclear zinc hydroxide complex ([(bmnpaZn)2(μ-OH)2](ClO4)2 (1) or [(benpaZn)2(μ-OH)2](ClO4)2 (2)) with excess equivalents of an aryl alcohol derivative (p-HOC6H4X; X = NO2, CHO, CN, COCH3, Br, H, OCH3) yielded the nitrogen/sulfur-ligated zinc aryloxide complexes [(bmnpa)Zn(p-OC6H4NO2)](ClO4) (3), [(benpa)Zn(p-OC6H4NO2)](ClO4) (4), [(benpa)Zn(p-OC6H4CHO)](ClO4) (5), [(benpa)Zn(p-OC6H4CN)](ClO4) (6), [(benpa)Zn(p-OC6H4COCH3)](ClO4)·0.5H2O (7), [(benpa)Zn(p-OC6H4Br)](ClO4) (8), [(benpa)Zn(p-OC6H5)](ClO4) (9), and [(benpa)Zn(p-OC6H5OCH3)](ClO4) (10). The solid state structures of 2, 3, 5, and 6 have been determined by X-ray crystallography. While 3 and 6 exhibit a mononuclear zinc ion possessing a distorted five-coordinate trigonal bipyramidal geometry, in 5 each zinc center exhibits a distorted six-coordinate octahedral geometry resulting from coordination of the aldehyde carbonyl oxygen of another zinc-bound aryloxide ligand, yielding a chain-type structure. Zinc coordination of the aldehyde carbonyl of 5 is indicated by a large shift (>40 cm-1) to lower energy of the carbonyl stretching vibration (νC  O) in solid state FTIR spectra of the complex. In the solid state structures of 3, 5, and 6, a hydrogen-bonding interaction is found between N(3)−H of the supporting bmnpa/benpa ligand and the zinc-bound oxygen atom of the aryloxide ligand (N(3)···O(1) ∼ 2.78 Å). Solution 1H and 13C NMR spectra of 3−10 in CD3CN and FTIR spectra in CH3CN are consistent with all of the aryloxide complexes having a similar solution structure, with retention of the hydrogen-bonding interaction involving N(3)−H and the oxygen atom of the zinc-coordinated aryloxide ligand. For this family of zinc aryloxide complexes, a correlation was discovered between the chemical shift position of the N(3)−H proton resonance and the pK a of the parent aryl alcohol. This correlation indicates that the strength of the hydrogen-bonding interaction involving the zinc-bound aryloxide oxygen is increasing as the aryloxide moiety increases in basicity.