Synthesis and structures of soluble magnesium and zinc carboxylates containing intramolecular NH center dot center dot center dot O hydrogen bonds in nonpolar solvents

摘要

Readily soluble magnesium and zinc carboxylates [M(Ln)(2)(H2O)(4)] (MLn(2)) (M = Mg, Zn; L1 = O2C-2-Ar3CCONH-6-n-BuCONHC6H3; L2 = O2C-2-Ar3CCONHC6H4; Ar = 4-t-BuC6H4) containing intramolecular NH center dot center dot center dot O hydrogen bonds in nonpolar solvents were synthesized and their molecular structures were determined by X-ray analysis. The complexes were crystallized in the trans or cis configuration. The M-O bond distances were dependent on the mode of the hydrogen bonds. H-1 NMR spectral measurements revealed a fast trans-cis isomerization of MLn(2) in CDCl3, which was converted into a unique fac[M(Ln)(3)(H2O)(3)](-) (fac-[MLn(3)](-)) by the addition of equimolar [Ln](-). The theoretical calculations supported the existence of the facial configuration. The coordinated water molecules of MLn(2) were detected by H-1 NMR spectroscopy and the acidity was estimated in the order of ML1(2) > ML2(2). Calcium afforded only the dinuclear complex, [Ca-2(L1)(2)(H2O)(5)(1,4-dioxane)] (Ca(2)L1(4)), which showed a low hydrolytic activity.