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

Abstract

Readily soluble magnesium and zinc carboxylates [M(Ln)2(H2O)4] (MLn2) (M = Mg, Zn; L1 = O2C-2-Ar3CCONH-6-n-BuCONHC6H3; L2 = O2C-2-Ar3CCONHC6H4; Ar = 4-t-BuC6H4) containing intramolecular NH···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. (1)H NMR spectral measurements revealed a fast trans–cis isomerization of MLn2 in CDCl3, which was converted into a unique fac-[M(Ln)3(H2O)3]− (fac-[MLn3]−) by the addition of equimolar [Ln]−. The theoretical calculations supported the existence of the facial configuration. The coordinated water molecules of MLn2 were detected by (1)H NMR spectroscopy and the acidity was estimated in the order of ML12 > ML22. Calcium afforded only the dinuclear complex, [Ca2(L1)2(H2O)5(1,4-dioxane)] (Ca2L14), which showed a low hydrolytic activity.