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.

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…[87,112,[261][262][263][264][265] In most cases, ligands with strong RAHB systemsh ave lower reactivity towards metal ions, [55] but in some cases am etal ion can directly deprotonate the ligand, destroying the RAHB system and enteringt he chelating pocket. [87,112,[261][262][263][264][265] In most cases, ligands with strong RAHB systemsh ave lower reactivity towards metal ions, [55] but in some cases am etal ion can directly deprotonate the ligand, destroying the RAHB system and enteringt he chelating pocket.…”

“…Apart from the crucial contribution of RAHB for the synthesis of organic species, some recent studies have indicated a significant role of this type of hydrogen bonding in the preparation and design of coordination and organometallic compounds . In most cases, ligands with strong RAHB systems have lower reactivity towards metal ions, but in some cases a metal ion can directly deprotonate the ligand, destroying the RAHB system and entering the chelating pocket .…”

Synthesis, Characterization, and Low-Toxicity Study of a Magnesium(II) Complex Containing an Isovanillate Group

“…Furthermore, increased attention has also been directed to the contribution of hydrogen bonds in the control of coordinated water acidity . Recent studies have explored this in detail in a series of magnesium carboxylate complexes containing intramolecular NH···O hydrogen bonds using theoretical calculations and X-ray analysis. − …”