Structurally characterized magnesium carboxylates with tuned melting points

Abstract

A novel family of carboxylic acid modified Mg species has been synthesized through the reaction of Mg(OEt) 2 with a series of sterically varied carboxylic acids (HORc) where HORc=HO 2CMe (HOAc), HO 2CCHMe 2 (HOPc), HO 2CCMe 3 (HOBc) and HO 2CCH 2CMe 3 (HONc). The resultant products were isolated as [Mg(OAc) 2] 3(HOAc) 2(H 2O) 2 · 2(HOAc) ( 1), [Mg(OPc) 2(HOPc)] 6 ( 2), Mg(OBc) 2(HOBc) 4 ( 3) and [Mg(ONc) 2(HONc)] 6 ( 4). Compound 1 is trinuclear wherein the two terminal octahedral (Oh) bound Mg metal centers possess one terminal water, one terminal, one unidentate bridging and two bidentate bridging OAc ligands that symmetrically bind to the central Oh bound Mg cation. The water in 1 is believed to be generated in situ through an esterification process. In contrast, each of the six Mg atoms of 2 or 4 adopt a trigonal bipyramidal geometry by coordinating one terminal and four bidentate bridging ORc ligands that yield a ring (diameter 6.54 Å for 2 and 6.57 Å for 4) of bridging ORc ligands. Compound 3 binds two terminal OBc ligands and four terminal HOBc ligands to yield a monomeric complex with no water present. Standard analytical data were obtained but did not add significant amounts of information concerning the bulk properties of 1– 4. Differential scanning calorimetry and thermal analysis indicated the melting point of these species was tunable.