Synthetic, spectroscopic and structural studies on 4-aminobenzoate complexes of divalent alkaline earth metals: X-ray crystal structures of [{Mg(H2O)(6)}(4-aba)(2)]center dot 2H(2)O and [Ca(H2O)(2)(4-aba)(2)] (4-aba=4-aminobenzoate)

Abstract

Reactions between MCl2. nH(2)O (M = Mg, Ca, Sr, and Ba) and 4-aminobenzoic acid (4-abaH) result in the formation of complexes [{Mg(H2O)(6)}(4-aba)(2)]. 2H(2)O (1), [Ca(4-aba)(2)(H2O)(2)] (2), [Sr(4-aba)(2)(H2O)(2)] (3), and [Ba(4-aba)(2)Cl] (4), respectively. The new compounds 1 and 2, as well as the previously reported 3 and 4 form an extended intra- and intermolecular hydrogen bonded network in the solid-state. The compounds have been characterized by elemental analysis, pH measurements, thermogravimetric studies, and IR, NMR, and UV-Vis spectroscopy. The solid state structures of the molecules 1 and 2 have been determined by single crystal X-ray diffraction studies. In the case of magnesium complex 1, the dipositively charged Mg cation is surrounded by six water molecules and the two 4-aminobenzoate Ligands show no direct bonding to the metal ion. The calcium ion in 2 is octa-coordinated with direct coordination of the 4-aminobenzoate ligands to the metal ion. The Ca . . . Ca separation in the polymeric chain of 2 is 3.9047(5) Angstrom