Syntheses, structures and properties of alkaline-earth metal salts of 4-nitrophenylacetic acid

Abstract

The synthesis, crystal structure, spectral characteristics and thermal properties of alkaline-earth metal salts of 4-nitrophenylacetic acid (4-npaH) namely, [Mg(H sub(2)O) sub(6)](4-npa) sub(2).4H sub(2)O (4-npa = 4-nitrophenyl-acetate) (1), [Ca(H sub(2)O) sub(2)(4-npa) sub(2)] (2) and [Sr(H sub(2)O) sub(3)(4-npa) sub(2)].4.5H sub(2)O(3) are reported. In 1, the 4-npa ion functions as a charge balancing counter anion for the octahedral [Mg(H sub(2)O) sub(6)] sup(2+) unit with the Mg(II) ion situated on a centre of inversion. The two unique lattice water molecules link the [Mg(H sub(2)O) sub(6)] sup(2+) cations and 4-npa anions with the aid of O-H...O interactions. Compounds 2 and 3 are one-dimensional (1-D) coordination polymers containing an eight coordinated Ca(II) situated in a general position and a nine coordinated Sr(II) located on a twofold axis. The mu2-bridging tridentate binding modes of the crystallographically independent 4-npa ligands in 2 and the unique 4-npa ligand in 3 link the bivalent metal ions into an infinite chain with alternating Ca...Ca separations of 3.989 and 4.009 Angstrom, respectively, and a single Sr...Sr separation of 4.194 Angstrom in the 1-D chain.