Synthesis, structure and magnetic properties of tetrakis-mu-carboxylato-bis(dodecylnicotinato)dicopper(II) complexes; crystal and molecular structureof the decyl carboxylate derivative

Dodecylnicotinate bis-adducts of binuclear copper carboxylates, of the gene ral formula Cu-2(O2CCn-1H2n-1)(4)(C5H4NCOOC12H25)(2), were synthesized for n = 10, 12, 14, 16, 18 and 20, and their crystal structure, thermal behavio r and magnetic properties studied. The molecular structure of the decyl der ivative has been determined from single-crystal X-ray diffraction data. The dimer is centrosymmetric with the Cu II ions in a square-pyramidal coordin ation with four O-alkyl O atoms [average d(Cu-O) 1.960 (6) Angstrom] in the basal plane and the nicotine N atom at apical positions [d(Cu-N) 2.183 (3) Angstrom]. The copper ions, 2.615 (1) Angstrom apart, are bridged by four O-alkyl carboxylate groups. Both the n = 20 and n = 18 homologues exhibit l amellar phases, which can be related to the supramolecular arrangement foun d in the n = 10 derivative. The magnetic behavior of the decyl and octadecy l dimers was studied in the 2-300 K temperature range. They exhibit a stron g intramolecular antiferromagnetic interaction (Cu-Cu superexchange couplin g constant J = -347 cm(-1) for the decyl derivative), which can be attribut ed to a large overlap of the metal 3d orbitals and the oxygen lone pair orb itals of the linking carboxylate groups.