Novel Malonate-Containing Coordination Compounds with Ligands Having N- and NO-Donors: Synthesis, Structures, and Magnetic Properties

In our efforts to tune the structures of mixed-ligands malonate-containing coordination compounds, four copper(II) and two high-spin cobalt(II) complexes of formulas [Cu(mal)(H2O)(dpo)](n) (1), [Cu-2(mal)(2)(H2O)(2)(dpp)](n)center dot 7nH(2)O (2), [Cu-2(mal)(2)(H2O)(2)(bpe)](n) center dot 2nH(2)O (3), {[Cu(mal)(2)(H2O)(2)][Cu(dien)]}(n)center dot 4nH(2)O (4) [Co-2(mal)(2)(H2O)(6)(dpo)]center dot 2H(2)O (5) and [Co(mal)(H2O)(phen)](n)center dot 2nH(2)O (6) [H(2)mal = malonic acid, dpo 4,4'-bipyridine-N,N'-dioxide, dpp = 2,3-bis(pyridyl)pyrazine, bpe =1,2-bis(4-pyridyl)ethylene, dien = diethylenetriamine and phen = 1,10-phenanthroline] have been synthesized and structurally characterized by X-ray diffraction on single crystals. Complexes 1, 2, 4, and 6 are chain compounds, 5 is a dinudear species, and 3 has a sheet-like structure. The malonate ligand in this family acts as either a blocking (1 and 5) or bridging ligand (2-6). The rod-like molecules dpo (1 and 5) and bpe (3) exhibit the bis-monodentate (1 and 3) and monodentate (5) coordination modes, whereas dpp (2), dien (4), and phen (6) act as bis-bidentate (2), tridentate (4), and bidentate (6) ligands. The neutral motifs of 1-6 are interlinked through hydrogen bonds and weak C H " " " r and n ii type interactions affording supramolecular three-dimensional networks. Variable-temperature magnetic susceptibility measurements show the occurrence of weak ferro- (2, 3, 5, and 6) and antiferromagnetic (1 and 4) interactions, the exchange pathways being the carboxylatemalonate (3-6), oxo-carboxylate (2), bis-bidentate (dpp) (2) or hydrogen bonds (1). Remarkably, the equatorial-apical exchange pathway through the carboxylate bridge present in 4 provides the first case of the occurrence of an antiferromagnetic interaction in a malonate-containing copper(II) complex.