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), [Cu₂(mal)₂(H₂O)₂(dpp)]_n·7nH₂O (2), [Cu₂(mal)₂(H₂O)₂(bpe)]_n·2nH₂O (3), {[Cu(mal)₂(H₂O)₂][Cu(dien)]}_n·4nH₂O (4) [Co₂(mal)₂(H₂O)₆(dpo)]·2H₂O (5) and [Co(mal)(H₂O)(phen)]_n·2nH₂O (6) [H₂mal = 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 dinuclear 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···π and π–π 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 carboxylate-malonate (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.