Syntheses, Crystal Structures, and Magnetic Properties of One-Dimensional Oxalato-Bridged Co(II), Ni(II), and Cu(II) Complexes with n-Aminopyridine (n = 2-4) as Terminal Ligand

摘要

The reaction of M(ox)·2H_2O (M = Co(II), Ni(II)) or K_2(Cu(ox)_2)·2H_2O (ox = joxalate dianion) with n-ampy (n = 2, 3, 4; n-ampy = n-jaminopyridine) and potassium oxalate monohydrate yields one-dimensional oxalatobridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(#mu#-ox)(2-ampy)_2 (M = Co (1), Ni (2), Cu(3)) are isomorphous and crystallize in the nomoclinic space group C2/c (No. 15), Z = 4, with unit cell parameters for 1 of a = 13.885(2) A, b = 11.010(2) A, c = 8.755(1) A, and #beta# = 94.21(2) deg. The compounds M(#mu#-ox)(3-ampy)_2·1.5H_2O (M = Co (4), Ni (5), Cu(6)) are also isomorphous and crystallize in the orthorhombic space group Pcnn (No. 52), Z = 8, with unit cell parameters for 6 of a = 12.387(1), b = 12.935(3), and c = 18.632(2) A. Compound Co(#mu#-ox)(4-ampy)_2 (7) crystallizes in the space group C2/c (No. 15), Z = 4, with unit cell parameters of a = 16.478(3) A, b = 5.484(1) A, c = 16.592(2) A, and #beta# = 117.76(1) deg. Complexes M(#mu#-ox)(4-ampy)_2 (M = Ni (8), Cu(9)) crystallize in the orthorhombic space group Fddd (No. 70), Z = 8, with unit cell parameters for 8 of a = 5.342 (1), b = 17.078(3), c = 29.469(4) A. All compounds are comprised of one-dimensional chains in which M(n-ampy)_2~(2+) units are sequentially bridged by bis-bidentate oxalato ligands with M…M intrachain distances in the range of 5.34-5.66 A. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-yclcic nitrogen atoms, from two n-ampy ligands, building distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibility measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in which a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous magnetization below 8 K, which corresponds to the presence of spin canted antiferromagnetism.