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

The reaction of M(ox). 2H(2)O (M = Co(II), Ni(II)) or K-2(Cu(ox)(2)). 2H(2) O (ox = oxalate dianion) with n-ampy (n = 2, 3, 4; n-ampy = n-aminopyridine ) and potassium oxalate monohydrate yields one-dimensional oxalato-bridged metal(II) complexes which have been characterized by FT-IR spectroscopy, va riable-temperature magnetic measurements, and X-ray diffraction methods. Th e complexes M(mu -ox)(2-ampy)(2) (M = Co (1), Ni (2), Cu (3)) are isomorpho us and crystallize in the monoclinic space group C2/c (No. 15), Z = 4, with unit cell parameters for 1 of a = 13.885(2) Angstrom, b = 11.010(2) Angstr om, c = 8.755(1) Angstrom, and beta = 94.21(2)degrees. The compounds M(mu - ox)(3-ampy)(2).1.5H(2)O (M = Co (4), Ni (5), Cu (6)) are also isomorphous a nd crystallize in the orthorhombic space group Pcnn (No. 52), Z = 8, with u nit cell parameters for 6 of a = 12.387(1), b = 12.935(3), and c = 18.632(2 ) Angstrom. Compound Co(mu -ox)(4-ampy)(2) (7) crystallizes in the space gr oup C2/c (No. 15), Z = 4, with unit cell parameters of a = 16.478(3) Angstr om, b = 5.484(1) Angstrom, c = 16.592(2) Angstrom, and beta = 117.76(1)degr ees. 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 f or 8 of a = 5.342(1), b = 17.078(3), and c = 29.469(4) Angstrom. All compou nds 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 in trachain distances in the range of 5.34-5.66 A. In all cases, the metal ato ms are six-coordinated to four oxygen atoms, belonging to two bridging oxal ato ligands, and the endo-cyclic nitrogen atoms, from two n-ampy ligands, b uilding distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibili ty measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in whic h a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous m agnetization below 8 K, which corresponds to the presence of spin canted an tiferromagnetism.