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 (original) (raw)

2001, Inorganic Chemistry

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 oxalatobridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(µ-ox)(2-ampy) 2 (M ) Co (1), Ni (2), Cu ) are isomorphous and crystallize in the monoclinic space group C2/c (No. 15), Z ) 4, with unit cell parameters for 1 of a ) 13.885(2) Å, b ) 11.010(2) Å, c ) 8.755(1) Å, and ) 94.21 , Ni (5), Cu ) 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 , b ) 12.935(3), and c ) 18.632(2) Å. Compound Co(µ-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) Å, b ) 5.484(1) Å, c ) 16.592(2) Å, and ) 117.76(1)°. Complexes M(µ-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 , and c ) 29.469(4) Å. 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 Å. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-cyclic 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.