Synthesis, X-ray structures and magnetic properties of linear chain 4-cyanopyridine compounds: [Cu(4-CNpy)4(H2O)](ClO4)2 and M(4-CNpy)2Cl2 (M Mn, Fe, Co, Ni, Cu)

Abstract The synthesis, structures and magnetic properties of linear chain complexes of metal ions with 4-cyanopyridine are reported (4-CNpy=4-cyanopyridine): [Cu(4-CNpy) 4 (H 2 O)](ClO 4 ) 2 and M(4-CNpy) 2 Cl 2 (MMn, Fe, Co, Ni, Cu). All compounds crystallize in monoclinic systems. Crystallographic data for [Cu(4-CNpy) 4 (H 2 O)](ClO 4 ) 2 ] n ( 1 ): space group P 2 1 / c with a = 13.225(3), b = 10.567(2), c = 20.522(3) A , β = 99.71(2)°, V = 2826.7(9) A 3 , Z = 4, D calc = 1.640 Mg m −3 , μ = 3.430 mm −1 . The compound contains primer CuL 4 units with the ligands bounded to copper ions through the ring nitrogens. These units are weakly linked into chains through semi-coordinated bonds between the nitrile nitrogen and an adjacent copper ion via the axial sites. The magnetic data show only a weak antiferromagnetic interaction ( θ CW = −0.52(1) K). Crystallographic data for [Cu(4-CNpy) 2 Cl 2 ] n ( 2 ): space group P 2 1 / n with a = 3.779(2), b = 25.711(12), c = 7.104(4) A , β = 95.98(4)°, V = 686.48(4) A 3 , Z = 2, D calc = 1.658 Mg m −3 , μ = 5.575 mm −1 . Crystallographic data for [Mn(4-CNpy) 2 Cl 2 ] n ( 6 ): space group P 2 1 / c with a = 3.700(2), b = 7.198(2), c = 26.520(5) A , β = 92.13(3)°, V = 705.8(4) A 3 , Z = 2, D calc = 1.572 Mg m −3 , μ = 1.303 mm −1 . Both dichloride compounds similar structures, consisting of chains of metal ions bibridged by chlorides with the 4-CNpy ligands coordinated to the metal ions in the axial sites through the pyridine nitrogens. The difference in space groups is caused by the different modes of packing the chains into 3D lattices. Infrared spectra and powder X-ray diffraction patterns indicate that the remaining compounds form an isostructural series. The powder magnetic susceptibilities have been measured between 2 and 300 K for all compounds. Antiferromagnetic exchange (Cu, Mn) or ferromagnetic exchange (Ni, Co, Fe) exists within the chains. The Ni, Co and Fe compounds order antiferromagnetically at 7.2(2), 2.1(2) and 4.6(2) K, respectively. Magnetic field induced transitions have been observed in these three compounds below their ordering temperatures. The copper and manganese data have been fit to models for Heisenberg antiferromagnetic linear chain with S = 1 2 and S = 5 2 with exchange constants J Co / k = −13.7(2) K and J Mn / k = −0.5 7(1) K, respectively. The nickel and cobalt data have been fit to models for ferromagnetic linear chains, with the nickel compound corresponding to a S = 1 Heisenberg model with exchange constant J / lk = +4.8(2) K, and the cobalt compound to a S = 1 2 ferromagnetic Ising linear chain with exchange constant J / k = + 6.6(2) K. The iron data has not been successfully to fit to any model. It is concluded that the total magnetic interaction between the chains has been increased by approximately 50% by the substitution of 4-CNpy for pyridine.