Ferromagnetic Coupling Through the End-to-End Thiocyanate Bridge in Cobalt(II) and Nickel(II) Chains

The preparation, spectroscopic characterization, and X-ray crystal structure of two novel one-dimensional compounds of formula [M-II(tppz)(NCS)(mu-1,3-NCS)](n) [tppz = 2,3,5,6-tetrakis(2-pyridyppyrazine and M = Co(1) and Ni (2)] are reported. 1 and 2 are isomorphous compounds, and they crystallize in the P2(1)/n space group. Their structures are made up of zigzag chains of cobalt(II) (1) and nickel(II) ions (2) bridged by single end-to-end thiocyanate groups with a tridentate tppz molecule and a terminally bound thiocyanate-N ligand achieving distorted MN5S octahedral surroundings around each metal center. The main source of the distortion of the ideal octahedron is due to the geometrical constraints issued from the occurrence of two fused five-member chelate rings of the tridentate tppz ligand, the values of the N-M-N bond angles covering the range 75.58(9)-78.66(9)degrees. The M-N bond lengths vary in the range 2.025(3)-2.116(29 (1) and 2.001(2)-2.079(2) angstrom (2), and they are shorter than the M-S bond distance [2.6395(10) (1) and 2.5225(9) angstrom (2)]. The values of the intrachain metal-metal separation are 6.4197(7) (1) and 6.3257(5) angstrom (2). The magnetic properties of 1 and 2-have been investigated in the temperature range 1.9-300 K. Both compounds exhibit intrachain ferromagnetic interactions with values of the magnetic coupling (J) of +4.60 (1) and +7.82 cm(-1) (2) [the spin Hamiltonian being defined as (H) over cap = -J Sigma(n-1)(i=1)(S) over cap (i)(S) over cap (i+1)].