Magneto-structural correlations in one-dimensional Ni(en)2Pd(CN)4: magnetic properties and redetermination of the crystal structure at two temperatures

The magneto-structural correlations in Ni(en)2Pd(CN)4 (NEPC) have been studied. The crystal structure is formed by infinite electroneutral 2,2-TT type chains [&z.sbnd;Ni(en)2&z.sbnd;NC&z.sbnd;Pd(CN)2&z.sbnd;CN&z.sbnd;] (en<f>=1</f>,2-diaminoethane) in which the paramagnetic nickel atoms are bridged by diamagnetic tetracyanopalladate anions. Contrary to the previous room temperature X-ray analysis of NEPC, the results of the current structure determinations at both 293 and 150 K showed the nickel atom to be coordinated in the form of slightly elongated octahedron with two chelate bonded and disordered en molecules in the equatorial plane (mean Ni&z.sbnd;N distance of 2.096 A˚ at both temperatures) and N-bonded bridging cyano groups in the axial positions (Ni&z.sbnd;N distances of 2.117 and 2.108 A˚ at 293 and 150 K, respectively). Consequently, the zero field splitting parameter <f>D</f> is finite and positive. The chains are held together by weak hydrogen bonds of the N&z.sbnd;H⋯N(&z.tbnd;C) type. Magnetisation, susceptibility and specific heat measurements indicate that NEPC represents an <f>S=1</f> Heisenberg magnetic chain characterised by strong planar anisotropy, <f>D/kB&ap;5</f> K, weak in-plane anisotropy, <f>E/D=0.1</f>, and by a small exchange coupling constant, <f>J/kB&ap;0.25</f> K. These properties are similar to those exhibited by an analogous compound Ni(en)2Ni(CN)4. [Copyright &y& Elsevier]