Synthesis, structure, and magnetic properties of three new one-dimensionalnickel(II) complexes: New magnetic model for the first one-dimensional S=1complex with alternating ferro-ferromagnetic coupling

Three new one-dimensional nickel(Ii) complexes with the formulas trans-[Ni( N-Eten)(2)(mu (1,3)-N-3)](n)(ClO4)(n) (1), trans-[Ni(N-Eten)(2) (mu (1,3)-N -3)](n)(PF6)(n) (2) and cis-[Ni(N-Eten)(mu (1,1)-N-3)(2)]n (3) (N- Eten =N- Ethylethylenediamine) were synthesized and characterized. Complex 1 has the P2(1)/c space group and consists of a structurally and magnetically altern ating one-dimensional antiferromagnetic system with end-to-end azido bridge s. Compound 2 has the P (1) over bar space group and has alternate units in its structure but consists of a magnetically uniform one-dimensional antif erromagnetic system with end-to-end azido bridges. Complex 3 has the 12/a s pace group and may be described as a structurally and magnetically alternat ing one-dimensional ferromagnetic system with double azido bridged ligands in an end-on coordination mode. The chi T-M versus T plots for compound 3 s uggest an intramolecular ferromagnetic interaction between adjacent Ni-II i ons and metamagnetism at low temperature (below 10 K). The magnetization me asurements versus applied field confirm this metamagnetic ordering. In orde r to describe the magnetic data of this compound we developed a general for mula for the magnetic susceptibility of the isotropic ferro-ferromagnetic S =1 Heisenberg chain in terms of the alternation parameter a (=J(2)/J(1)); t his assumed a variation of chi T-M versus the length N.