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摘要
The reaction of 4-phenylimino-1,2,4-triazole (1) with Fe-II, Co-II, Ni-II and Cu-II thiocyanate produces a series of analogous dinuclear compounds of formula [M-2(1)(5)(NCS)(4)] (2-5) as demonstrated by single-crystal X-ray diffraction studies of the Fe-II (2) and Co-II (3) analogues. The magnetic properties of [Fe-2(1)(5)(NCS)(4)]center dot xMeOH (x = 3.5-5) reveal a partial and gradual spin crossover (SCO) centred at T-SCO = 115 K. This is confirmed by its crystal structure solved at 100, 150 and 250 K, which exhibits a gradual decrease of the Fe-N bond lengths with temperature. However, the bulk hydrated form of 2 that is generated upon exposure to air of crystals is a high-spin compound that exhibits weak antiferromagnetic interaction. The exchange coupling among the Fe-II S = 2 ions within the dinuclear neutral complex was evaluated as J/k(B) = -1.33(3) K by using the Heisenberg Hamiltonian H = -2JS(1)center dot S-2. Similarly, the magnetic properties of the Ni-II (4) and Cu-II (5) analogues are dominated by moderate and weak antiferromagnetic interactions evaluated as J/k(B) = -13.9(3) and -0.30(5) K, respectively. The presence of strong spin-or-bit coupling of the individual Co-II ions impeded the evaluation of the likely antiferromagnetic interaction that leads to a singlet ground state in 3. The reported structures of 2 and 3 are new additions to a very scarce family of dinuclear complexes bearing a unique triple N1,N2-triazole bridge. Owing to its relevance in the peculiar properties of 1D triazole-based SCO materials, which are widely studied for their various potential applications, a structural analysis of this triple N1,N2-triazole bridge in reported structures of Fe-II and Co-II trinuclear and 1D compounds is provided.
- 出版日期2013-2
