Tris-Alkoxylphenylterpyridine Cobalt(II) Complexes: Synthesis, Structure, and Magnetic and Mesomorphic Behaviors

Two novel cobalt(II) complexes [Co(L1)(2)](BF4)(2)center dot CH3CN center dot 0.5H(2)O (1) and [Co(L2)(2)](BF4)(2) (2) (L1 = 4'-(3,4,5-trimethoxy-phenyl)-[2,2':6',2aEuro(3)]terpyridine, L2 = 4'-(3,4,5-tris-hexadecyloxy-phenyl)-[2,2':6',2aEuro(3)]terpyridine) have been synthesized, and their structural, magnetic and mesomorphic properties were characterized by single crystal X-ray diffraction (XRD) analysis, temperature-dependent magnetic susceptibility, POM, DSC, and powder XRD analysis. The molecular structure of the complex 1 with short alkyl substituents exhibited that the metal ion has an N-6 coordination sphere of distorted octahedral geometry and various intermolecular pi-pi interactions are important factors influencing the crystalline array. The magnetic behaviour of 1 displayed a typical of gradual spin transition for cobalt(II) terpyridine complexes. On the other hand, the complex 2 possessing linear long alkyl chains showed a gradual spin transition between low-spin and high-spin with a thermal hysteresis loop (T (1/2)a dagger = 338 and T (1/2)a dagger = 327 K) triggered by the crystal-to-mesophase transition. The powder XRD and POM analyses were indicative of the liquid crystalline lamellar phase of 2.