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

Abstract

Two novel cobalt(II) complexes [Co(L1)2](BF4)2·CH3CN·0.5H2O (1) and [Co(L2)2](BF4)2 (2) (L1 = 4′-(3,4,5-trimethoxy-phenyl)-[2,2′:6′,2″]terpyridine, L2 = 4′-(3,4,5-tris-hexadecyloxy-phenyl)-[2,2′:6′,2″]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 N6 coordination sphere of distorted octahedral geometry and various intermolecular π–π 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↑ = 338 and T 1/2↓ = 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.