Mesogenic and magnetic behavior in cobalt(II) and iron(II) compounds with long alkyl chains

Abstract

Metal complexes with long alkyl chains [Co(C16-terpy)3](BF4)2 (1), [Fe(C16-terpy)2](BF4)2 (2), [Co(C16-terpy)2](BPh4)2 (3), [Co(C14-terpy)2](BF4)2 (4), and [Fe(C12C10C5-terpy)2](BF4)2 (5) were synthesized and their physical properties characterized, where C16-terpy, C14-terpy, and C12C10C5-terpy are 4′-hexadecyloxy-2,2′:6′,2′′-terpyridine, 4′-tetradecyloxy-2,2′:6′,2′′-terpyridine, and 4′-5′′′-decyl-1′′′-heptadecyloxy-2,2′:6′,2″-terpyridine, respectively. Complexes 1, 2, and 5 exhibited liquid–crystal properties in the temperature ranges of 371–528 K and 466–556 K, and 88–523 K, respectively. Variable-temperature magnetic susceptibility measurements revealed that the Co(II) complexes 1 and 4 exhibited unique spin transitions (T 1/2↓ = 217 K and T 1/2↑ = 260 K for 1 and T 1/2↓ = 250 K and T 1/2↑ = 307 K for 4), so-called ‘reverse spin transition,’ induced by structural phase transitions. Complex 3 exhibited gradual spin-crossover behavior (T 1/2 = 160 K.), and complex 5 exhibited spin transitions (T 1/2↑ = 288 K and T 1/2↓ = 284 K) at the liquid crystal transition temperature. Compounds with multifunction, i.e., magnetic and liquid–crystal properties, are important in the development of molecular materials.