Temperature induced spin crossover behaviour in mononuclear cobalt(II) bis terpyridine complexes

Dicationic cobalt(II) complexes of the type [Co( fterpy ) 2 ]c(X) 2 ·nH 2 O·mCH 3 OH ( fterpy = 4′-(2-furyl)-2,2′:6′,2″-terpyridine; 1 : X = PF 6 - , n = 1.5, m = 0; 2: X = ClO 4 - , n = 1, m = 1) have been isolated using self-assembly method and characterized by various spectroscopic techniques. In crystalline states both compounds exhibit gradual and incomplete spin crossover (SCO) behaviour in the temperature range 2-320 K. Various spin states of cobalt(II) in 1 have been confirmed by crystallographic evidences at 150 K and 293 K. A variation in counter anions and solvent molecules from 1 to 2 substantially improves the cooperativity among the spin active metal centres and thereby changing the nature of SCO behaviour.