Abstract

Three iron(III) complexes, [Fe(qnal)<inf>2</inf>]Y {qnal = 1-[(8-quinolinylimino)methyl]-2-naphthalenolate; Y = NO<inf>3</inf> 1, BPh<inf>4</inf>·CH<inf>2</inf>Cl<inf>2</inf> 2, NCS 3} have been prepared to explore anion effects in spin crossover systems. Structural studies on 2 reveal supramolecular chains formed by π–π and C–H···π interactions between the [Fe(qnal)<inf>2</inf>]⁺ cations. Magnetic susceptibility measurements show the onset of spin crossover in 1 above 200 K, while complete spin crossover is observed in 2 and 3 with T<inf>1/2</inf> = 285 and 340 K, respectively. Unusually, 2 also undergoes light-induced excited spin state trapping (LIESST) at 980 nm with ca. 65 % efficiency and T(LIESST) = 25 K and reverse-LIESST at 660 nm with full reversibility over many cycles. The results highlight the important influence that the anion has on thermal and light-activated spin crossover properties.