Steric Trapping of the High Spin State in FeIII Quinolylsalicylaldimine Complexes

A new sterically bulky Schiff base ligand, N-(8-quinolyl)-5-tert-butylsalicylaldimine (Hqsal-5-tBu) has been prepared and a series of FeIII complexes, [Fe(qsal-5-tBu)2]Y (Y = Cl 1, ClO4 2, NO3 3, BF4 4) utilising this ligand are reported and fully characterised. UV-vis spectroscopic and electrochemical studies indicate that 1–4 are high spin (HS) in solution at room temperature and further suggest that the tBu group only slightly alters the electronic properties of 1–4 compared with related [Fe(qsal-5-X)2]+ systems. The structures of [Fe(qsal-5-tBu)2]Cl·4MeOH·H2O 1, [Fe(qsal-5-tBu)2]ClO4·MeOH 2, and [Fe(qsal-5-tBu)2]NO3 3 determined at 100 K reveal HS FeIII centres in all cases. Four-fold parallel aryl embraces and π–π interactions serve to link the cations forming 2D sheets mirroring the motifs found in other [Fe(qsal-5-X)2]+ complexes. Despite this the tBu group causes strong distortions at the Fe centre which as magnetic studies reveal prevent spin crossover trapping 1–4 in the HS state.

Stepped spin crossover in Fe(iii) halogen substituted quinolylsalicylaldimine complexes

Four iron(iii) spin crossover complexes with halogen substituted ligands are reported. The halogen is correlated with T_1/2 and controls the degree of spin crossover while extensive C–H⋯X and X⋯π interactions increase cooperativity.