NH/π interaction in a spin-crossover complex [FeII(HLMe)2](BPh4)2•2CH3CN (BPh4-= tetraophenylborate; HLMe=2-methylimidazol-4-yl-methylideneamino-2-ethylpyridine)

Three Fell complexes, [Fe(HLR)(2)](BPh4)(2)center dot solvent (R = H, Me, Ph), were synthesized, where BPh4- = tetraphenylborate and HLR = 2-substituted-imidazol-4-yl-methylideneamino-2-ethylpyridine. The magnetic susceptibility measurements in 5-300 K revealed that [Fe(HLH)(2)]center dot(BPh4)(2)H2O (1), [Fe(HLMe)(2)](BPh4)(2)center dot CH3CN (2), and [Fe-(H L-Ph)(2)](BPh4)(2)center dot CH3CN (3) are low-spin (LS), spin-crossover (SC), and high-spin (HS) Fe-II complexes, respectively, indicating that the spin state can be effectively tuned by the bulkiness of the substituent. Complex 2 shows a steep SC around 250 K, where it assumes a cyclic structure of {[Fe(HLMe)(2)]BPh4}(2) constructed by four NH/pi bonds between the imidazole group and the phenyl ring of BPh4- in the HS state and a deformed structure with NH/,7 bonds and linear CH3CN center dot center dot center dot HN hydrogen bonds at the terminals in the LS state.