Spin-crossover in dimeric hydrogen-bonded iron(II) 2-(pyrazolyl)-pyridine and 2-(imidazolyl)-pyridine complexes

Five new hydrogen-bonded solvated iron(H) complexes of pyrazolyl- and imidazolyl-based N,N-chelating ligands have been synthesised. Water to ligand-NH hydrogen-bonded bridges occur in the pseudo-dimeric complexes {cis-[Fe(pypzH)(2)(NCX)(2)](2)(-)(mu-OH2)(H2O)(2)) (.) (H2OMeOH)-Me-. (where X = S or Se), and in the chain complex {cis-[Fe(pypzH)(2)(NCS)(2)](mu-OH2)}(n). A "half" spin-crossover (T. = 125 K) was observed in the dimeric X = Se complex by means of magnetic measurements and no thermal hysteresis occurred between 4 and 300 K. The crystal structure at 123 K showed Fe-N distances consistent with the magnetism. Each Fe in the dimeric unit was structurally equivalent in the HS-LS state. Removal of the solvate molecules led to HS-HS behaviour over the temperature range 4-300 K. The pseudo-dimer with X = S also showed HS-HS behaviour as did the monomeric analogue cis[Fe(pypzH)(2)(NCS)(2)]H2O and a structurally different methanol-bridged dimer [cis-[Fe(pyimH)(2)(NCS)(2)](2)(mu-McOH)(2)} (.) 2MeOH (pypzH = 2-(1H-pyrazol-3-yl)-pyridine; pyimH = 2-(1H-imidazol-2-yl)-pyridine). (c) 2005 Elsevier Ltd. All rights reserved.