Macrocycle-Based Spin-Crossover Materials

New iron(II) complexes of formula [Fe(L1)](BF4)2 (1) and [Fe(L2)](BF4)2·H2O (2) (L1 = 1,7-bis(2′-pyridylmethyl)-1,4,7,10-tetraazacyclododecane; L2 = 1,8-bis(2′-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized by infrared spectroscopy, variable-temperature single-crystal X-ray diffraction, and variable-temperature magnetic susceptibility measurements. The crystal structure determinations of 1 and 2 reveal in both cases discrete iron(II) monomeric structures in which the two functionalized tetraazamacrocycles (L1 and L2) act as hexadentate ligands; the iron(II) ions are coordinated with six nitrogen atoms: four from the macrocycle and two from two pyridine groups occupying two cis positions around the metal ion. In 1, the N−Fe−N bond angles indicate that the Fe(II) ion adopts an unusual distorted trigonal prismatic geometry. In agreement with the observed paramagnetic behavior, the average of the six Fe−N distances at 293 K (2.218(6) A) and at 90 K (2.209(2) A) corre...