The preparation and characterization of a novel chiral macrocycle S,S-ijFe II IJPhCH 2 OCH 2 ) 2 IJN 3 O 2 )IJCN) 2 ] (4) is presented. Magnetic susceptibility studies reveal that this complex undergoes a gradual spin crossover in the solid state with no thermal hysteresis. Variable temperature X-ray diffraction studies on single crystals of 4 reveal that at 150 K the complex is comprised of two crystallographically independent octahedral FeIJII) centres. Warming the crystal to 300 K results in a subtle change in coordination geometry of one of the octahedral FeIJII) centers towards a 7-coordinate, pentagonal bipyramidal geometry that is accompanied by a conformation change in one of the PhCH 2 OCH 2 substituents. CrystEngComm This journal isScheme 1 Structural changes in coordination geometry of the FeIJII) centre of the parent ijFeIJN 3 O 2 )IJCN) 2 ] complex (1) on cooling and warming. 3

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