Probing the structural changes accompanying a spin crossover transition in a chiral [Fe(ii)(N₃O₂)(CN)₂] macrocycle by X-ray crystallography

Abstract

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

Spin States of Homochiral and Heterochiral Isomers of [Fe(PyBox)2]2+ Derivatives

“…Alternatively, chiral materials based on achiral SCO molecules have been prepared through doping them into chiral host frameworks, or crystallizing them with chiral counterions . However, chiral‐at‐molecule SCO compounds are rare, with most studies involving just two series of iron(II) complexes: a family of bidentate Schiff base complexes formed from chiral amines; and, a macrocyclic ligand with an asymmetric pattern of backbone substituents . The influence of chirality on the SCO properties of such compounds has only recently begun to be investigated and, importantly, all data published thus far have been measured in the solid state .…”

Design and Study of Structural Linear and Nonlinear Optical Properties of Chiral [Fe(phen)3]2+Complexes

“…Notably, we have been investigating the combination of SCO and chirality for some years now, 26 a combination sometimes obtained by serendipity 27 and obtained rationally only using optically active ligands. [27][28][29][30][31][32][33][34] Due to their extensively studied photophysics, the model complexes [Fe(bipy)3] 2+ , [Fe(phen)3] 2+ , or [Fe(terpy)2] 2+ were evident targets for attractive low-cost non-centrosymmetric materials showing non-linear optical properties, and for the study of their eventual dependence with the spin state of the complex. Indeed some data were recently published on a SCO compound, but puzzlingly the reported crystalline structure is centrosymmetric, and the magnitude of the effect reported was quite weak.…”

Spin-crossover materials: Getting the most from x-ray crystallography

“…The chirality functionality, if interrelated to the SCO behavior, offers remarkable potential properties and applications such as electro-optic effects, nonlinear optical properties, chiroptical switching, magneto-optic properties, spin filtering or spin polarization in molecular spintronics. 52,53 The chiral functionality may emerge from different possibilities : use of chiral ligands (such as macrocyclic ligands with asymmetric substituents) in a mononuclear complex, 54 use of chelating ligands which twist around the metal center (such as for the [Fe(phen) 3 ] complex), 52,53,55 confining SCO molecules in chiral host framework, 56 or co-crystalizing SCO molecules with chiral counterions. 57 Chiral SCO materials of different architectures have been reported…”

“…in the literature: chiral SCO metal-organic frameworks, 58 chiral SCO mononuclear complexes [52][53][54][55]57 , chiral SCO polymeric chains. 59 Synthesis with equimolar racemic composition of the two enantiomers usually pack in a centrosymmetric space group, or crystallize as inversion twins.…”