Crystallographic Evidence for Reversible Symmetry Breaking in a Spin‐Crossover d⁷ Cobalt(II) Coordination Polymer

Abstract

All in a spin: A cobalt(II) coordination polymer has a highly cooperative spin‐crossover (SCO) behavior with a small hysteresis loop (see picture; HS=high spin, LS=low spin). The correlation of the magnetic properties with the crystal structures was determined at different temperatures. This study reveals an unprecedented reversible symmetry breaking in a d7 SCO coordination polymer.

Counter anion dependent gradual spin transition in a 1D cobalt(ii) coordination polymer

“…It is worth mentioning that the anion⋯π interaction involving the O atom of ClO 4 − and π-cloud of the dca unit, which is most likely responsible for the small hysteresis loop 13 in 1·ClO 4 , is absent in 1·PF 6 . 13 Such behaviour suggests an efficient cooperative effect among adjacent Co(II) centres along the 1D supramolecular chains and between the chains through interchain interactions as well. 2).…”

“…To extend such work, herein we present the isolation, structures (room and low) and magnetic properties of another 1D Co(II) coordination polymer, [Co(enbzpy)(µ 1,5 -dca)] n (PF 6 ) n (1·PF 6 ), which shows a gradual SCO behaviour reflecting a remarkable change in properties just by changing magnetically innocent counter anions. On the other hand, the asymmetric unit in 1·ClO 4 LT contains four crystallographically different Co(II) centres (Co1A, Co1B, Co2A and Co2B) with coordination environment of each metal(II) centre analogous 13 to the Co(II) centre in 1·ClO 4 † X-ray structural analyses ‡ of the new compound were successfully carried out at 298 K (1·PF 6 RT ) and 100 K (1·PF 6 LT ).…”

Spin state switching in iron coordination compounds

“…In certain cases, abrupt spin transitions with hysteresis effects, whose width is strongly dependent on the type of molecular bridge between iron(II) sites as well as on crystal packing considerations, are observed. A few examples of iron(III) and cobalt(II) SCO CPs have also been described [272–275]. In this section, we review prototype materials as well as highlight recent examples of CPs and MOFs constructed from ligands based on organic molecules.…”

Synthesis, structure and characterization of two new Zn(II) and Cd(II) complexes with the bidentate ligand 2-[(2-aminoethyl)amino]ethanaminium (AEEA)

“…Variable bonding, such as the ligands' ability to coordinate to a metal atom in mono-, bi-or polydentate fashions, their ability to bridge between metal ions, or to steer the coordination environment of the central atom are what allows for the immense structural possibilities in metal coordination chemistry, which in turn is central to the extremely diverse use of metal complexes in all kinds of applications [1,2]. Among ligands commonly used in coordination chemistry, Schiff bases are an extremely important class, thanks to their facile synthesis, and their easily tunable steric and electronic properties [3,4]. They are known to be a class of versatile ligands, capable of generating a variety of molecular architectures and coordination polyhedra [5][6][7].…”