Organosulfonate‐Modulated Spin‐Crossover Behavior in Three Halogen‐Functionalized Cobalt(II) Complexes

We reported the tunable spin-crossover (SCO) behavior in a series of halogen-functionalized cobalt(II) complexes constructed by the [Co(Brphtpy)₂]²⁺ SCO active units and various organosulfonates.

Abstract

We present here the syntheses, crystal structures, and spin crossover (SCO) properties of a series of halogen-functionalized cobalt(II) complexes, [Co(Brphtpy)₂](OTf)₂ ⋅ DMF ⋅ 2H₂O (1), [Co(Brphtpy)₂](HBS)₂ ⋅ H₂O (2), [Co(Brphtpy)₂](MQ)₂ ⋅ 2MeCN ⋅ 3H₂O (3) (Brphtpy=4′–(4-Bromophenyl)–2,2′:6′,2′′-terpyridine; OTf⁻=trifluoromethanesulfonate; HBS⁻=hydroxybenzenesulfonate dihydrate; MQ⁻=methyl orange). Variable-temperature single-crystal X-ray analyses revealed mononuclear compounds of 1–3 consisted of [Co(Brphtpy)₂]²⁺ SCO active units and organosulfonate anions and no structural phase transformation happened in measured high-low temperature. The packing structures of these complexes were tuned by varying organosulfonates. However, no notable supramolecular interactions can be found, in turn leading to gradual, incomplete, and non-hysteretic SCO behaviors. Interestingly, the SCO behaviors of these three complexes were significantly modified after the removal of lattice solvents. Combined structural and magnetic investigations revealed the non-cooperative supramolecular packing structures, guest internal pressure, and the small structural distortions of the SCO units should be responsible for the worse SCO properties of 1–3. The foregoing results show that to achieve high-performance Co²⁺ SCO, both the weak interactions, internal pressure, and structural distortion should be considered during the design and construction of SCO complexes.

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