Influence of the Solvent Nature on the Spin Equilibrium in Solutions of the Cobalt(II) Phenylborate Hexa-n-Butylsulfide Clathrochelate by the Paramagnetic NMR Spectroscopy Data

The spin state of the cobalt(II) phenylborate hexa-n-butylsulfide clathrochelate in solutions is studied by paramagnetic NMR spectroscopy. This cage complex is shown to undergo the temperature-induced spin transition in solvents of different nature (acetonitrile, chloroform, dichloromethane, and benzene). The previously developed method for an analysis of paramagnetic shifts in NMR spectra allows the determination of the thermodynamic parameters (enthalpy and entropy) of the spin equilibrium in the solutions. In spite of the conformational rigidity of the macrobicyclic tris(dioximate) molecules, substantial changes in the electronic structures and spin equilibrium parameters are observed depending on the polarity of the solvent used. This provides opportunities for fine tuning of spin switch characteristics by changing this parameter of the medium.