Retention of single crystals of two Co(ii) complexes during chemical reactions and rearrangement

Abstract

Monomeric [Co^II(hep-H)(H₂O)₄]SO₄ [1]SO₄ and [Co^II(hep-H)₂(H₂O)₂](NO₃)₂ [2](NO₃)₂ have been developed from 2-(2-hydroxyethyl)pyridine (hep-H) and CoSO₄·7H₂O/Co(NO₃)₂·6H₂O, respectively, at 298 K. On exposure to heat (120 °C), the light orange single crystal of [1]SO₄ transforms to a pink single crystal corresponding to the neutral sulfato bridged dimeric complex [(Co^II(hep-H)(H₂O)₂(μ₂-sulfato-O,O′))₂](3). However, the orange single crystal of [2](NO₃)₂ transforms to the single crystal of monomeric [Co^II(hep-H)₂(NO₃)]NO₃ [4]NO₃ (orange) upon exposure to heat (110 °C) where one of the NO₃⁻ counter anions in [2](NO₃)₂ moves to the coordination sphere. The facile SCSC transformations of [1]SO₄ (orange) → 3 (pink) and [2](NO₃)₂ (orange) → [4]NO₃ (orange) involve intricate multiple bond breaking and bond forming processes without losing the crystallinity. Moreover, the immersion of the pink single crystal of 3 in 1 N HCl results in a green single crystal of ionic monomeric [Co^II(H₂O)₆]·SO₄[5]SO₄, which indeed demonstrates the unprecedented unique two-step SCSC transformations.