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

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 center dot 7H(2)O/Co(NO3)(2)center dot 6H(2)O, respectively, at 298 K. On exposure to heat (120 degrees 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)(mu(2)-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 degrees 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)]center dot SO4[5]SO4, which indeed demonstrates the unprecedented unique two-step SCSC transformations.