Crystal engineering of p-sulfocinnamic acid into mononuclear cationic Fe(ii), Co(ii) and Fe(iii) complexes

Abstract

In this work, we report the synthesis of two new Co(II) metal salts [Co(H₂O)₆](Hpsca)₂·nH₂O (n = 2, 4) incorporating a p-sulfocinnamic acid counter anion (Hpsca⁻). Together with the previously reported iron(II) analogue [Fe(H₂O)₆](Hpsca)₂·2H₂O, these precursors were utilized to synthesize four new coordination complexes [M(bipy)₃](Hpsca)₂·2MeOH (M = Fe (1), Co (2), bipy = 2,2′-bipyridine), [Fe(1-bpp)(Hpsca)(H₂O)(MeOH)]Hpsca·MeOH (3, 1-bpp = 2,6-di(1-pyrazolyl)pyridine) and [Fe(3,2,3-sal₂tet)]Hpsca·H₂O (4), 3,2,3-sal₂tet = 2,2′-((1Z,13Z)-2,6,9,13-tetraazatetradeca-1,13-diene-1,14-diyl) diphenol. Single crystal X-ray diffraction analyses revealed that all complexes consist of discrete mononuclear cationic units, while the Hpsca⁻ anion forms different supramolecular arrangements. ⁵⁷Fe Mössbauer spectroscopy confirms the low-spin state for Fe(II) ions in 1 and Fe(III) ions in 4, in accordance with crystallographic results. This work highlights the versatility of the Hpsca⁻ counteranion to stabilize diverse crystal architectures as well as its ability to couple solid-state reactivity and spin state modulation, thanks to the potential anion-driven light induced spin change based on the solid state [2 + 2] photodimerization of Hpsca⁻.