Cyanidometallates and Polyresorcinols: Wealth of Molecular Synthons, Structural Hierarchy, and Optical Properties

Crystal engineering focuses on the design of functional materials through the recognition and description of specific supramolecular synthons. In this study, we developed a series of centrosymmetric cocrystal salt solvates (PPh4)3[M(CN)6](L)n·msolv [M = Cr(III), Fe(III), Co(III); L = polyresorcinol coformers acting as multiple hydrogen bond donors: 3,3′,5,5′-tetrahydroxy-1,1′-biphenyl (DiR, n = 1) or tetrakis(3′,5′-dihydroxy-[1,1′-biphenyl]-4-yl)methane (TetraRB, n = 1.5)] denoted as MDiR′ and MTetraRB, respectively. Both architectures feature supramolecular trans-bis(chelated) {[M(CN)6]3–;(H2DiR)2(Hsolv)2} or {[M(CN)6]3–;(H2TetraRB)2(HTetraRB)2} motifs within their hydrogen-bonded subnetworks, alternative and complementary to the relevant cis-bis(chelated) motifs observed by us previously. MDiR′ phases appear due to the instability of previously reported noncentrosymmetric MDiR phases in crystallization mixtures, both architectures related as structural supramolecular isomers. MTetraRB crystals demonstrate the coexistence of the above-mentioned hydrogen-bonded synthons and linear arrangement of TetraRB coformers, controlled by their size, mutual interlocking, and peripheral TetraRBO–H···OTetraRB hydrogen bonds. The photoluminescent response is correlated with the dimensionality of hydrogen bonds and the extent of the π orbital system of L. A complete landscape of hydrogen-bonded synthon geometry, symmetry of crystal lattice, crystal stability, and optical properties involving the previous and current congeners to the series is provided to contribute to the roadmap of rational design and construction of functional materials.