Supramolecular Assemblies in Silver Complexes: Phase Transitions and the Role of the Halogen Bond

Weak interactions (hydrogen bonds, halogen bonds, CH···π and π-π stacking) can play a significant role in the formation of supramolecular assemblies with desired structural features. In this contribution, we report a systematic investigation on how a halogen bond (XB) can modulate the structural arrangement of silver supramolecular complexes. The complexes are composed of X-phenyl(bispyrazolyl)methane (X = Br, I) and I-alkynophenyl(bispyrazolyl)methane ligands functionalized in meta (L^3Br, L^3I) and para (L^4Br, L^4I, L^4CCI) positions on a phenyl ring with the purpose of providing different directionalities of the X function with respect to the N,N coordination system. The obtained [Ag(L)₂]⁺ moieties show remarkable geometric similarities, and the L^4Br, L^4I, and L^4CCI ligands exhibit the most conserved types of supramolecular arrangement that are sustained by XB. The increased σ-hole in L^4CCI with respect to L^4I leads to an occurrence of short (and strong) XB interactions with the anions. [Ag(L^4I)₂]PF₆ and [Ag(L^4I)₂]CF₃SO₃ are characterized by the presence of three different phases, and the single-crystal evolution from phase-1 (a honeycomb structure with large 1D cavities) to phase-3 (solventless) occurs by a stepwise decrease in the crystallization solvent content, which promotes an increase in XB interactions in the lattice. The present paper aims to provide useful tools for the selection of appropriate components for the use of coordination compounds to build supramolecular systems based on the halogen bond.