Silver complexes of 1,1′,3,3′-tetrakis(pyrazol-1-yl)propane: the “quadruple pyrazolyl embrace” as a supramolecular synthon

Abstract

The reaction between pyrazole and malonaldehyde bis(dimethylacetal) yields the first linked bis(pyrazolyl)methane ligand, CH₂[CH(pz)₂]₂. Reaction of this ligand with Ag(O₃SCF₃) yields [Ag₂{μ-CH₂[CH(pz)₂]}₂](SO₃CF₃)₂ (1). In the solid state 1 contains a dimeric dication in which two ligands sandwich two silver cations forming a bicyclic sixteen-membered ring system. A similar reaction with Ag(NO₃) yields a trimetallic complex [Ag₃{μ-CH₂[CH(pz)₂]₂}₂](NO₃)₃(CH₃CN)₂ (2) that crystallizes from acetonitrile as 2·CH₃CN. Both 1 and 2 form supramolecular structures dominated by cooperative π–π stacking/CH–π hydrogen bonding interactions that we term the ‘quadruple pyrazolyl embrace.’ A Cambridge Structural Database search showed that this interaction is relatively common for metal complexes of simple poly(pyrazolyl)-methane or -borate ligands and occurs in a quarter of all cases.