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

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{mu-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{mu-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 – stacking/CH– 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.