Crosslinking of the Pd(acacCN)2 building unit with Ag(i) salts: dynamic 1D polymers and an extended 3D network

Abstract

After deprotonation, the acetylacetonate moiety of the ditopic ligand 3-cyanoacetylacetone (HacacCN) acts as a chelating ligand towards Pd(II). The resulting square-planar complex Pd(acacCN)₂ represents a suitable building unit for extended structures via coordination of Ag(I) cations to the peripheral nitrile groups. These target compounds have been structurally characterized: with silver salts of the anions BF₄⁻, ClO₄⁻, PF₆⁻ and CF₃SO₃⁻, chain polymers with an alternating sequence of Pd(II) and Ag(I) are obtained. Solvent molecules and counter anions fill voids close to the silver cations; more weakly coordinating anions are engaged in longer, the triflate anion in a shorter interaction to Ag(I). In contrast to powder samples, larger crystals of these one-dimensional polymers are rather stable with respect to desolvation. Two isomorphous 1D structures undergo a fully reversible k₂ phase transition which can be monitored by single crystal diffraction. The phase transition temperature depends on the nature of the counter anion and may therefore be tuned as a function of chemical composition. The formation of chain polymers by linking Pd(acacCN)₂ building blocks with Ag(I) salts of BF₄⁻, ClO₄⁻, PF₆⁻ and CF₃SO₃⁻ follows chemical intuition whereas its reaction with silver nitrate leads to an unexpected and close-packed 3D structure in which layers of composition Ag(NO₃) are connected by Pd(acacCN)₂ linkers.