After deprotonation, the acetylacetonate moiety of the ditopic ligand 3-cyanoacetylacetone (HacacCN) acts as a chelating ligand towards PdIJII). The resulting square-planar complex PdIJacacCN) 2 represents a suitable building unit for extended structures via coordination of AgIJI) cations to the peripheral nitrile groups. These target compounds have been structurally characterized: with silver salts of the anions BF 4 − , ClO 4 − , PF 6 − and CF 3 SO 3 − , chain polymers with an alternating sequence of PdIJII) and AgIJI) 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 AgIJI). 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 k 2 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 PdIJacacCN) 2 building blocks with AgIJI) salts of BF 4 − , ClO 4 − , PF 6 − and CF 3 SO 3 − follows chemical intuition whereas its reaction with silver nitrate leads to an unexpected and close-packed 3D structure in which layers of composition AgIJNO 3 ) are connected by PdIJacacCN) 2 linkers. CrystEngComm This journal is ; Tel: +1 612 8021080† Electronic supplementary information (ESI) available: Crystallographic information in CIF format, displacement ellipsoid plots for 1-7, powder patterns for 2, 3, 5 and 7, intensity ratio IIJ f/t) for 2 and 3 over larger temperature ranges, intensity of single reflections in 2, 3 and 4, 19 F NMR result of 4 and sequence of slides visualizing the phase transition in 2.