Counterion effect on the formation of coordination polymer networks between AgNO3 and L (2,2 '-oxybis(ethane-2,1-diyl) diisonicotinate). Part 2

Herein we report the synthesis and characterization by single crystal X-ray diffraction of three new silver(I) complexes {[Ag-2 center dot L-2](NO3)(2)(H2O)(4)} (1), {[Ag-2 center dot L-2](NO3)(2)} (2) and {[Ag-2 center dot L-2](NO3)(2)} (3). Whereas compounds 2 and 3 are polymorphs, compound 1 crystallizes as the pseudo-polymorphic form of 2 and 3. These compounds were obtained from the reaction of silver nitrate with the flexible ligand 2,2'-oxybis(ethane-2,1-diyl) diisonicotinate (L). The main structural motifs for complexes 1-3 are zero-dimensional metallacycles, in which two silver(I) cations are coordinated by two ligands L and their counterions. As a result of its unpredictable coordinating ability, the nitrate anion coordinates the Ag(I) cation in a mu(1)mu(2)-fashion in complex 1, in 2 it is coordinated in an asymmetrical mu(2)-mode, and in 3 the anion is strongly mu(2)-symmetrical coordinating. The coordination of the NO3- counterions to the metal cation affects the overall supramolecular interactions in the crystalline state of the complexes (e.g. Ag(I)center dot center dot center dot Ag(I), pi center dot center dot center dot pi, hydrogen bonds and C-H center dot center dot center dot pi interactions). These interactions determine the physical properties of these compounds. On heating, the crystals of compound 3 are irreversibly transformed into compound 2. The conversion is supported by the change in the coordination mode of the nitrate counterion toward the Ag(I) cation. The solubility dependence of AgNO3 in the different organic solvents used for the reactions may determine the structural diversity in the supramolecular architecture for these complexes.