Structural Study Of Mixed Crystals Of [Zn1-Xrux(Bpy)(3)][Nacr(Ox)(3)] Probed By High-Resolution Absorption Spectroscopy And High-Pressure Experiments

In the mixed crystal series of the cubic three-dimensional networks of composition [Zn1-x,Ru-x(bpy)(3])[NaCr(ox)(3)] (0 <= x <= 1, ox = C2O42-, bpy = 2,2'-bipyridine), high-resolution absorption spectroscopy in the region of the (4)A(2)-> E-2 transition (R-lines) reveals the creation of five specific spectroscopic sites for the [Cr(ox)(3)](3-) complex. The concentration of these spectroscopic sites follows a binomial distribution of [Zn(bpy)(3)](2+) and [Ru(bpy)(3)](2+) among the four nearest neighbors of a given [Cr(ox)3]3 complex within the network. The tris-bipyridine complexes occupying those positions have an optimal pi-pi interaction with the oxalate ligands of the tris-oxalate chromophore. The energy of each spectroscopic ICr(ox)(3)](3-) site depends on the total concentration of [Ru(bpy)(3)](2+) in the mixed crystal and on its specific distribution among the four nearest neighbors. Single crystal X-ray diffraction indicates a reduction of the unit cell volume when [Zn(bpy)(3)](2+) (a = 15.6365(18) angstrom) is substituted by [Ru(bpy)(3)](2+)(a= 15.5098(6) angstrom). This alone would lead to a red-shift of the R lines in analogy to the red-shift of 25.2 cm(-1)/GPa due to the decrease of the metal ligand Cr-O bond length as observed in high-pressure luminescence experiments. However, specific pi-pi interactions with the nearest neighbors have the opposite effect and shift the transition in discrete jumps to higher energies with increasing [Ru(bpy)(3)[(2+) mole fraction.