Electronic energy transfer from [Cr(ox)3]3- (ox = oxalate) in three-dimensional (3D) anionic oxalate networks to encapsulated [Cr(bpy)3]3+ (bpy = 2,2‘-bipyridine) cations at 1.5 K was investigated by time-resolved luminescence spectroscopy. Two series of mixed crystals of nominal compositions [NaAl1 - x Cr x (ox)3][Rh0.99Cr0.01(bpy)3]ClO4 (x = 0, 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, and 1) and [NaAl0.99Cr0.01(ox)3][Rh1 - y Cr y (bpy)3]ClO4 (y = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) were utilized. Energy transfer from [Cr(ox)3]3- to [Cr(bpy)3]3+ occurs by two mechanisms. Rapid, short-range transfer (k et > 106 s-1) is attributed to superexchange coupling between the Cr3+ ions via π overlap of the oxalate and bipyridine ligands. In addition, at low [Cr(ox)3]3- concentrations (nominally x = 0.01) a very much slower process with a maximum k et ≈ 200 s-1 is identified in the time-resolved spectra and attributed to a dipole−dipole mechanism. Furthermore, the resonant [Cr(ox)3]3- to [Cr(ox)3]3- energy migration previously reported by von Arx et al. (Phys. Rev. (1996), B54, 15800) assists [Cr(ox)3]3- to [Cr(bpy)3]3+ transfer as the [Cr(ox)3]3- concentration increases.

Based on a synthetic strategy, extended anionic, homo and bimetallic oxalato-bridged transition-metal compounds with two (2D) and three-dimensional (3D) connectivities can be synthesized and crystallized. Thereby, the choice of the templating counterions will determine the crystal chemistry. Since the oxalato bridge is a mediator for both antiferro and ferromagnetic interactions between similar and dissimilar metal ions, long-range magnetic ordering will occur. Examples of the determination of magnetic structures in 2D and 3D compounds by means of elastic neutron scattering methods will be discussed. In addition, due to the possibility of the variation of different metal ions in varying oxidation states, interesting photophysical processes can be observed within the extended three-dimensional host/guest systems

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