The emission spectra of Sm2+Â doped in BaFBr and SrFBr hosts were measured at 10Â K from ambient pressure to 8Â GPa. The crystal field energy levels determined from the emission spectra were used to extract the free ion parameters (FkÂ andÂ Î¶Â ) and crystal field parameters (Bqk). The variation ofÂ FkÂ andÂ Î¶Â as a function of pressure was studied systematically and was discussed in relation to the central field and symmetry restricted covalency models. The change of the spin orbit coupling parameter (Î¶) with pressure for SrFBr:Sm2+Â showed very different behavior than in other matlockite hosts. Moreover the variation ofÂ BqkÂ under pressure was studied. The pressure dependence of theÂ BqkÂ was described quantitatively using the Superposition Model (SM) with the help of structural parameters as a function of pressure, obtained from periodic DFT calculations. The validity of the SM was tested for Sm2+Â in BaFBr and SrFBr. It is shown that this model does not apply to SrFBr, in contrast to other matlockite host materials.
The structure and thermodynamic properties of lanthanide complexes with a new tripodal ligandÂ L2Â have been elucidated using different physicochemical methods. At stoichiometric ratios, the tetrahedral three-dimensional complexes with lanthanide cations are formed in acetonitrile with good stabilities. Despite minor structural changes comparing to previously investigated tripodal ligands, the resulting assembly exhibits different features revealed with the crystal structure of [Eu4L24](OH)(ClO4)11Â (orthorhombic,Â Pbcn). Interestingly, the highly charged edifice contains an inner cage encapsulating a perchlorate anion. Such lanthanide mediated cage-like assemblies are rare, and may be of interest for different sensing applications. Indeed, the anionic guest can be exchanged with different anions. The related hostâ€“guest equilibria were investigated with NMR techniques. Various aspects of these reactions are qualitatively discussed.
Resonant excitation energy transfer from [Cr(ox)3]3- to [Cr(bpy)3]3+ in the doped 3D oxalate networks [Rh1-xCrx(bpy)3][NaMIII1-yCry(ox)3]ClO4 (ox=C2O4-, bpy=2,2â€™-bipyridine, M=Al,Rh) is due to two types of interaction, namely super exchange coupling and electric dipoleâ€“dipole interaction. The energy transfer probability for both mechanisms is proportional to the spectral overlap of the 2Eâ†’4A2 emission of the [Cr(ox)3]3- donor and the 4A2â†’2T1 absorption of the [Cr(bpy)3]3+ acceptor.The spin-flip transitions of (pseudo-)octahedral Cr3+ are known to shift to lower energy with increasing pressure. Because the shift rates of the two transitions in question differ, the spectral overlap between the donor emission and the acceptor absorption is a function of applied pressure. For [Rh1-xCrx(bpy)3][Na-M1-yCry(ox)3]ClO4 the spectral overlap is thus substantially reduced on increasing pressure from 0 to 2.5 GPa. As a result, the energy transfer probability decreases with increasing pressure as evidenced by a decrease in the relative emission intensity from the [Cr(bpy)3]3+ acceptor.
In the mixed crystal series of the cubic three-dimensional networks of composition [Zn1âˆ’xRux(bpy)3][NaCr(ox)3] (0 â‰¤ x â‰¤1, ox = C2O42âˆ’, bpy = 2,2â€²-bipyridine), high-resolution absorption spectroscopy in the region of the 4A2â†’2E transition (R-lines) reveals the creation of five specific spectroscopic sites for the [Cr(ox)3]3âˆ’ 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]3âˆ’ complex within the network. The tris-bipyridine complexes occupying those positions have an optimal Ï€âˆ’Ï€ interaction with the oxalate ligands of the tris-oxalate chromophore. The energy of each spectroscopic [Cr(ox)3]3âˆ’ 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) Ã…) is substituted by [Ru(bpy)3]2+ (a = 15.5098(6) Ã…). This alone would lead to a red-shift of the R lines in analogy to the red-shift of 25.2 cmâˆ’1/GPa due to the decrease of the metal ligand Crâˆ’O bond length as observed in high-pressure luminescence experiments. However, specific Ï€âˆ’Ï€ 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.