Vibronic spectra and details of the structure of europium nitrates with derivatives of 1,10-phenanthroline

Luminescence and excitation of luminescence vibronic spectra as well as IR and Raman spectra of europium nitrates with 1,10-phenanthroline derivatives of formula Eu(NO3)(3).Ph-2 were studied. The effect of size of ligands and their effective charges on crystal structure and, as a consequence, on spe ctroscopic characteristics was investigated under conditions where one type of ligand (NO3- group) is sufficiently rigid. The second ligand, heterocyc lic diimine, can change its size and donor-acceptor properties when the sub stituents are varied. Stark splittings and relative intensities of the Eu3 electronic transitions, the behaviour of vibration frequencies, and vibron ic interaction were studied. It was demonstrated that nitrates under invest igation have identical composition but form two different structural groups with small and bulky phenanthroline derivatives due to the influence of st eric factor. All nitrate anions in the compounds are coordinated and the Eu -O (NO3-) bonds are relatively strong. The values of the splitting of stret ching vibrations of the NO3--anions (Delta=nu(4)-nu(1)) and position of the band of nu(Eu-O) vibration show that the strongest Eu-O bonds are formed i n Eu(NO3)(3).Nphen(2), Eu(NO3)(3).Tmphen, and Eu(NO3)(3).Dphphen, due to hi gh acceptor properties of nitro-phenanthroline and large size of tetramethy l- and diphenyl-phenanthroline molecules. Weak vibronic mixing of electroni c and vibronic states was demonstrated in the region of D-5(0)-F-7(2) trans ition of Eu3+. The vibronic satellites of D-5(0)-F-7(0) -transition due to vibrations of the NO3--group borrow about 1-2% of the intensity of the elec tric-dipole D-5(0)-F-7(2) transition yielding the increase of their relativ e intensity of 100 times in the Stokes sideband. (C) 2000 Elsevier Science S.A. All rights reserved.