Crystal Structure, Absorption, and Fluorescence Spectra of Lanthanoid Glutamate Perchlorate Nonahydrates, Ln2(C5H8NO4)2(ClO4)4.9H2O.

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Abstract
Crystals with the composition Ln2(L-Glu)2(ClO4)4.cntdot.9H2O (Ln = Nd3+, Eu3+, Dy3+ and Ho3+) have been studied. The structures of the complexes with Ho3+ and Dy3+, respectively, have been determined by X-ray diffraction. The unit cell dimensions of the monoclinic crystals were a = 10.863(3), b = 16.587(7), c = 19.741(5) .ANG. and .beta. = 102.93(3).degree. measured at 140 K for the holmium compound, and a = 11.015(1), b = 16.560(2), c = 19.939(3) .ANG. and .beta. = 103.16(1).degree., determined at room temperature for the dysprosium complex. These two structures are isomorphous (P21, Z = 4). The two lanthanoid ions in each complex are bridged by four carboxylate groups so that two of the oxygens are coordinated to both cations. The coordination is completed by four water oxygens around each cation, making the coordination number equal to nine. The L-glutamic acid residues link together the lanthanoid ion pairs into infinite layers. In the voids of this matrix are located the perchlorate groups, exhibiting rotational disorder. The structural models have been refined to linear R values of 0.0515 (for 8974 reflections collected at 140 K for the holmium compound) and 0.0507 (for 7518 reflections measured at room temperature for the dysprosium complex). The absolute configuration of the glutamic acid residues are also confirmed by statistical tests. An absorption spectrum along the crystallographic c axis of a single crystal of the dysprosium complex was recorded at room temperature, and the probabilities of the f-f transitions have been analyzed on the basis of the Judd-Ofelt theory. Solid-state fluorescence spectra of the Nd3+, Eu3+ and Dy3+ compounds have been recorded at 77 K; the results are discussed and Stark components are determined. The decay time for the dysprosium-containing crystal was measured and the fluorescence quenching mechanism is briefly discussed.

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