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The title compound has been synthesized and its structure has been solved at room temperature. It crystallizes in the tetragonal system, space group P42/m«m. Its lattice constants are a = b = 9.50 ± 0.02 Á and c = 13.94 ± 0.03 Á with Z = 2. The structure consists of [Cu2(tmen)2(N3)(OH)]2+ dinuclear cations and perchlorate anions. In each cationic unit, the copper(II) ions are four-coordinated with planar surroundings; they are bridged by an azido group in an end-on fashion and by a hydroxo group. The bridging network is disordered. The Cu-NPl distance is 1.960 (9) Á, and the Cu-NPl-Cu angle is 99.4 (6)°, NPl being the N0,5O0,5 composite bridging atom. The magnetic properties of the title compound have been investigated in the 2-300 K temperature range. T, the product of the molar magnetic susceptibility and the temperature, is equal to 1.02 cm3 mol'1 K at 295 K, increases up to 1.15 ± 0.02 cm3 mol'1 K at 150 K, and then remains constant down to 20 K. This behavior shows that the ground state is the spin triplet and that the excited spin singlet state is so high in energy that it is only weakly populated, even at room temperature. This singlet-triplet energy gap is estimated to be larger than 200 cm'1. The specific ability of the end-on azido bridge to favor the triplet state in dinuclear copper(II) complexes is emphasized. An interpretation based on a spin polarization effect is proposed. The magnetic properties of the title compound are compared to those of [Cu(tmen)(N3)2]2, where the two copper(II) ions are noncoupled.

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The Raman spectrum of a single crystal of monoclinic B-type (C$, ) gadolinium sesquioxide is presented. The low temperature polarization studies allowed the unambiguous attribution of 20 among the 21 normal modes expected according to the C,, factor group analysis predictions. IYTRODUCTIONThe lanthanide sesquioxides are known to crystallize in various structures according to the radius of the rareearth ion. An investigation of these different crystallographic types was undertaken by Raman spectroscopy. The interpretation of the Raman spectra of the hexagonal A-type (Did, P 3 m l ) oxides La203, Pr203, Nd203 has already been published.' The study of the monoclinic B-type (C;,, C 2 / m ) oxides Sm2O3, Eu203, Gd203 is now in progress, in order to establish correlations between Raman spectra and crystallographic data for these two structures.The purpose of the present paper is the interpretation of the Raman spectrum of monoclinic B-type Gd2O3 single crystals. Previous reports on the vibrational spectra of GdzO3 dealt with the IR spectra of the cubic (C-type structure) oxide.'-' No earlier Raman data on the B-type rare-earth sesquioxide structures are known to the authors. EXPERIMENTALSingle crystals of Gd203 were grown by the flame fusion method (Verneuil process) described elsewhere.' The starting material was the sesquioxide powder. The crystals obtained were rods of 5 mm diameter and 20 mm length but in fact were made of two or three large single crystals with nearly the same orientation. They were transparent and colourless: The single crystals were easily cleaved along the (201) planes. The samples were thin platelets ( 4 x 2~ 1 mm3): the largest face was a cleavage plane parallel to the c2 axis direction, the other two faces were cut (one parallel and one perpendicular to the c2 axis direction) and polished.The room temperature spectra were obtained on a Jobin-Yvon HG 2 s spectrometer equipped with a Spectra-Physics ionized argon laser (4 W). Some spectra showed sharp fluorescence bands which were identified either by comparison with the anti-Stokes spectra or by varying the excitation frequency.The low temperature spectra (from room temperature to 5 K) were recorded on a Coderg T800 spectrometer using the 514.5 nm line of a Spectra-Physics ionized argon laser (15 W). The crystal was cooled in a conventional cryostat with a dynamic helium flow.