| Autor: |
Nimoh H; Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany.; UCCS (Unité de Catalyse et Chimie du Solide), Université de Lille, Centrale Lille/ENSCL, 59000 Lille, France., Mentré O; UCCS (Unité de Catalyse et Chimie du Solide), Université de Lille, Centrale Lille/ENSCL, 59000 Lille, France., Hammer EM; Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany., Jähnig M; Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany., Dittrich V; Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany., Minaud C; UCCS (Unité de Catalyse et Chimie du Solide), Université de Lille, Centrale Lille/ENSCL, 59000 Lille, France., Colin CV; Univ. Grenoble Alpes, CNRS, Institut Néel, 38000 Grenoble, France., Arevalo-Lopéz A; UCCS (Unité de Catalyse et Chimie du Solide), Université de Lille, Centrale Lille/ENSCL, 59000 Lille, France., Glaum R; Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany. |
| Abstrakt: |
Blue/turquoise crystals of Sr 2 Cr II (PO 4 ) 2 with prismatic shape and edge-length of up to 1 mm were obtained by a vapor-phase moderated solid-state reaction at 1273 K in sealed silica tubes. Its crystal structure was solved and refined from a triply twinned ("trilling") crystal [ Pbca (no. 61), Z = 12, a = 10.7064(6) Å, b = 9.2730(5) Å, c = 21.2720(7) Å, R 1 = 0.038]. Sr 2 Cr(PO 4 ) 2 belongs to the small family of inorganic solids containing divalent chromium, where the rare Cr 2+ ions are stabilized by the inductive effect of the phosphate groups. As expected from its d 4 ( S = 2) electronic configuration, the Jahn-Teller effect (JT) is prominent, leading for the two independent Cr 2+ ions to square-pyramidal Cr(1)O 4+1 and square-planar Cr(2)O 4 coordination within a 3D chromium phosphate network [Cr II 2 (PO 4 ) 4 ] 8 . Topologically, the Cr(1) and Cr(2) cations are arranged in separate alternating layers stacked along the c axis. In their respective layers, Cr(1) shows a gapped 2D topology and only weak interaction with the adjacent Cr(2) layers. However, below T N1 ∼11.3 K, Cr(1) orders antiferromagnetically into a noncollinear structure, leaving nearly paramagnetic Cr(2) idle spins, strongly frustrated by the Cr(1) moments of the next layers. On further cooling, below T N2 ∼3.6 K, the ordering of Cr(2) occurs via an additional magnetic irreducible representation, which splits the Cr(1) into Cr(1)a and Cr(1)b orbits, thus lifting the frustration on Cr(2). The corresponding P2 1 ca.29.99 magnetic space group forces a crystal symmetry lowering, plausibly signed by a change of the magnetostrictive coefficient from positive to negative below T N2 . The optical transitions observed for the JT d 4 ions are in good agreement with our crystal picture from the DFT calculations. A detailed analysis within the angular overlap model explains the surprisingly different d orbital splitting by the ligand field for the chromophores Cr(1)O 4+1 and Cr(2)O 4 . |
