b -Xenophyllite-type Na 4 Li 0.62 Co 5.67 Al 0.71 (AsO 4 ) 6 Riadh Marzouki, Wafa Frigui, Abderrahmen Guesmi, Mohamed Faouzi Zid* and Ahmed Driss Laboratoire de Mate ´riaux et Cristallochimie, Faculte ´ des Sciences de Tunis, Universite ´ de Tunis ElManar, 2092 Manar II Tunis, Tunisia Correspondence e-mail: faouzi.zid@fst.rnu.tn Received 2 September 2013; accepted 11 September 2013 Key indicators: single-crystal X-ray study; T = 298 K; mean (As–O) = 0.004 A ˚ ; disorder in main residue; R factor = 0.026; wR factor = 0.068; data-to-parameter ratio = 10.0. The title compound, tetrasodium lithium cobalt aluminium hexa(orthoarsenate), was synthesized by a solid state reaction route. In the crystal structure, Co 2+ ions are partially substituted by Al 3+ in an octahedral environment [M1 with site symmetry 2/m; occupancy ratio Co:Al = 0.286 (10): 0.714 (10)]. The charge compensation is ensured by Li + cations sharing a tetrahedral site with Co 2+ ions [M2 with site symmetry 2; occupancy ratio Co:Li = 0.690 (5):0.310 (5)]. The anionic unit is formed by two octahedra and three tetrahedra linked only by corners. The CoM1M2As 2 O 19 units associate to an open three-dimensional framework containing tunnels propagating along the a-axis direction. One Na + cation is located in the periphery of the tunnels while the other two are situated in the centres: all Na + cations exhibit half- occupancy. The structure of the studied material is compared with those of various related minerals reported in the literature. Related literature For applications of these and related phases, see: Aurivillius et al. (1964); Nagpure et al. (2010); Prabaharan et al. (1997). For details of structurally related compounds, see: Alvarez-Vega et al. (2006); Keller et al. (1981); Frigui et al. (2012); Goodenough et al. (1976); Marzouki et al. (2012); Ben Smida et al. (2013); Guesmi & Driss (2012); Moring & Kostiner (1986); Kobashi et al. (1998); Ben Smail et al. (1999); Burke et al. (2006); Redhammer et al. (2005); Hatert et al. (2005); Moore & Molin- Case (1974). For the bond-valence method, see: Brown & Altermatt, (1985). Experimental Crystal data Na 4 Li 0.62 Co 5.67 Al 0.71 (AsO 4 ) 6 M r = 1283.06 Monoclinic, C2=m a = 10.7444 (9) A ˚ b = 14.847 (2) A ˚ c = 6.7223 (8) A ˚  = 105.51 (2)  V = 1033.3 (2) A ˚ 3 Z =2 Mo K radiation  = 14.22 mm 1 T = 298 K 0.26  0.24  0.22 mm Data collection Enraf–Nonius CAD-4 diffractometer Absorption correction:  scan (North et al., 1968) T min = 0.033, T max = 0.042 1615 measured reflections 1174 independent reflections 1048 reflections with I >2(I) R int = 0.027 2 standard reflections every 120 min intensity decay: 1.4% Refinement R[F 2 >2(F 2 )] = 0.026 wR(F 2 ) = 0.068 S = 1.13 1174 reflections 117 parameters 2 restraints Á max = 0.87 e A ˚ 3 Á min = 0.87 e A ˚ 3 Data collection: CAD-4 EXPRESS (Duisenberg,1992; Macı´c ˇek & Yordanov, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve struc- ture: SHELXS97 (Sheldrick, 2008); program(s) used to refine struc- ture: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publi- cation: WinGX (Farrugia, 2012). 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E69, i65–i66 doi:10.1107/S1600536813025233 Marzouki et al. i65 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368