A tetranuclear oxomolybdenum(V) complex with bridging squarate ligands, ½Mo V 4 O 8 ðOHÞ 2 ðH 2 OÞ 2 ðC 4 O 4 Þ 2  2 Laurent Lisnard, Pierre Mialane, Anne Dolbecq * ,J er^ ome Marrot, Francis S echeresse Institut Lavoisier, IREM, UMR C 0173, Universit e de Versailles Saint-Quentin, 45 Avenue des Etats-Unis, 78035 Versailles, France Received 7 November 2002; accepted 27 December 2002 Abstract The new tetranuclear polyoxomolybdate(V) ion ½Mo V 4 O 8 ðOHÞ 2 ðH 2 OÞ 2 ðC 4 O 4 Þ 2  2 has been obtained in one step by the reaction of sodium molybdate, hydrazine and squaric acid in water and crystallized as a potassium salt. The structure has been solved by single-crystal X-ray diffraction showing the location of the hydroxo and water molecule ligands. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Polyoxometalate; Squarate ligands; Crystal structure; Molybdenum 1. Introduction Polyoxometalates are known for over 150 years, they are often considered as soluble metal oxides and are thus described as fragments of solid lattice structures [1], their applications ranging from catalysis to medical applications [2]. Organic derivatives of polyoxometa- lates [2,3] have been extensively studied for the last two decades as models for the interaction between organic substrates and catalytic metal oxide surfaces and also because they can be used as precursors for the design of extended frameworks, either by the covalent linkage of two anions via a multidentate organic ligand [4] or by the intermediate of transition metal or rare earth ions coordinated to the organic ligand. Organic ligands may also stabilize otherwise unstable species. We have first investigated the coordination chemistry of isopolymo- lybdates(V) with the oxalate ligand. A dinuclear build- ing block ½Mo 2 O 4 ðC 2 O 4 Þ 2 ðH 2 OÞ 2  2 has been isolated by reaction of the dinuclear fragment ½Mo V 2 O 4  2þ in aqueous solution with oxalate ions and its reactivity towards rare earth ions has been studied showing a partial decomposition of the precursor due to the high affinity of the rare earth ions for oxalate ligands [5]. In continuation with this work we have decided to inves- tigate the coordination chemistry of the squarate ligand C 4 O 2 4 . We thus present here the synthesis and struc- tural characterization of a novel tetranuclear complex ½Mo V 4 O 8 ðOHÞ 2 ðH 2 OÞ 2 ðC 4 O 4 Þ 2  2 with two bridging squarate ligands, a water soluble precursor for the construction of extended molecular frameworks. 2. Experimental 2.1. Preparation of K 2 [Mo 4 O 8 (OH) 2 (H 2 O) 2 (C 4 O 4 ) 2 ] 5H 2 O Na 2 MoO 4  2H 2 O (0.50 g, 2 mmol) was dissolved in 5 mL of 4 M HCl, and N 2 H 4  H 2 O (0.025 mL, 0.5 mmol) was added. The mixture was stirred for 1 h at 65 °C. The resulting dark red solution was then allowed to cool at room temperature and a solution of H 2 C 4 O 4 (0.114 g, 1 mmol) in 5 mL of water was added. The pH was ad- justed to 2 by a dropwise addition of a 2 M LiOH so- lution. The solution was stirred overnight. The orange precipitate (0.365 g, yield 81% based on Mo), a mixed Li and Na salt of formula LiNa½Mo 4 O 8 ðOHÞ 2 ðH 2 OÞ 2 ðC 4 O 4 Þ 2  2H 2 O, was then filtered and washed with EtOH and dried with Et 2 O. Anal. calc. for H 10 C 8 LiNaMo 4 O 22 : Li, 0.80; Mo, 44.31; Na, 2.66. Found: Li, 0.67; Mo, 44.59; Na, 2.07. The mixed Li and Na salt Inorganic Chemistry Communications 6 (2003) 503–505 www.elsevier.com/locate/inoche * Corresponding author. Tel.: +33-1-39-25-43-83; fax: +33-1-39-25- 43-81. E-mail address: dolbecq@chimie.uvsq.fr (A. Dolbecq). 1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1387-7003(03)00028-5