Polyhedron 18 (1999) 2781–2785 www.elsevier.nl / locate / poly Synthesis and structure of two molybdovanadates containing coordinatively bound oxalato ligands: (NH ) [Mo V O (C O ) ]?6H O and 4 6 6 2 24 2 4 2 2 (NH ) [H Mo VO (C O ) ]?2H O 4 4 2 2 2 12 2 4 2 2 * ´ Marina Cindric, Neven Strukan, Boris Kamenar Laboratory of General and Inorganic Chemistry, Chemistry Department, Faculty of Science, University of Zagreb, POB 153, HR-10001 Zagreb, Croatia Received 9 March 1999; accepted 15 June 1999 Abstract The compounds (NH ) [Mo V O (C O ) ]?6H O ( I) and (NH ) [H Mo VO (C O ) ]?2H O (II) have been prepared from 4 6 6 2 24 2 4 2 2 4 4 2 2 2 12 2 4 2 2 molybdenum(VI) oxide and ammonium vanadate in aqueous solution through the addition of ammonium oxalate, and their structures 62 determined by X-ray structure analysis. Whereas the molybdovanadate anion [Mo V O (C O ) ] found in (I) consists of six MoO 6 2 24 2 4 2 6 42 42 and two VO edge-sharing octahedra of the g-[Mo O ] type structure, the tetranuclear anion [H Mo V O (C O ) ] of (II) adopts 6 8 26 2 2 2 12 2 4 2 the structure with a M O core. Both complexes contain bidentate oxalato ligands bonded to the vanadium ions. In both crystal structures 4 16 the molybdovanadate anions are mutually hydrogen bonded by ammonium ions and water molecules.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Molybdovanadates; Oxalato ligand; Crystal structure determination 1. Introduction V) coordinated by organic ligands are still rare and up to now only a few examples are described in the literature The surfaces of many polyoxoanions mimic those of [14,15]. heterogeneous metal oxides so that it may be expected that It has been established that although many different further insights into heterogeneous catalysis by oxides as species of polyoxometalates exist in aqueous solution, their well as the development of new types of catalysts will formation strongly depends upon the metal ions con- result from a study of organic derivatives of polyoxoanions centration, the range of pH and the temperature [10]. From 22 [1–10]. The first such polyanions [(R AsO )Mo O H] such solutions, crystals of different composition appear 2 2 4 13 containing covalently bonded organic groups were reported because of their insolubility rather than because of the by A. Rosenheim and A. Bilecki in 1913 [11]. In the last relative stability of the species in solution [16]. ten or more years several polyoxometalates, in particular As part of our research into polyoxoanions coordinated polyoxomolybdates, containing oxygen- or nitrogen-donat- by carboxylato ligands [12,13], in this paper we describe ing ligands have been prepared and structurally character- the synthesis and crystal structure of ized [10,12,13]. However, polyoxoanions of the type (NH ) [Mo V O (C O ) ]?6H O ( I) and 4 6 6 2 24 2 4 2 2 n 2 [M M O L ] with mixed metals (e.g. M5Mo and M95 (NH ) [H Mo VO (C O ) ]?2H O ( II) as two new x y z o 4 4 2 2 2 12 2 4 2 2 examples of molybdovanadates coordinated by oxalato ligands. Both complexes resulted from the same reaction *Corresponding author. Tel.: 1385-1-4606-672; fax: 1385-1-4611- of molybdenum(VI) and vanadium(V) oxides and am- 191. E-mail address: bkamenar@chem.pmf.hr (B. Kamenar) monium oxalate. However, while the former is a typical 0277-5387 / 99 / $ – see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0277-5387(99)00184-9