SHORT COMMUNICATION A Nonanuclear Ni II Cluster with a 1,2,4-Triazolo[4,3-a]pyrimidine Derivative Sawsan Salameh, [a] Mohammad Abul-Haj, [a] Miguel Quirós,* [b] and Juan M. Salas [b] Keywords: Cluster compounds / Nickel / Triazolopyrimidine / Magnetic properties This article describes the nickel cluster compound [Ni 9 - L 8 (OH) 6 (NH 3 ) 4 (H 2 O) 8 ](NO 3 ) 4 ·8H 2 O, where L represents the anionic form of the ligand 7,8-dihydro-1,2,4-triazolo[4,3-a]- pyrimidin-7-one. The structure of the cation of this com- pound is rather complicated, involving nine metal atoms, eight bridging organic ligands, bridging hydroxyl groups, and terminal ammonia and water molecules. The central nickel atom lies on a crystallographic inversion centre, while the other eight define two disorted “cubane-like” [Ni 4 - Introduction The condensation of a 1,2,4-triazole ring and another of a pyrimidine molecule may give rise to four different fami- lies of heterocyclic, bicyclic compounds. Among these, the thermodynamically more stable, and hence the most studied ones, are 1,2,4-triazolo[1,5-a]pyrimidines, which bind to metal atoms in a number of different ways to give rise to different structural motifs. [1] More bonding possibilities arise if the positions of the nitrogen atoms in the heterocy- cle are interchanged, defining the isomeric families 1,2,4- triazolo[1,5-c]pyrimidines, [2] 1,2,4-triazolo[4,3-a]pyrimi- dines, [3] and 1,2,4-triazolo[4,3-c]pyrimidines. [4] These are far less thermodynamically stable, and isomerisation processes (Dimroth rearrangement) are possible on heating, possibly catalysed by acidic or basic pH conditions, [5] so working with any of these families is potentially more difficult. Our research group has just started to explore the coordi- nation possibilities of one of these families, namely the 1,2,4-triazolo[4,3-a]pyrimidines, which differ from the 1,5-a derivatives in the position of one of the nitrogen atoms of the triazole ring, which is separated as far as possible from the pyrimidine ring, is subject to less steric hindrance, and is contiguous to the other external imidazole nitrogen atom. The skeleton of this family of compounds, as well as the numbering scheme used for identifying their atoms, is shown in Scheme 1. [a] Department of Chemistry and Chemical Technology, Al-Quds University, P. O. Box 20002 Abu Dis, Jerusalem, Palestine [b] Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain Fax: +34-958-248526 E-mail: mquiros@ugr.es Eur. J. Inorg. Chem. 2005, 2779–2782 DOI: 10.1002/ejic.200500208 © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2779 (OH) 3 ] 5+ subclusters. Each subcluster is linked to the central atom by three triple bridging organic ligands. Additional L ligands bridge two external metal atoms in each subcluster. The variation with temperature of the magnetic susceptibility of the compound indicates the presence of both ferromag- netic and antiferromagnetic interactions; the latter is pre- dominant. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) Scheme 1. The first metal complex of one of these derivatives (with an exocyclic oxo group in position 7) is a silver dimer re- cently published by us. [6] In this complex the ligand bridges the metal atoms through the two nitrogen atoms of the tri- azole ring. Following this research line, we have started to explore the behaviour of this ligand towards metal atoms of the first transition series. We used a pH high enough to deprotonate the nitrogen atom of the pyrimidine ring, which usually carries the acidic proton (N8), so that it could become a new binding site, and we have been successful in obtaining a crystalline solid with nickel() in ammonia aqueous solution. The solid is a nonanuclear cluster, and the metal atoms are bridged by organic ligands and hy- droxyl groups, which transmit both ferromagnetic and anti- ferromagnetic interactions. Results and Discussion The main feature of the crystal structure of the title com- pound is the presence of centrosymmetric clusters built from nine nickel atoms, eight L ligands, six hydroxo groups, four ammonia molecules and eight water molecules. Dis- crete clusters with nine metal atoms are not very frequently observed, nevertheless, a number of nonanuclear nickel compounds have been described with different bridging li-