Self-assembly in tetrameric 1:1 silver(I) halide:tri-p-tolylphosphine complexes: An in-depth structural investigation Gertruida J.S. Venter, Andreas Roodt, Reinout Meijboom * ,1 Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa article info Article history: Received 10 June 2008 Received in revised form 4 November 2008 Accepted 7 November 2008 Available online 13 November 2008 Keywords: Silver Phosphine X-ray crystallography Stella quadrangula abstract The reaction of silver(I) bromide with tri(p-tolyl)phosphine in MeCN solution in 1:1 molar ratios resulted in a complexes of the formula [AgBr{P(4-MeC 6 H 4 ) 3 }] 4 . This compound has a tetrameric structure with a concave coordination polyhedron, in between a cube and a stella quadrangula. Weak silver–silver inter- actions were observed. The current compound is compared to the Cl and I analogs using distance–dis- tance plots. The silver–silver interactions seem to dominate the geometry of these tetrameric type of complexes. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The first tertiary phosphine complexes of Ag(I) of the type [AgXL n ](L = tertiary phosphine; n = 1–4; X = coordinating or non- coordinating anion) were prepared in 1937 [1] and are the first crystallographically characterized examples of metal phosphine complexes. Since then, more than a thousand [2] complexes con- taining silver coordinated to phosphorous donor ligands have been synthesized and characterized. In the past it was shown that sil- ver(I) complexes can crystallize in different polymorphic varia- tions, leading to such extreme differences as ‘cubic’ [3] and ‘step’ tetramers, depending on the solvent of crystallization [4]. We re- cently reviewed the structural chemistry of silver(I) complexes with, mainly, phosphine ligands [5] and refer to this review for more information on the various complexes. An interest in the abil- ity of silver(I) complexes to adopt geometries with variable nucle- arities has led to the study of silver(I) complexes with various counterions and different ratios of tri-p-tolylphosphine [6]. Though a number of tetranuclear structures were reported pre- viously, most of them were described to contain a ‘cubic’ geometry. However, for a number of these structures it would be more correct to describe them to contain ‘stella quadrangula’ geometry. This geometry was first discussed in relation to silver complexes in 1985 [7].A stella quadrangular geometry can be described as four tetrahedra sharing common edges, in the current case, tetrahedra formed by the four Ag atoms, the four halide atoms and the four P atoms, as well as an empty tetrahedron. The ratios of AgÁÁÁAg and XÁÁÁX distances, for an ideal stella quadrangula and an ideal cu- bic geometry is 2/3 and 1, respectively [7]. We previously communicated the structure of [AgIP(4- MeC 6 H 4 ) 3 ] 4 [8]. In this paper, the title compound [AgBrP(4- MeC 6 H 4 ) 3 ] 4 , 2, is described and compared to similar tetrahedral [AgXP(4-MeC 6 H 4 ) 3 ] 4 structures, with X = Cl (1) [9] and I (3) [8].A comparison of their geometries is made using RMS overlay calcula- tions and distance–distance plot analysis. 2. Experimental 2.1. Synthesis The title compound was prepared in a similar way to previously published procedures [8]. A heterogeneous mixture of AgBr (0.1913 g, 1.019 mmol) was heated under reflux in a solution of P(4-MeC 6 H 4 ) 3 (0.1570 g, 0.5015 mmol) in acetonitrile until dis- solved. The product was recrystallized from acetone, giving color- less crystals in a yield of 0.0511 g (20.13%). d P{H} (CD 2 Cl 2 , À80 °C, 242.99 MHz): 4.89 (d, J 107 Ag— 31 P 439.84 Hz, d, J 107 Ag— 31 P 468.39 Hz). 2.2. Crystallography and calculations Crystals of 2 were grown from acetone at room temperature. Single crystal X-ray diffraction data for 2 were collected on a Bru- ker X8 Apex II 4K Kappa CCD diffractometer using Mo Ka (0.71073 Å) radiation with u and x-scans at 100(2) K. The initial unit cell and data collection were achieved by the Apex 2 [10] 0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2008.11.004 * Corresponding author. Tel.: +27 11 559 2367; fax: +27 11 559 2819. E-mail address: meijboomr.sci@ufs.ac.za (R. Meijboom). 1 Present address: Department of Chemistry, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa. Inorganica Chimica Acta 362 (2009) 2475–2479 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica