Theoretical Investigation of the Stepwise Hydrolysis of the [Re 3 (μ-Cl) 3 Cl 9 ] 3- Anion Dimitrios G. Liakos, ² Emmanuel D. Simandiras,* ,² Nikolaos Psaroudakis, ‡ and Konstantinos Mertis ‡ Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou AVenue, 11635 Athens, Greece, and Department of Chemistry, Athens UniVersity, 15771 Athens, Greece Received September 28, 2006 A detailed study of the stepwise substitution of the chloride ligands in the [Re 3 (μ-Cl) 3 Cl 9 ] 3- (1) anion by water molecules is presented using theoretical methods. Ligand lability as well as the structure and relative stability of the various mono-[Re 3 (μ-Cl) 3 Cl 8 (H 2 O)] 2- (2a,b) and dihydro-[Re 3 (μ-Cl) 3 Cl 7 (H 2 O) 2 ] - (3a-f) conformers is examined. Clear preferences for the positions of the incoming water ligands are proposed based on calculated energy and vibrational data, which fully agree with the experimental results. Introduction The realization in the early 1960s 1-3 that the polymeric [Re 3 (μ-Cl) 3 Cl 6 ] n halide and its related cluster anion 1 contain a 12e - [Re 3 ] 9+ core, with the metal atoms forming between them three double bonds, 4,5 played a key role in the development of the field of metal-metal bonds and transi- tion-metal clusters. 6 This extremely interesting topic of triangulo and higher nuclearity rhenium halide clusters has been recently reviewed by Walton. 7 Among the wealth of synthetic, crystallographic, and physicochemical studies concerning 1, a notable exception is the scarcity of theoretical studies. Apart from the original SCF-Xa 8 investigations and a previous study by us, 9 no other theoretical work has, to our knowledge, been applied to this cluster; this with certainty may be attributed to the extremely large size of the calculations involved. An interesting aspect in the chemistry of 1 (see Figure 1 for labeling of ligands) is the relative lability of terminal in-plane (equatorial), terminal out-of-plane (axial), and bridging halide ligands in halogen exchange and solvolytic reactions. On the basis of halogen, radiochemical ( 36 Cl - ), and chloride-pseudohalide (N 3 - , CN - , and NCS - ) exchange reactions, this was found to be Cl equatorial > Cl axial . Cl bridging . 10 In a previous work, 9 we examined this from a theoretical point of view and found that ab initio calculations back the experimental findings. 7 Herein, we address to a more detailed extent the solvolysis of Re-Cl bonds by water molecules, and in a thorough study, using density functional theory (DFT), we investigate the intermediate products in the stepwise displacement of the * To whom correspondence should be addressed. E-mail: msim@eie.gr. ² National Hellenic Research Foundation. ‡ Athens University. (1) Bertrand, J. A.; Cotton, F. A.; Dollase, W. A. J. Am. Chem. Soc. 1963, 85, 1349. (2) Robinson, W. T.; Fergusson, J. E.; Penfold, B. R. Proc. Chem. Soc., London 1963, 116. (3) Bertrand, J. A.; Cotton, F. A.; Dollase, W. A. Inorg. Chem. 1963, 2, 1166. (4) Cotton, F. A.; Haas, T. E. Inorg. Chem. 1964, 3, 10. (5) Mealli, C.; Prosperio, D. M. Comments Inorg. Chem. 1989, 9, 37. (6) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms, 2nd ed.; Oxford University Press: New York, 1993; and references cited therein. (7) Walton, R. A. J. Cluster Sci. 2004, 15, 559. (8) Trogler, W. C.; Ellis, D. E.; Berkowitz, J. J. Am. Chem. Soc. 1979, 101, 5896. Bursten, B. E.; Cotton, F. A.; Green, J. C.; Seddon, E. A.; Stanley, G. G. J. Am. Chem. Soc. 1980, 102, 955. (9) Psaroudakis, N.; Mertis, K.; Liakos, D. G.; Simandiras, E. D. Chem. Phys. Lett. 2003, 369, 490. (10) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms, 2nd ed.; Oxford University Press: New York, 1993; pp 536-548 and references cited therein. Figure 1. Schematic drawing of the structure of 1. Cl4-6 are bridging, Cl7-9 are equatorial, and Cl10-15 are axial. Inorg. Chem. 2007, 46, 2167-2172 10.1021/ic061862p CCC: $37.00 © 2007 American Chemical Society Inorganic Chemistry, Vol. 46, No. 6, 2007 2167 Published on Web 02/10/2007