Choice of Coordination Number in d 10 Complexes of Group 11 Metals M. Angels Carvajal, † Juan J. Novoa, †,‡ and Santiago Alvarez* ,†,§ Contribution from the Centre Especial de Recerca en Quı ´mica Teo ` rica, Parc Cientı ´fic de Barcelona, AV. Baldiri Reixach 10-12, 08028 Barcelona, Spain; Departament de Quı ´mica Fı ´sica, UniVersitat de Barcelona, Martı ´ i Franque ´ s 1-11, 08028 Barcelona, Spain; and Departament de Quı ´mica Inorga ` nica, UniVersitat de Barcelona, Martı ´ i Franque ` s 1-11, 08028 Barcelona, Spain Received September 9, 2003; E-mail: santiago.alvarez@qi.ub.es Abstract: The distribution of di-, tri-, and tetracoordination among the d 10 ions of the group 11 metals is theoretically analyzed by means of density functional calculations on more than 150 model complexes of general formula [MX mL n] (1-m) (where M ) Cu, Ag, or Au; L ) NH3 or PH3;X ) Cl, Br, or I; m + n ) 2-4). The energy of a ligand association reaction has been found to be practically determined by two contributions: the interaction energy and the energy of deformation of the metal coordination sphere. The larger deformation energy of gold complexes compared to copper and silver ones explains the predominance of dicoordination among Au I complexes, in comparison with Cu I and Ag I , for which dicoordination is far less common than tri- and tetracoordination. Other experimental trends can be explained by looking at the fine details of these two energetic components. Introduction The d 10 ions of the group 11 transition metals present variable coordination numbers, offering one of the most challenging cases for the a priori prediction of the structure expected for a given combination of metal ion and ligands. Hence, one can find many dicoordinate linear molecules but also trigonal planar or tetrahedral complexes. In addition, the distribution of these coordination numbers is clearly different for Au than for the lighter elements of the group, as illustrated in Figure 1. Thus, while Cu I and Ag I are most commonly found as tetracoordinate species, Au I appears essentially in linearly dicoordinate com- plexes, even if the existence of tri- and tetracoordinate species is nonnegligible. 1 Although in the gas phase only structures of mono- and dicoordinate complexes have been reported, 2 recent FT ion cyclotron resonance spectrometry showed that Cu I reacts with PH 3 forming the di-, tri-, and tetracoordinate cations, whereas Ag I and Au I only form dicoordinate complexes. 3 Also recent computational studies 4 have found that bonding of additional phosphine ligands to [Au(PH 3 ) 2 ] + and [MCl(PH 3 )] is little favored. A further complication results from the fact that the assign- ment of a coordination number in a particular crystal structure is not always straightforward, and some ambiguity exists in a number of cases (see Supporting Information for more details, Table S1). As an example, in Ag I complexes described as dicoordinate, the L-Ag-L bond angles show a continuous distribution (Supporting Information, Figure S1) between the maximum at 180° and 110°. Deviation from linearity makes us suspect that the smallest bond angles correspond to tricoordinate complexes, as actually found: all molecules with bond angles smaller than 147° are seen to have metal-ligand contacts at less than 2.8 Å, with only one exception. 5 Similarly, many supposedly tricoordinate complexes present either one additional short contact to a donor atom, indicating effective tetracoordi- nation, or one too long “bond distance” that should be considered nonbonding, indicating an effective coordination number of two. Finally, a host of tetracoordinate complexes have either one long metal-ligand bond distance and bond angles consistent with tricoordination or two long bond distances and a nearly linear arrangement of the other two ligands, indicative of effective dicoordination. With all these precedents, three main questions arise: (1) What determines the coordination number for a given choice of d 10 metal ion and ligands? (2) Why Au I has a much greater † Parc Cientı ´fic de Barcelona. ‡ Departament de Quı ´mica Fı ´sica, Universitat de Barcelona. § Departament de Quı ´mica Inorga `nica, Universitat de Barcelona. (1) Gimeno, M. C.; Laguna, A. Chem. ReV. 1997, 97, 511. (2) Vogt, J.; Mez-Starck, B.; Vogt, N.; Hutter, W. J. Mol. Struct. 1999, 485- 486, 249. (3) Harris, H.; Fisher, K.; Dance, I. Inorg. Chem. 2001, 40, 6972. (4) Schwerdtfeger, P.; Hermann, H. L.; Schmidbaur, H. Inorg. Chem. 2003, 42, 1334. (5) Kanatzidis, M. G.; Jun-Hong, C. J. Solid State Chem. 1996, 127, 186. Figure 1. Distribution of the crystal structures of Cu I , Ag I , and Au I compounds according to coordination number of the metal atom as found in the Cambridge Structural Database. Published on Web 01/20/2004 10.1021/ja038416a CCC: $27.50 © 2004 American Chemical Society J. AM. CHEM. SOC. 2004, 126, 1465-1477 9 1465