[(CO)AuCl] reacts with equimolar amounts of PhzPCH,P(Se)Ph2 (dpniSe) to afford CIAuPhzPCHzP(Se)Phz, in which dpmSe is bound to gold in a monodentate fashion by phosphorus. Subsequent reaction of this 1: 1 complex with AgC104 results in the formation of the 10-membered ring complex 4 which crystallizes in the monoclinic space group E1/n with approximately centrosymmetric dicationic units, in which two gold(1) atoms are doubly bridged by two dpmSe ligands coordinated by phosphorus and selenium. The coordination at the gold atoms deviates from linearity and implies an Au-.Au interaction with the gold(1) atoms separated by a distance of 3.020(1) A.As evidenced by the number of review articles and monographs published in recent years 1-6), inorganic and organometallic chemistry of gold is an ever expanding area of research. For the purpose of promoting metal nucleation, which is important, for example, in the controlled deposition of gold in micro-electronics and electron microscopy, extensive studies habe been undertaken on dinuclear gold@) complexes. Initial studies focused on 1,3-difunctional ligands, and several compounds with the 8-membered ring structure 1 have been synthesized. Short transannular Au-.Au contacts are observed in all of these complexes. Weak bonding appears to be operative perpendicular to the linear X-Au-X' axes and can be described as a 5d1"-5d" interaction based on a mixing with the 6s orbitals19), whose energy is lowered by relativistic effects", 'l). Many authors, however, have suggested that there are no significant bonding interactions involved as short Au-Au distances are perhaps not surprising for gold atoms constrained by ring geometry and the small bite of the 1,3-difunctional ligands. The frequency of occurrence of short Au -Au distances in various other types of complexes, however, is not consistent with this view.Clearly, the fixation of metal atoms in close geometrical proximity becomes less favourable as the number of atoms separating the ligand donor atoms increases. A recent report2') has provided evidence for the existence of an attractive interaction between gold(1) centres based on changes in the conformation of the butadiene skeleton. The s-trans ground state geometry of 2,3-bis(diphenylphosphino)-1,3-butadiene is abandoned upon double complexation with AuCl, and the two gold atoms are brought into contact at a distance of 3.023(1) A. If it is assumed that the s-trans to s-cis reorientation is caused by Au...Au attraction, the bond energy is estimated to be in the order of 7 kcal/mol. This result is in good agreement with that arrived at for the analogous system with the 1,4-difunctional ligand 1,l'-bis(dipheny1phosphino)bicyclopropyIz3). In the 10-membered ring complex [ A U~( S C H~C H~P E~~)~] the S-Au-P angle of 173.5" is also adduced as evidence for a Au...Au interaction") since the deviation from linearity is such as to bring the metal atoms closer together.In an effort to further investigate the influence of the weak attractive force between closed-shell (d"-d") centr...
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