title: Large effect of a small substitution: competition of dehydration with charge retention and coulomb explosion in gaseous [(bipy(R))Au(mu-O)2Au(bipy(R))]2+ dications.
abstract: Dinuclear gold(III) clusters with a rhombic Au(2)O(2) core and 2,2'-bipyridyl ligands substituted in the 6-position (bipy(R)) are examined by tandem mass spectrometry. Electrospray ionization of the hexafluorophosphate salts affords the complexes [(bipy(R))Au(mu-O)(2)Au(bipy(R))](2+) as free dications in the gas phase. The fragmentation behavior of the mass-selected dications is probed by means of collision-induced dissociation experiments which reveal an exceptionally pronounced effect of substitution. Thus, for the parent compound with R = H, i.e., [(bipy)Au(mu-O)(2)Au(bipy)](2+), fragmentation at the dicationic stage prevails to result in a loss of neutral H(2)O concomitant with an assumed rollover cyclometalation of the bipyridine ligands. In marked contrast, all complexes with alkyl substituents in the 6-position of the ligands (bipy(R) with R = CH(3), CH(CH(3))(2), CH(2)C(CH(3))(3), and 2,6-C(6)H(3)(CH(3))(2)) as well as the corresponding complex with 6,6'-dimethyl-2,2'-dipyridyl as a ligand exclusively undergo Coulomb explosion to produce two monocationic fragments. It is proposed that the additional steric strain introduced to the central Au(2)O(2) core by the substituents on the bipyridine ligand, in conjunction with the presence of oxidizable C-H bonds in the substituents, crucially affects the subtle balance between dication dissociation under maintenance of the 2-fold charge and Coulomb explosion into two singly charged fragments.
authors.affiliation: Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Tyo
authors.forename: A W
authors.initials: AW
authors.lastname: Castleman
authors.forename: Detlef
authors.initials: D
authors.lastname: Schröder
authors.forename: Petr
authors.initials: P
authors.lastname: Milko
authors.forename: Jana
authors.initials: J
authors.lastname: Roithova
authors.forename: Jean Michel
authors.initials: JM
authors.lastname: Ortega
authors.forename: Maria Agostina
authors.initials: MA
authors.lastname: Cinellu
authors.forename: Fabio
authors.initials: F
authors.lastname: Cocco
authors.forename: Giovanni
authors.initials: G
authors.lastname: Minghetti
mesh_terms: D015082:2,2'-Dipyridyl / Q000032:analysis* / Q000737:chemistry; D008024:Ligands; D015394:Molecular Structure; D050607:Organogold Compounds / Q000032:analysis* / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D008024:Ligands; D050607:Organogold Compounds; D015082:2,2'-Dipyridyl