Structural/bonding insights from new geometrical varieties of two Pt-Au carbonyl/phosphine clusters, [Pt3(AuPPh3)5(μ2-CO)2L3]+ (L3 = (CO)2PPh3) and [(μ6-Au){Pt3(μ2-CO)3L4}2]+ (L = PMe3)

Structural/bonding considerations of two new Pt-Au clusters, [Pt-3(AuPPh3)(5)(mu(2)-CO)(2)(CO)(2)PPh3](+) (1) and [(mu(6)-Au){Pt-3(mu(2)-CO)(3)(PMe3)(4)}(2)](+) (2) isolated (as chloride salts), revealed: (i) that the heretofore unknown 20-electron Pt-centered Pt2Au5 icosahedral cage fragment (five missing vertices) of 1 is best viewed as a 44-electron triangular Pt-3 adduct of a nearly planar 39-electron [Pt-3(mu(2)-CO)L-2(3)](+) (L-3 = (CO)(2)PPh3) and five one-electron donating AuPPh3 ligands; and (ii) that the geometrically distorted trimethylphosphine "full" Pt3AuPt3 sandwich of 2 is the first example of two nucleophilic 44-electron triangular Pt-3(mu(2)-CO)(3)L-4 (3 : 3 : 4) units (L = PMe3) which asymmetrically encapsulate a central electrophilic Au(I).