The dissolution of PtO2 in concentrated H2SO4 under an atmosphere of CO results in the formation
of hexacarbonyldiplatinum(I), [{Pt(CO)3}2]2+ (1), the first homoleptic, dinuclear, cationic platinum carbonyl
complex, of which a prolonged evacuation leads to reversible disproportionation to give cis-[Pt(CO)2]2+
(solv)
(2) and Pt(0). 1 has been completely characterized by NMR (13C and 195Pt), IR, Raman, and EXAFS
spectroscopy. The structure of 1 is rigid on the NMR time scale at room temperature. NMR: δ(13CA) 166.3,
δ(13CB) 158.7, δ(195Pt) −211.0 ppm; 1
J(Pt−CA) = 1281.5 Hz, 1
J(Pt−CB) = 1595.7 Hz, 1
J(Pt−Pt‘) = 550.9
Hz. The strongly polarized, sharp Raman band at 165 cm-1 (ρ = ca. 0.25) indicates the presence of a direct
Pt−Pt bond. The IR and Raman spectra in the CO stretching region are entirely consistent with the presence
of only terminal CO's on a nonbridged Pt−Pt bond with D
2
d
symmetry. ν(CO)IR: 2174 (E), 2187 (B
2), and
2218 cm-1 (B
2); ν(CO)Raman: 2173 (E), 2194 (B
2), 2219 (B
2), 2209 (A
1) and 2233 cm-1 (A
1). EXAFS
measurements show that the Pt−Pt bond is 2.718 Å and the mean length of the Pt−C bonds is 1.960 Å. The
geometric optimization for 1 by a density functional calculation at the B3LYP level of theory predicts that the
dinuclear cation contains two essentially planar tricarbonyl platinum(I) units that are linked via a Pt−Pt bond
about which they are twisted by exactly 90.0° with respect to each other.