The preparation, spectroscopic characterization and X-ray structure of thesalt [Pt(eta(1)-C6H9)(Cy2PCH2CH2PCy2)(PPh3)] HCO3 center dot 3H(2)O containing the discrete, uncoordinated, hydrogen-bonded dimeric bicarbonate dianion [(HCO3)(H2O)(3)](2)(2-)

Reaction of the cyclohexyne-platinum(0) complex [Pt(eta(2)-C6H8)(Cy2PCH2CH2 PCy2)]* with water and CO2 in the presence of triphenylphosphine gives the bicarbonate salt of the (eta(1)-cyclohexenyl)platinum(II) cation, [Pt(eta(1 )-C6H9)(Cy2PCH2CH2PCy2)(PPh3)] [HCO3] . 3H(2)O, which has been characterize d by n.m.r. spectroscopy and single-crystal X-ray diffraction at low temper ature. Crystals are triclinic, space group <P(1)over bar> with unit cell di mensions a 20.315(2), b 12.782(1), c 10.694(1) Angstrom, alpha 66.61(1), be ta 104.73(1), gamma 102.11(1)degrees, and Z 2. The structure was refined to a final R value of 0.036 with use of 7553 reflections [I > 3 sigma(I)]. Th e cation has the expected, somewhat distorted planar coordination geometry; the anion consists of discrete, hydrogen-bonded dimers [(HCO3)(H2O)(3)](2) (2-).