the welghted average of y, and ys (25). Therefore, T h e resulting interfacial energies ysi and yMf and the interfacial energy difference Ay(f) = yblfysi are shown in Fig. 3, A and B. yxlf = ysf at f = 0.57 2 0.05. T h e uncertainty in f results from uncertainties in http://www.sciencemag.org SCIENCE VOL. 275 7 MARCH 1997

Oxo complex [(1,5-COD)4Pt4(mu3-O)2Cl2](BF4)2 (1) reacts readily with ethylene and norbornylene. The ethylene reaction yields acetaldehyde and a 1:1 mixture of (1,5-COD)Pt(Cl)(CH2CH3) (2) and [(1,5-COD)Pt4(eta3-CH2CHCH(CH3))](BF4) (3), while the norbornylene reaction yields a platinaoxetane complex, the first metallaoxetane to be obtained from the reaction of an oxo complex and an alkene.

Three new types of platinum(II) oxo complexes[(1,5-COD)Pt(μ3-O)(AuL)]2(BF4)2 [1, L = PPh3, PPh2Et, PPh2-i-Pr, P(o-tol)3, P(p-tol)3, P(p-MeOC6H4)3, P(p-CF3C6H4)3], [(1,5-COD)Pt{μ3-O(AuL)2}2](BF4)2 (2), and [(1,5-COD)4Pt4(μ3-O)2Cl2]X 2 (3, X = BF4; 3a, X = CF3SO3)are obtained from oxo/chloro exchange reactions between (1,5-COD)PtCl2 and [(LAu)3(μ3-O)]BF4. Crystals of 1 (L = PPh3) from CDCl3 are triclinic, P1̄, with (−100 °C) a = 9.187(4) Å, b = 12.149(3) Å, c = 17.680(6) Å, α = 99.58(2)°, β = 102.86(2)°, γ = 111.63(2)°, V = 1720(1) Å3, and Z = 1. Crystals of 3a from CH2Cl2/toluene are trigonal, P3121, with a = 11.8878(4) Å, c = 29.3193(15) Å, V = 3588.3(3) Å3, and Z = 3. The structure of the cationic portion of 1 shows a planar (COD)Pt(μ-O)2Pt(COD) unit with slightly out-of-plane LAu+ groups linearly coordinated to the oxo ligands. The structure of the cationic portion of 3a is similar and shows a slightly folded (COD)Pt(μ-O)2Pt(COD) unit with out-of-plane [(COD)PtCl]+ groups coordinated to the oxo ligands. Solutions of 3 in untreated CH2Cl2 or CD2Cl2 deposit crystals of [(1,5-COD)4Pt4(μ3-O)2(μ2-OH)](BF4)3 (4) which are monoclinic, P21/n, with a = 18.624(4) Å, b = 14.760(2) Å, c = 15.584(5) Å, β = 95.538(12)°, V = 4264(2) Å3, and Z = 4. The core structure of the cationic portion of 4 shows a tetranuclear platinum cation in which the metal atoms occupy the corners of a distorted tetrahedron and two μ3-oxo ligands and one μ2-hydroxo ligand bridge the four platinum atoms. Reaction of 1 (L = PPh3) with PPh3 gives OPPh3 and [(Ph3P)3PtAuPPh3]BF4 (5) which is also obtained from (Ph3P)4Pt and Ph3PAuBF4. Crystals of 5 from THF are monoclinic, P21/c, with a = 20.426(6) Å, b = 13.4980(11) Å, c = 24.703(9) Å, β = 97.166(15)°, V = 6758(3) Å3, and Z = 4. The structure of 5 consists of an L3Pt−AuL cation where the Au atom is linear 2-coordinate and the Pt atom is distorted square-planar 4-coordinate.

Not only AuAu but also RhAu interactions are responsible for the unusual trigonal‐pyramidal coordination of the oxygen atoms in the complex cation 1. The picture on the right shows the Au4Rh2O2 core of the cluster with norbornadiene (nbd) ligands at the Rh centers; the phosphane ligands have been omitted. The synthesis of this novel heteronuclear cluster is relatively simple. [{(nbd)Rh[μ‐O(AuPPh3)2]}2]2+ 1

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