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Pt, 1; Pd, 2) and [(Hg)2Au(AuPPh3)8]3+ (3). In contrast, reaction of the 16-electron clusters with Hg22+ salts gave the 18-electron clusters [(HgN03)2M(AuPPh3)8]2+ (M = Pt, 6; Pd, 7). The 18-electron, monomercury clusters [(Hg)M(AuPPh3)g]2+ (M = Pt, 4; Pd, 5) were isolated as intermediates in the formation of clusters 1 and 2 and were also prepared by reaction of clusters 1 or 2 with 1 equiv of [M(AuPPh3)g]2+ (M = Pt, Pd). Clusters 1-7 have been characterized by spectroscopic and analytical methods, and the nitrate salts of 2 and 4, by single crystal, X-ray diffraction. The crystal data for these compounds are as follows: for 2(NOa)2, orthorhombic Fddd, a = 34.66(2) Á, b = 42.09(3) Á, c = 39.29(3) Á, V = 57 329 Á3, Z = 16, residuals R = 0.099 and Rw = 0.098 for 1777 observed reflections and 152 variables, Mo Ka radiation; for 4(NOa)2, monoclinic P2¡ln, a = 16.95( 2) k,b = 31.60(3) k,c = 25.69(3) Á, ß = 94.07(7)°, V = 13 725 Á3 56, Z = 4, residuals R = 0.088 and Rw = 0.081for 7504 observed reflections and 441 variables, Mo Ka radiation. The stmcture of the cluster core of 2(NOs)2 is a Pd centered square-antiprism with bare Hg atoms capping the two square faces. A crystal of the Pt analog, 1(NOs)2, was isomorphous and presumably isostructural to 2(NC>3)2. The structure of 4(NOs)2 is similar to that of 2(NOa)2 with one of the capping Hg atoms removed. A crystal of SCNOsb was isomorphous and presumably isostructural to 4(NC>3)2. The reactions of 1-7 with CO, Cl", and redox agents have been examined. Importantly,

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The rotational correlation time for tris(ethylenediamine)cobalt(III) ion in water has been measured by three nuclear magnetic resonance methods. At 25 °C the rotational correlation time is between 30 and 35 psec. From the change in the correlation time on ion pair formation with phosphate ion it is concluded that the partners in the ion pair rotate as a unit in water.

Nuclear magnetic resonance relaxation time measurements are reported which permit evaluation of the electrostatic contribution to field gradients from ions external to the first coordination sphere of the observed nucleus. It is concluded that for the tris(ethylenediamine)cobalt(III) ion the presence of phosphate ion in the second coordination sphere makes little if any contribution to the electric field gradient at the cobalt nucleus.Considerable attention has been focused on the origins of NMR relaxation in aqueous electrolyte solutions.2 For many nuclei the nuclear electric quadrupole interaction dominates; but definitive evidence that any of the theoretical approaches to this problem is correct is lacking. A theory developed by Hertz focuses on electrostatic contributions to the electric field gradient at the observed nucleus and is able to obtain approximate agreement with experimental observations.3,4 In spite of this result some discussions of NMR data for quadrupole relaxed nuclei have ignored electrostatic contributions to relaxation originating external to the first sphere of interaction and focused only on that part which results from molecules or ions in the first coordination sphere of the observed ion. The present experiment is directed at assessing the validity of this approach.