Folds Bridging

Mixture of on-top (ri ) and two-fold bridge (though the three-fold hollow site is not excluded)... 

On Pt, the mode of isocyanide adsorption depends on the nature of the Pt substrate and perhaps on the nature of the isocyanide. On Pt(lll), CH3NC adsorbs by both T (low coverage) and p,2-T h (high coverage) modes. On Pt nanoparticles, only T adsorption is observed for n-dodecyl isocyanide, but on Pt nanoparticle electrodes evidence suggests that DMPI adsorbs by T (on-top), X2-T t (two-fold bridge) and X2-tl T T (three-fold hollow) modes. 

The firm identification of the alkylidyne group was particularly unexpected. These are almost certainly adsorbed on triangular 3-fold bridging sites on (111)... 

Sequential dosing with 13to and 13co indicate that above 0.5 coverage (c(2x2))CO probably enters vacant linear sites, displacing neighbouring CO molecules into two-fold bridge sites. 

In examples (a) to (c), the locations of the adsorbed atoms differ in that they are (a) end-on, (6) in a two-fold bridging position, and (c) in a three-fold well position in relation to the substrate atoms. However, the outer surface net is the same in each case and, as such, contributes to the same diffraction pattern. In example (d), the alternative unit meshes shown are both correct and both would lead to the same ultimate interpretation, but the C(2 x 2) unit mesh offers the greater convenience. 

Vogtle et al. submitted a mixture of cyclic tetrasulfones 169 and 170 (the sulfide products of the cyclization were not separated but directly oxidized) to a sulfone pyrolysis at 600 °C [61], However, the product was shown not to be the desired four-fold-bridged cyclophane but a doubly clamped 1,2-dihydrocyclobutabenzene. Only an increase of the pyrolysis temperature to 750 °C led to successful formation of the desired [2.2.2.2](l,2,4,5)cyclophane 171 in the mixture of products. Manyfold ort/io-clamped phanes prior to this work were not accessible by sulfone pyrolysis. 

Stractural models of the Pd(l 1 l)-c(2V3x3)-iect-C6H6 adlattice are proposed in Figs. 9(A) and 9(B). In Fig. 9(A), each benzene molecule is spread out over four metal-surface atoms but centered on two-fold bridging sites this helps rationalize the dumb-bell shape of the aromatic molecules. To account for the pseudo-triangular shape of the molecular image, the model in Fig. 9(B) is... 

Figure 9. (A) and (B) Schematic illustrations of two possible real-space structures of the Pd(lll)-c(2V3x3)-rect-C6H6 adlayer. In (A), the benzene molecules occupy two-fold bridge sites in (B), the slightly tilted admolecules occupy three-fold hollow sites. (C) Real-space structural model of the Pd(lll)-( 3x3)-C6H6 adlayer all molecules are situated on three-fold hollow sites.

Two stmctural models for the (3x3)-Q adlattice, each consistent with the present results, are depicted in Fig. 17. In the first, the O atoms occupy atop sites in the second, the O atoms are located at two-fold bridge sites. Unfortunately, the EC-STM images obtained in this study are unable to differentiate between the two possible models. In both stmctnres, the center of the quinonoid ring is located on a two-fold site. 

Focusing our interest towards special sites available for adsorption, W g(Ar) for a nearest-neighbour vector Ar directly yields the fraction of (two-fold) bridge-sites between unlike atoms. Unfortunately, A(Ar) or W gCAr) do not directly yield the number of three-fold or four-fold hollow sites neighbouring, e.g., only atoms of type A. Nevertheless, we will see that the value of also gives an indication whether such sites are more or less common than in a random alloy surface. 

CO adsorbed on a Ru(0001) electrode gave IR bands from linear (1970-2040 cm 1) and three-fold bridging (1770-1820 cm-1) carbonyl systems.127 The IR spectrum of CO adsorbed on a ruthenium-modified Pt(100) surface includes a... 

Figure 8. a) Schematic view of the surface structure of an ideal RuOid 10) singlecrystal, where solid circles represent Ru atoms in the surface plane, open circles O atoms in the surface plane, and dotted open circles O atoms below surface plane b) model of an ideal RuO2(110) single-crystal. Ihe RuO2(110) surface contains two kinds of coordinatively unsaturated (CUS) atoms two-fold bridging O (Obr) and five-fold Ru (Rucus)- The Ojf is the O atoms that lay in the plane in the Ru atoms and posses its bulk-like three-fold coordination. 

The synthesis of 79, 80 and related spiranes has been of interest because of their potential conversion to centrohexacyclic derivatives bearing three additional bridges across the neopentane carbon atoms C-9, C-10 and C-l l,in analogy to some unusual non-benzoannelated analogues such as the Simmons-Paquette molecule [37,81,82]. In fact, triptindanetrione 72 has been used in several cases to construct three additional five-membered rings (Schemes 15 and 56). A surprisingly efficient three-fold bridging with aliphatic diatomic units has been achieved by treatment of 72 with an excess of lithium acetylides. In this way, centrohexacyclic triptindanes 81-83 and related compounds have become accessible, as shown in Scheme 15 [83]. 

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