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Reaction of Na2Mo6Cl8(OMe)6 with CpFeC5H4CO2H produces the new cluster Na2Mo6Cl8(O2CC5H4FeCp)6·HOCH3, which consists of a novel one-dimensional chain from the interactions of the Na+ ions with the carboxylate ligands of adjacent clusters. Coordination of the Na+ cations to the carboxylate ligands is reflected in the vibrational spectroscopy of the sodium salt of [Mo6Cl8(O2CC5H4FeCp)6]2-. Both the [Mo6Cl8]4+ and ferrocenecarboxylate groups are redox active. Voltammetry of the sodium salt of the cluster in DMSO reveals that the ferroceniumcarboxylate ligands dissociate with a rate constant of k = 0.6 s-1. Crystallographic data for Na2Mo6Cl8(O2CC5H4FeCp)6·CH3OH:  monoclinic space group, P21/c (No. 14), a = 13.175(3) Å, b = 25.148(8) Å, c = 11.264(2) Å, β = 92.10(2)°, V = 3729(1) Å3, Z = 2.

Techniques for fabricating nanospaced electrodes suitable for studying electron tunneling through metal-molecule-metal junctions are described. In one approach, top contacts are deposited/placed on a self-assembled monolayer or Langmuir-Blodgett film resting on a conducting substrate, the bottom contact. The molecular component serves as a permanent spacer that controls and limits the electrode separations. The top contact can be a thermally deposited metal film, liquid mercury drop, scanning probe tip, metallic wire or particle. Introduction of the top contact can greatly affect the electrical conductance of the intervening molecular film by chemical reaction, exerting pressure, or simply migrating through the organic layer. Alternatively, vacant nanogaps can be fabricated and the molecular component subsequently inserted. Strategies for constructing vacant nanogaps include mechanical break junction, electromigration, shadow mask lithography, focused ion beam deposition, chemical and electrochemical plating techniques, electron-beam lithography, and molecular and atomic rulers. The size of the nanogaps must be small enough to allow the molecule to connect both leads and large enough to keep the molecules in a relaxed and undistorted state. A significant advantage of using vacant nanogaps in the construction of metal-molecule-metal devices is that the junction can be characterized with and without the molecule in place. Any electrical artifacts introduced by the electrode fabrication process are more easily deconvoluted from the intrinsic properties of the molecule.

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Synthetic routes have been developed that allow attachment of a variety of functional groups to etched, singlecrystal InP surfaces. Benzyl halides, alkyl halides, silyl halides, and esters reacted readily with InP to yield covalently attached overlayers on the semiconductor surface. High-resolution X-ray photoelectron spectroscopy (XPS) revealed that the functionalization chemistry was consistent with the reactivity of surficial hydroxyl groups. Analysis of the XP spectra of the (111)B-oriented (P-rich) face in ultrahigh vacuum revealed signals ascribable to a monolayer of oxidized P atoms on the etched (111)B InP surface. The lack of reactivity of the (111)A-oriented (In-rich) face with these same functionalization reagents is therefore attributed to the difference in the nucleophilicity and acidity of the In and P oxides that are present on the (111)A and (111)B faces, respectively. The coverage of benzylic groups obtained through functionalization of (111)B-oriented InP with benzyl halides was estimated to be 4 × 10 14 cm 2 . This coverage implies that the functionalization can only proceed at alternate surface P atom sites in this system, which is expected from molecular packing considerations of these particular functional groups. Photoluminescence decay measurements were performed to investigate the electrical properties of the etched and modified InP surfaces, and these data indicated that the surface recombination velocity of the functionalized InP surface was ≈10 2 cm s -1 . This low surface recombination velocity implies that <1 electrically active defect is present for every 10 5 atoms on the modified InP surface, indicating that high electrical quality can be maintained while introducing a variety of chemical functionalities onto the (111)B surface of InP.