UV photoelectron spectra of group IV alkyl hydrides

We have had occasion to measure the photoelectron spectra of some heavy group IV alkyls and alkyl hydrides. Although the ionization potentials serve primarily as a body of information which is useful in investigating trends in reactivity for processes involving electron transfer [1], they also provide a pleasing example of the simplicity with which the language of molecular orbital theory can be used to explain trends in the energies and nature of the radical cation states of a series of chemically related molecules [2].     

Dependence of field switched ordered arrays of dinuclear mixed-valence complexes on the distance between the redox centers and the size of the counterions

trans-[(H(2)NCH(2)CH(2)C triple bond N)(dppe)(2)Ru(C triple bond C)(6)Ru(dppe)(2)(N triple bond CCH(2)CH(2)NH(2))][PF(6)](2), 2[PF(6)](2), a derivative of trans-[Cl(dppe)(2)Ru(C triple bond C)(6)Ru(dppe)(2)Cl] functionalized for binding to a silicon substrate, has been prepared and characterized spectroscopically, electrochemically, and with a solid state, single-crystal structure determination. Covalent binding via reaction of one amine group to a boron-doped, smooth Si-Cl substrate is verified by XPS measurements and surface electrochemistry. Vertical orientation is demonstrated by film thickness measurements. Synthesis of the 2[PF(6)](3) mixed-valence complex on the surface is established by electrochemical techniques. Measurement of the ac capacitance of the film at 1 MHz as a function of voltage across the film with a pulse-counter pulse technique demonstrates controlled electric field generation of the two stable mixed-valence forms differing in the spatial location of one electron, that is, switching. As compared to [trans-Ru(dppm)(2)(C triple bond CFc)(NCCH(2)CH(2)NH(2))][PF(6)][Cl], 1[PF(6)][Cl], the magnitude of the capacitance signal per complex observed on switching is shown to increase with increasing distance between the metal centers. Additional experiments on 1[X][Cl] show that the potential for switching 1[X][Cl] increases in the order [X](-) = [SO(3)CF(3)](-) < [PF(6)](-) < [Cl](-). A simple electrostatic model suggests that the smaller is the counterion, the greater is the perturbation of the metal sites and the larger is the barrier for switching.     

Protonation of cluster molecules: Bridging hydrogen sites in tetrahedral,octahedral and capped square pyramidal clusters: Be4H8, Be4H8

Main group structural models for tetrahedral and octahedral transition metal clusters containing bridging hydrogens are developed using the MNDO quantu     

On the validity of the isolobal principle: Pentaborane(9) and its ferraborane derivatives

We have completed Fenske-Hall LCAO-MO-SCF calculations on B₅H₉, 1-Fe(CO)₃B₄H₈, 2-Fe(CO)₃B₄H₈, and 1,2-[Fe(CO)₃]₂B₃H₇. Comparison of orbital contour diagrams of the a₁ and e cluster MO's for B₅H₉ and 1-Fe(CO)₃B₄H₈ demonstrates the validity of the isolobal principle. In addition it is found that the apical and basal BH units of B₅H₉ have practically identical Mulliken overlap populations for framework cluster-type interactions. Further, in all the ferraboranes the 1-Fe(CO)₃ (apical) units have a larger cluster-type Mulliken overlap population than do the 2-Fe(CO)₃ (basal) units. The Fe(CO)₃ units have less electronic charge than do the BH units. The cluster-type Mulliken overlap population for an Fe(CO)₃ group is much less than that of the isolobal BH unit, but this may result from an artifact of the Mulliken overlap population analysis.     

Molecular QCA cells. 1. Structure and functionalization of an unsymmetrical dinuclear mixed-valence complex for surface binding

Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation and functionalization of an unsymmetrical heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The solid state structures of trans-RuCl(dppm)(2)(C[triple bond]CFc) (1) (dppm = methylbis(diphenylphosphane), Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) and mixed-valence [trans-RuCl(dppm)(2)(C[triple bond]CFc)][BF(4)] (1a) as well as XPS and spectroscopic data suggest class II behavior suitable for the intended application. Utilization of the trans-Cl position of 1 permits functionalization for surface binding. Two "tailed" complexes of 1, trans-Ru(dppm)(2)(C[triple bond]CFc)(C[triple bond]CPhOCH(3)) (2) and trans-[Ru(dppm)(2)(C[triple bond]CFc)(N[triple bond]CCH(2)CH(2)NH(2))][PF(6)] (3), have been prepared and characterized. The solid state structure of 3 and multinuclear NMR experiments define the structures. In addition, the spectroscopic properties of all complexes and their mixed-valence species are used to define the effect of the substituent "tail" on mixed-valence properties. Further, the electrochemistry of these compounds permits assessment of the extent of perturbation of the substituents on the comproportionation constants and overall electrochemical stability. The complexes possess properties necessary for candidate QCA molecules.