The melting behaviour and transport properties of straight chain alkanes mono- and difunctionalized with phosphonic acid groups have been investigated as a function of their length. The increase of melting temperature and decrease of proton conductivity with increasing chain length is suggested to be the consequence of an increasing ordering of the alkane segments which constrains the free aggregation of the phosphonic acid groups. However, the proton mobility is reduced to a greater extent than the proton diffusion coefficient indicating an increasing cooperativity of proton transport with increasing length of the alkane segment. The results clearly indicate that the "spacer concept", which had been proven successful in the optimization of the proton conductivity of heterocycle based systems, fails in the case of phosphonic acid functionalized polymers. Instead, a very high concentration of phosphonic acid functional groups forming "bulky" hydrogen bonded aggregates is suggested to be essential for obtaining very high proton conductivity. Aggregation is also suggested to reduce condensation reactions generally observed in phosphonic acid containing systems. On the basis of this understanding, the proton conductivities of poly(vinyl phosphonic acid) and poly(meta-phenylene phosphonic acid) are discussed. Though both polymers exhibit a substantial concentration of phosphonic acid groups, aggregation seems to be constrained to such an extent that intrinsic proton conductivity is limited to values below sigma = 10(-3) S cm(-1) at T = 150 degrees C. The results suggest that different immobilization concepts have to be developed in order to minimize the conductivity reduction compared to the very high intrinsic proton conductivity of neat phosphonic acid under quasi dry conditions. In the presence of high water activities, however, (as usually present in PEM fuel cells) the very high ion exchange capacities (IEC) possible for phosphonic acid functionalized ionomers (IEC >10 meq g(-1)) may allow for high proton conductivities in the intermediate temperature range (T approximately 120 -160 degrees C).

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Two novel phosphonic acid-based "dry" proton exchange membrane materials that may allow for fuel cell operation above 100 degrees C have been prepared and characterized via solid-state 1H and 2H MAS NMR spectroscopy. We obtained information on both the nature of hydrogen bonding and local proton mobilities among phosphonic acid moieties. In particular, 2H MAS NMR line shape analysis yielded apparent activation energies of the underlying motional processes. Using this approach, we have investigated both a model compound and a novel PEM system. It was found that the relation of estimated hydrogen-bond strength and local proton mobility accessible by solid-state NMR and bulk proton conductivity is complex. Improvements through admixture of a second component with protogenic groups are suggested.

Solid-state double-resonance and triple-resonance 13C, 11B, and 1H NMR experiments are used to investigate two main group metallocene complexes:  the decamethylcyclopentadienylborinium cation, [Cp*2B]+, and bis(pentamethylcyclopentadienyl)methylborane, Cp*2BMe. The crystal structure for the latter complex is reported herein. A combination of magic-angle-spinning and static 11B{H} NMR experiments are used to measure 11B nuclear quadrupole coupling constants (C Q) and rare instances of anisotropic boron chemical shielding tensors. Boron-11 nuclear quadrupole coupling constants reflect the higher spherical symmetry of [Cp*2B]+ compared to Cp*2BMe, with C Q(11B) = 1.14 MHz in the former and C Q(11B) = 4.52 MHz in the latter. Chemical shielding tensor spans are measured for [Cp*2B]+ and Cp*2BMe as Ω = 73.0 and 146.0 ppm, respectively. Hartree−Fock and hybrid density functional theory (B3LYP) calculations of electric field gradient and chemical shielding tensors are in quantitative agreement with experiment, and are applied to examine the relationships between the anisotropic NMR interaction tensors and the structure and symmetry of these chemically analogous but structurally dissimilar boron complexes. Variable-temperature 11B MAS NMR, 13C CPMAS NMR, and 13C/11B/1H CP TRAPDOR NMR experiments are applied to make a preliminary investigation of motion of the Cp* rings of [Cp*2B]+.

The effect of a layer of electrochemically grafted 4-diazo-N,N-diethylaniline (DEA) groups on the electron transfer kinetics of redox systems, displaying fast and slow heterogeneous electron transfer rate constants at edge and basal planes of carbon, was investigated. The properties of the modified electrode were characterized by cyclic voltammetry using four different inorganic redox systems (Fe(CN) 3À=4À 6 , Co(phen) , and IrCl 2À=3À 6 Þ in acidic, neutral, and basic media. Two distinct blocking behaviors and electrostatic effects were observed. More precisely, a strong blocking effect of the grafted layer on Fe(CN) 3À=4À 6 and Co(phen) 2þ=3þ 3 was found, whereas Ru(NH 3 ) 2þ=3þ 6and IrCl 2À=3À 6 showed to be rather unaffected by the presence of the DEA grafted layer.