The interaction of muoniated cyclohexadienyl radicals with zeolite environments in NaY, HY, and USY has been studied using mainly avoided level crossing muon spin rotation (ALC-mu SR) spectroscopy, which utilizes spin-polarized positive muons as local probes. A strong interaction of C(6)H(6)Mu with sodium cations in NaY is indicated and leads to significant distortion of the C(6)H(6)Mu structure from planarity, accompanied by large shifts in hyperfine coupling constant (hfcc) values compared to those in bulk benzene. Much weaker interactions of this radical with Bronsted acid sites in USY/HY are deduced from the measured muon and proton hfcc values, indicative of a largely planar radical, that, in contrast to those in NaY, also exhibit a strong dependence on benzene loading. The small shifts in hfcc values seen in USY/HY compared to those in the bulk relate to the nature of OH binding sites and possibly also to effects arising from varying local dielectric constants at different benzene packing densities. The muon ALC resonances in these frameworks exhibit a marked increase in widths at temperatures near 300 K and at low benzene loadings, evidence for molecular dynamics, indicating desorption and reorientation of C(6)H(6)Mu, in marked contrast to the nearly static widths seen in NaY up to 470 K

The temperature-dependent variation of local environment and reorientation dynamics of the small amphiphile 2-phenylethanol in lamellar phase dispersions of the dichain cationic surfactants, 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and dioctadecyldimethylammonium chloride (DODMAC), and the nonionic surfactant, tetra(ethylene glycol) n-dodecyl ether (C12E4), have been determined using avoided level crossing muon spin resonance spectroscopy (ALC-muSR). For cosurfactant radicals the hydrophobic or hydrophilic character of the surrounding media can be determined from their magnetic resonance signatures. Comparison of the three different bilayer-forming surfactant systems shows that the ALC-muSR technique is able to distinguish both major and subtle differences in the partitioning of the cosurfactant radicals between the different systems.

Reaction of trans-[a2Pt(Hampy)2]X2 (a = NH3, 2; a = MeNH2, 3; Hampy = 2-aminopyridine; X = NO3 or ClO4) with an excess of [(en)Pd(H2O)2]2+ in aqueous solution leads to two types of condensation products: (i) tetranuclear PtPd3 species, in which the deprotonated “a” ligands (μ-NH2, μ-MeNH) and the deprotonated amino group of the 2-aminopyridine (ampy) ligands are chelated by two (en)PdII entities and in addition a single PdII ion (without en) cross-links the amido functions of ampy in a nearly linear fashion. The four metal ions thus form a diamond arrangement with a short (<2.5 Å) Pt→Pd dative bond. (ii) Hexanuclear Pt2Pd4 species, in which (en)PdII moieties bridge exclusively amido groups of four ampy ligands in such a way that an open rectangular box (or double cone) is formed. This allows two nitrate counter ions to become inserted in the cavity of the +8 charged cation. Thus in both cases the ampy ligand acts as a μ3-ligand, either in an intramolecular or an intermolecular fashion.

Dynamic H-2 NMR spectroscopy employing line shape studies and spin-lattice relaxation experiments is used to investigate the molecular dynamics of the perdeuterated pyridinium cations in pyridinium tetrafluoroborate in the temperature range between 120 and 290 K. Special interest lies in the two solid-solid phase transitions occurring at 204 K and at 238.7 K. The experimental spectra show that the pyridinium cations perform fast rotation around the pseudo C6 axis at high temperatures. Decreasing the temperature leads to successive slowing down of the rotational motion resulting in nearly completely immobile and preferentially oriented pyridinium cations at 120 K. Simulating the spectra with a 3-site or a 6-site jump model shows that both are appropriate to describe the experimental NMR data. The models yield population probabilities which permit the calculation of the orientational contribution to the polarization and the enthalpy change. For both models distinct deviations from the macroscopic properties are found. We therefore suggest that, in addition to the cation orientation, the classical ferroelectric mechanism operates which has a partly compensating effect. A displacement of anion vs cation sublattice by 0.23-0.25 Angstrom is sufficient to account for the missing polarization contribution. Both these ferroelectric mechanisms are potentially continuous in their onset, which is compatible with second-order transitions, but it appears that they may both be borderline cases between second and first order.

Reaction of trans-[a(2)Pt(Hampy)(2)] X-2 (a = NH3, 2; a = MeNH2, 3; Hampy = 2-aminopyridine; X = NO3 or ClO4) with an excess of [(en) Pd(H2O)(2)](2+) in aqueous solution leads to two types of condensation products: (i) tetranuclear PtPd3 species, in which the deprotonated " a" ligands (mu-NH2, mu-MeNH) and the deprotonated amino group of the 2-aminopyridine (ampy) ligands are chelated by two (en) Pd-II entities and in addition a single Pd-II ion (without en) cross-links the amido functions of ampy in a nearly linear fashion. The four metal ions thus form a diamond arrangement with a short (< 2.5 angstrom) Pt-->Pd dative bond. (ii) Hexanuclear Pt2Pd4 species, in which (en) Pd-II moieties bridge exclusively amido groups of four ampy ligands in such a way that an open rectangular box ( or double cone) is formed. This allows two nitrate counter ions to become inserted in the cavity of the +8 charged cation. Thus in both cases the ampy ligand acts as a mu(3)-ligand, either in an intramolecular or an intermolecular fashion.

Avoided level crossing muon spin resonance (ALC-muSR) studies on the muonated cyclohexadienyl radical derived from the amphiphilic cosurfactant 2-phenylethanol have been used to derive cosurfactant partitioning and local environment information when dispersed in a concentrated lamellar phase dispersion. The study of partitioning at the bilayer/water interface at high surfactant concentrations is technically difficult and has consequently received very little attention. Calibration of the working range of fundamental resonance positions facilitates direct determination of cosurfactant partitioning with respect to the oil/ water environment. Additional resonances yield other information about the local environment such as the degree of ordering at bilayer interfaces, thereby presenting a self-consistent picture of the local environment of the tracer molecule.

Pyridinium tetrafluoroborate is a ferroelectric with a paraelectric-ferroelectric phase transition of second order, which is exceptional for multidirectional ferroelectrics, Avoided-level-crossing muon-spin resonance has been used to show that the Mu substituted aza-cyclohexadienyl radical derived from the pyridinium ions undergoes fast uniaxial rotation around the axis perpendicular to the molecular plane, confirming earlier results by Czarnecki et al. The changes in reorientational dynamics between 239 and 244 K also verify the existence of a phase transition in this range, as found by Czarnecki. Furthermore, the results give strong evidence that superimposed on the rotation there is a wobbling motion of the rotational axis which freezes in at the first transition temperature, T-1 = 238.7 K. (C) 2000 Elsevier Science B.V. All rights reserved.

Mixed-metal (Pt-II, Pd-II) mu-NH2-complexes are readily formed upon reaction of trans-[(NH3)(2)PtL2] (L = 2-aminopyridine- N-1 or pyrazolate-N-1; charges omitted) with [enPd( H2O)(2)](2+).