S.C. Huckett

New chain materials from binuclear metal complexes

Abstract Reaction of Ru 2 (O 2 CR) 4 (RH, Me, Et, n-Pr, Ph) and bis(2,5-dimethyl-N,N′-dicyanoquinonediimine) (DMDCNQI) produces blue/black to purple materials. On the basis of analytical and spectral data these compounds are formulated as linear chains of Ru 2 5+ metal centers bridged by radical anionic DMDCNQI ligands.

Resonance Raman and far-infrared studies of isotopically disordered and mixed-halide halogen-bridged platinum chain solids

Abstract The MX chain solids [Pt(en) 2 ][Pt(en) 2 X 2 ](ClO 4 ) 4 , (en = C 2 H 8 N 2 and X=Cl, Br), referred to as “PtX”, are used to explore some of the surprising spectral consequences of disorder in 1-D systems, first for pure PtCl, where the disorder arises from randomly distributed Cl isotopes, then for the more drastic case of the mixed-halide materials PtCl 1−x Br x . Lattice dynamics and Peierls-Hubbard modelling are used to analyze the observed spectral behavior. In both cases, the complex structure seen in the Raman and IR spectra is found to arise from strongly localized vibrational modes residing on chain segments, defined by sequences of Cl isotopes for PtCl, and by sequences of Cl and Br for PtCl 1−x Br x .

Far-infrared and resonance raman spectroscopy and isotopic substitution studies of halogen-bridged platinum chain solids

Here we our most recent results on the vibrational spectroscopy of the MX chain solids [Pt(en)[sub 2]][Pt(en)[sub 2]X[sub 2]](ClO[sub 4])[sub 4], (X=Cl, Br or I, and en = C[sub 2]H[sub 8]N[sub 2]), referred to as PtX. Isotopic substitutions are used to clarify the nature of various vibrational modes. For Raman spectroscopy, fundamental phonon frequencies are determined, when possible, by excitation far below the band edge using a Ti:Sapphire laser, thus avoiding defect production, while photo-induced defects are studied specifically after intentional production.

On the origin of the hyperfine structure in the photoinduced EPR spectrum of [Pt(en)2]Pt(en)2Cl2](ClO4)4

Abstract The nitrogen isotope dependence of the EPR spectrum of the photoinduced paramagnetic defects in the halide-bridged platinum linear chain complex [Pt(en) 2 ][Pt(en) 2 Cl 2 ](ClO 4 ) 4 (en = ethylenediamine) has been studied in order to clarify the origin of the 16G hyperfine structure which is superimposed on the 180G hyperfine pattern due to two equivalent Pt nuclei. An earlier study attributed the 16G pattern to the equatorial chelating nitrogens: however, we find that the EPR spectrum obtained for the 15 N-substituted species is identical to that obtained for the normal isotopic species, demonstrating that these off-axis nitrogens are not the origin of this splitting. On the basis of this observation and simulations of the EPR spectrum, we attribute the 16G hyperfine pattern to coupling with three or more chlorine nuclei on the chain axis. The origin of the photoinduced paramagnetic defect in PtCl, whether polaronic or neutral kink soliton, is discussed in view of this new data. These results clearly demonstrate the importance of including halide orbitals in many-body models of the quasi-one-dimensional MX chain solids.

On the origin of the resonance Raman γ1 dispersion and fine structure of PtBr

Abstract The standard preparative route to [Pten2][Pten2Br2](ClO4)4 (PtBr, where en = H2NCH2CH2NH2) results in Cl− impurities in the product. A study of resonance Raman (RR) spectra of PtBr as a function of chloride ion doping illustrates that the 166 cm−1 component of the RR spectrum corresponds to the chain axis ν1 mode. Previously reported ν1 dispersion and fine structure and several other resonance enhanced defect vibrations are shown to result from chloride doping of the PtBr solid.

The effect of chloride doping on the crystal structure of the mixed-valence linear chain [Pten2][Pten2Br2](ClO4)4

Abstract Chloride ion doping of [Pten 2 [Pten 2 Br 2 ](ClO 4 ) 4 (PtBr, where en = H 2 NCH 2 CH 2 NH 2 ) results in crystalline solids with a solid solubility that ranges from pure PtBr to pure PtCl. The previously reported monoclinic and orthorhombic forms of PtBr are shown to arise form differing chloride impurity concentrations and resulting changes in critical temperatures (T c ). Similar structural phase transformations for pure PtBr, PtBr (55% Cl), and PtCl were observed (T c = 28.7, 25.5, 19.8° C , respectively).

Structural phase transition in the quasi-one-dimensional PtCl

Abstract We report on the pulsed neutron powder diffraction study of the high and low temperature phases of [Pt(en)2][Pt(en)2Cl2](CIO4)4 (where en=ethylenediamine), referred to as PtCl, that undergoes a structural phase transition at 19.8°C. It is shown that the high and low temperature phases are orthorhombic and monoclinic, respectively. The transition is associated with a very large shear (3.9°) and the translationai group of the low temperature phase is not a subgroup of the high temperature phase translationai group; this supports the first order character proposed earlier.