Susan Jansen

Synthetic, Structural, and Electrical Aspects of Molecular and Polymeric Selenium and Tellurium Materials

Abstract The physical and structural concepts concerning organochalcogen-based anisotropic organic metals are summarized, and the rationales which motivate synthetic activity in new selenium and tellurium materials are presented. An overview of our approach to new aromatic molecular and polymeric materials involving direct thermal reaction of new alkali chalcogenide reagents with unactivated aromatic halides is given, and recent applications to the synthesis of tetraselenonaphth-alene (TSeN) and new transition metal diselenolenes based on o-benzenediselenolate (bds) are noted. The crystal and molecular structures of TSeN and (nC4Hg)4N+ Ni(bds)2′ have been determined, as well as their electronic absorption and electron spin resonance spectra and cyclic voltammetric behavior. The reaction of cis-dichloroethylene and sodium diselenide leads to a polymer to which the repeat sequence ←Se-CH=CH-CH-CR-Se→ is assigned, based on elemental analysis and infrared spectrum.

Comparative Esr Studies of Solid Polycrystalline Alkali Metal Salts of Tcnq and Tcnqf4

Abstract The results of comparative ESR studies of the polycrystalline salts of alkali metal TCNQ and TCNQF4 are presented. The temperature dependence of the relative magnetic susceptibility as determined by ESR techniques is presented. All the TCNQ salts studied show a thermally activated paramagnetism, whereas, at least, one of the TCNQF4 salts follows Curie Law. The principal components of the g-tensors have been measured as a function of temperature. There is considerably more variation in both sets of measurements from alkali metal to alkali metal for the salts prepared from TCNQF4 than there is for those prepared from TCNQ.

ESR and Theoretical Studies of Bis-Benzene-1, 2-Diselenolate Nickel and Related Complexes

Abstract ESR and theoretical studies of the transition metal complexes of [Co and Ni (Se2C6H4)2]− (n-C4H9)4N+ are reported and compared with closely related systems. Room temperature single crystal X-ray studies reveal the Nickel complex is orthorhombic. ESR studies of the polycrystalline powders of the Ni complex as a function of temperature from 108 K to room temperature show a series of spectral envelopes which can arise only from a paramagnetic site which possesses axial symmetry. At ca 160 K, there is an abrupt change in the value of the principal components of the anisotropic g-tensor of the Ni complex which is discussed. Low temperature ESR studies of polycrystalline samples of the ground state triplet Cobalt complex which is isomorphous with the Nickel complex reveal an orthorhombic g-tensor. From the field position of the half-field resonance, it is possible to calculate a mean separation, of the two electrons which make up the triplet state, of 4.3 (±0.5) A.

Magnetic Studies of New Linear Chain Transition Metal Diselenolenes

Abstract The o-benzenediselenolate dianion(bds) reacts with transition metal dichlorides(Co, Ni, Cu) to give new transition metal diselenolenes isolated as tetra-n-butylammonium salts. These materials have been characterized by elemental analysis, cyclic voltammetry, electronic spectroscopy, x-ray diffraction, ESR and static magnetic susceptibility. The crystal structure of (n-C4H9)4 N+Ni(bds)2 reveals a mixed chain structure. This report primarily presents the results of studies of the magnetic properties of Co, Ni and Cu diselenolenes as revealed by ESR and static magnetic susceptibility techniques.

ESR studies of polydiacetylene and related materials

Abstract ESR studies of pristine, partially oriented, polycrystalline poly-[1,6-bis(N-carbazolyl)-2,4-hexadiyne]DCH polydicetylene (PDA)), of the reaction of poly-DCH-PDA with bromine, and of poly-DCHBr6 are reported and compared to previously reported ESR studies on similar systems. The ESR studies include measurements of the spectral linewidths, the g-tensors and the relative ESR signal intensity as a function of temperature for poly-DCH and poly-DCHBr6.

Experimental and theoretical studies of transition metal dithiolate and diselenolate

Abstract The results of comparative physical (especially ESR) studies of bis-benzene-1,2-dithiolate(bdt) and bis-benzene-1,2-diselenolate(bds) transition metal complexes are presented and analyzed in terms of the molecular and electronic structures of these transition metal complexes. The results of Extended Huckel molecular orbital calculations are presented and discussed, also, as an aid toward developing a better and more complete understanding of the magnetic studies presented. These calculations provide such information as the order of the electronic energy levels, composition and symmetries of the molecular orbitals, the total charge density distribution within the molecular complexes, and the charge density distribution within the orbital(s) which contain the unpaired electron(s).

ESR Studies of One-Dimensional Conductors Based on Tetracyanoquinodimethan (TCNQ)

Abstract ESR studies on a series of polycrystalline tetracyanoquinodimethan (TCNQ) based one-dimensional conductors are described. The donors, all of which are diamagnetic, include alkali metals, alkyl/arylphosphines and substituted bipyridinium compounds. The ESR studies include the measurement of the magnetic susceptibility and the anisotropic g-tensor as a function of temperature. Of particular interest, is the information which one can obtain from a careful study of changes in the g-tensor with respect to changes in the crystal and electronic structures(e.g., phase transitions).

Comparative ESR studies of the polycrystalline alkali metal tetrafluorotetracyanoquinodimethan(TCNQF4) charge transfer salts

Abstract The entire series of alkali metal charge transfer salts of tetrafluorotetracyanoquinodimethan(TCNQF 4 ) have been synthesized and studied by electron spin resonance(ESR) techniques. The temperature dependence of the g-tensor, the temperature dependence of the relative magnetic susceptibility and the temperature dependence of the spectral envelope of each salt is discussed. The spectral properties of these salts are discussed in terms of the relationship between the size, electropositivity, and other physical properties of the alkali metal ion as one moves through the alkali metal series. The lithium salt exhibits a temperature independent g-tensor and the magnetic susceptibility follows Curie Law from 77 to 300 K. The ESR envelope of the sodium salt consists of two overlapping spectra. The magnetic susceptibility of both species is thermally activated. The spectral envelopes of the potassium and rubidium salts are similar in shape and behavior. Both are strongly dependent upon temperature. Their magnetic susceptibilities are thermally activated. The potassium salt has been studied from ca 4 to 300 K. An abrupt change in the spectral lineshapes of the potassium and rubidium salts is observed at ca 150 K. Finally, the spectral envelope of the cesium salt displays a unique monotonic decrease in linewidth with temperature.