Electrostatic Structural Enforcement in Low-Dimensional Solids: Synthesis, Structure, and Electronic Properties of Polycationic Ruthenium Complexes with Polycyanoanions

Michael D. Ward, Paul J. Fagan, Joseph C. Calabrese, David C. Johnson

Research output: Contribution to journalArticlepeer-review

Abstract

New low-dimensional solids orenared from nolvcvanoanions and CD*Ru(η-C6Me6)+ (D+: Cp* = C5Me5). (Cp*Ru)266-[22](1,4)cyclophane)2+ (D+-D+), and [Cp*Ru(η-C6H5)]4E4+ ((D+)4E: E = C, Si) demonstrate that the polycations structurally enforce the solid-state structure, with anions adopting stacking motifs that reflect the spatial distribution of charge in the polycations. The mononuclear D+ cation forms dimorphs with TCNQ- (TCNQ = tetracyanoquinodimethane) with the empirical formula [D+] [TCNQ-]. One of these (1) crystallizes with 1-D mixed stacks of cations and TCNQ- anions, whereas the other phase (2) possesses discrete D+A-A~D+ units with a (TCNQ)22- π-dimer situated between two cations. Segregated stacking motifs that are rather common for the TCNQ- anion are not observed. However, structural enforcement provided by the ruthenium centers in the rod-shaped D+-D+ dication affords different structural motifs in [D+-D+] [(TCNQ)x2-] (3, x = 2; 4, x = 4). Nonconducting 3, prepared by electrochemical reduction of TCNQ in the presence of the dication at -0.1 V (vs. Ag/AgCl), possesses mixed stack linear chains with alternating cations and (TCNQ)22- π-dimers, i.e., a…D+-D+A~A-D+-D+A-A-… motif. In contrast, 4 crystallizes as conductive black parallelepipeds by slow electrochemical reduction of TCNQ in the presence of the dication at potentials more positive than E° (tcnq/tcnq-) and possesses two crystallographically unique TCNQ stacks parallel to the long axes of the cations. The distance between cationic Ru sites in D+-D+ accommodates four TCNQ molecules with an overall (2-) charge; the resultant mixed valent ° = 0.5 stacks afford a room temperature conductivity of 0.2 Ω-1 cm-1. The solid-state structures of the nonconducting charge-transfer salts [D+-D+]|C3[C(CN)2]3-)2 (5) and [(D+)4E]{C3[C(CN)2]3-}4.x MeNO 2 (6, E = C, x = 6; 7, E = Si, x = 4) exhibit linear chains of C3[C(CN)2]3- anions. For 5, the anion stacking axis is parallel to the dications, whereas 6 and 7 possess mutually orthogonal anion stacks that are aligned parallel to the orthogonal axes defined by two pairs of cationic centers in the tetracations. Magnetic susceptibility and EPR data for 4 indicate the presence of an energetically accessible triplet state 0.08 eV above the singlet ground state with zero field splitting constants |D↿ = 66 G and |E↿ = 11 G. The EPR spectra of 5–7 also indicate the presence of energetically accessible triplet species. However, magnetic susceptibility measurements indicate strong antiferromagnetic coupling of the anion spins, suggesting that these triplet species are due to impurities or crystalline defects.

Original languageEnglish (US)
Pages (from-to)1719-1732
Number of pages14
JournalJournal of the American Chemical Society
Volume111
Issue number5
DOIs
StatePublished - Mar 1989

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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