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Structure and Properties of Some New Dihydropyrazine-–Tetracyanoquinodimethane Charge Transfer Salts
Journal of Materials Chemistry (1997)
  • David J R Brook, San Jose State University
  • Tad H Koch, University of Colorado at Boulder
Abstract
Rapid crystallization of acetonitrile solutions containing 4a,8a-diaza-2,6-dioxa-3,4,7,8-tetrahydro-4,4,8,8-tetramethylanthracene-1,++5-dione (DDTTA) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) results in two new polymorphs of the previously reported charge transfer salt DDTTA(TCNQ)2.The first of these {β-[DDTTA(TCNQ)2 ]} crystallizes in the space group P21 /c with cell dimensions a=15.04(2), b=6.953(7), c=16.22(2) Å, beta;=99.4(1)°. The structure of the second polymorph {γ-[DDTTA(TCNQ)2 ]} could not be determined as a result of small crystal size. The new donor, 2,4,4,6,8,8-hexamethyl-2,4a,6,8a-tetraaza-3,4,7,8-tetrahydroanthracene-1,++5-dione (HTTA) also forms a charge transfer salt with TCNQ of composition HTTA·TCNQ·CH3CN. This salt crystallizes in the space group P21 /c with a=8.973(1), b=22.907(4), c=14.048(2) Å, β=96.69(1)°. The magnetic susceptibility of the three new materials and the originally reported structure {α-[DDTTA(TCNQ)2 ]} was recorded as a function of temperature. Ferromagnetic exchange is observed between DDTTA cations in α-[DDTTA(TCNQ)2 ] as a result of the molecular alignment brought about by hydrogen bonding. Hydrogen bonding between cations is also observed in HTTA·TCNQ·CH3CN; however, a slightly different orientation results in weak antiferromagnetic exchange between cations. β-[DDTTA(TCNQ)2 ] and γ-[DDTTA(TCNQ)2 ] also show overall antiferromagnetic exchange. In the DDTTA salts, the TCNQ anions are arranged in stacks resulting in semiconducting behavior. In the α and β phases these stacks are dimerized whereas the magnetic susceptibility of the γ phase suggests the stack is tetramerized. In HTTA·TCNQ·CH3CN the TCNQ anions are arranged in discrete dimers.
Disciplines
Publication Date
1997
Publisher Statement
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Citation Information
David J R Brook and Tad H Koch. "Structure and Properties of Some New Dihydropyrazine-–Tetracyanoquinodimethane Charge Transfer Salts" Journal of Materials Chemistry Vol. 7 (1997)
Available at: http://works.bepress.com/david_brook/19/