Affordable Access

Publisher Website

Syntheses and properties of genuine organic magnetic conductors: (1:1) and (1:2) salts of ethyl-pyridinium-substituted verdazyl radicals with TCNQ

Authors
Journal
Polyhedron
0277-5387
Publisher
Elsevier
Publication Date
Volume
20
Identifiers
DOI: 10.1016/s0277-5387(01)00651-9
Keywords
  • Verdazyl Radical
  • Tetracyanoquinodimethanide
  • Magnetism
  • Conductivity
  • Semiconductor
  • Crystal Structures
Disciplines
  • Physics

Abstract

Abstract Four kinds of (1:1) and (1:2) salts of 3-(4- and 3-ethyl-pyridinium)-1,5-diphenylverdazyl radical cations with tetracyanoquinodimethanide (TCNQ) anion ([ p-EtPyDV] +[TCNQ] − (1), [ m-EtPyDV] +[TCNQ] − (2), [ p-EtPyDV] +[TCNQ] 2 − (3), and [ m-EtPyDV] +[TCNQ] 2 − (4)) have been prepared, and the magnetic susceptibilities ( χ M) measured between 1.8 and 300 K. The values of χ M T at 300 K are 0.437, 0.383, 0.620, and 0.482 K emu mol −1 for the salts (1), (2), (3), and (4), respectively, and decrease by lowering the temperature. The χ M of the salt (2) follows the Curie–Weiss law with a Curie constant of 0.374 K emu mol −1 and a negative Weiss constant of −2.4±0.2 K in the temperature region 1.8–300 K, indicating disappearance of a net magnetic moment due to the formation of strong spin pairs in TCNQ anion molecules. The χ M of the salt (3) shows a broad maximum at T max = 118 ± 2 K and can be well explained by a singlet–triplet equilibrium model with 2 J / k B = - 190 K The χ M of the salt (4) shows a broad maximum at T max = 9.3 ± 0.5 K The χ M can be well reproduced by the sum of the contributions from: (i) a one-dimensional (1D) Heisenberg antiferromagnetic alternating-chain system with 2 J / k B = - 15.2 K (alternation parameter α= J 2/ J 1=0.4); and (ii) the dimer system with 2 J / k B = - 741 K The magnetic property of (4) was discussed based on the results obtained by crystal structure analysis of (4). On the other hand, the susceptibility of the salt (1) showed anomalous magnetic behavior that cannot be explained by a simple model. The (1:1) salts (1) and (2) are insulators. On the other hand, the pressed pellet conductivity ( σ) of the (1:2) salts (3) and (4) at 20°C was σ=6.9×10 −2 and 1.5×10 −3 S cm −1 with activation energy E A=0.072 and 0.25 eV, respectively, showing the property as semiconductor. The two (1:2) salts (3) and (4) are new, genuine organic magnetic semiconductors.

There are no comments yet on this publication. Be the first to share your thoughts.