TY - JOUR
T1 - The Organic Metal (Me2-DCNQI)2Cu
T2 - Dramatic Changes in Solid-State Properties and Crystal Structure Due to Secondary Deuterium Effects
AU - Sinzger, Klaus
AU - Hünig, Siegfried
AU - Jopp, Martina
AU - Bauer, Dagmar
AU - Bietsch, Werner
AU - von Schütz, Jost Ulrich
AU - Wolf, Hans Christoph
AU - Kremer, Reinhard Karl
AU - Metzenthin, Tobias
AU - Bau, Robert
AU - Khan, Saeed I.
AU - Lindbaum, Andreas
AU - Lengauer, Christian L.
AU - Tillmanns, Ekkehart
PY - 1993/8/1
Y1 - 1993/8/1
N2 - Although (R1,R3-DCNQI)2Cu salts (1) are isomorphic (space group I41/a), they behave differently upon cooling: The group M salts remain metallic down to the lowest temperatures, whereas the group M-I salts show phase transitions to semiconductors at temperatures TM-I = 160–230 K. With regard to the steric requirements of the methyl group, 1a (CH3/CH3/H2) is expected to belong to group M-I, but it remains metallic even at 0.4 K (σ = 500 000 S cm−1)- Deuterated 1a, however, namely 1c (CH3/CD3/H2), 1d (CD3/CD3/H2), and 1e (CD3/CD3/D2), undergo sharp phase transitions at 58, 73, and 82 K, respectively, the lowest phase-transition temperatures observed so far for copper salts 1 at ambient pressure. Thereby, conductivities drop by 6–8 orders of magnitude within a few kelvins, transforming 1c-e from three-dimensional into strictly one-dimensional systems. This unprecedented strong secondary deuterium isotope effect is also reflected in significant changes in ESR signals and magnetic susceptibilities. Structure determinations by X-ray analysis of 1a and 1d at various temperatures (20 K, 156 K, and room temperature) reveal characteristic differences of the crystal structures above and below the phase-transition temperature TM-I for both compounds. The very special structural features of the crystals are related to their 7-fold diamondoid superstructure, which includes infinite superhelices in the stacks of ligands and copper ions. A phase diagram of (R1,R3-DCNQI)2Cu salts (1) is derived from a comparison of temperature-dependent structural and conductivity data, which shows that the conductive properties of the salts depend dramatically on the N-Cu-N angle αco.. A minimal threshold value (αco ≈ 126.4°) is evaluated which determines the phase behavior of 1 upon cooling or applying pressure. In order to understand their unique properties as compared to those of other DCNQI metal salts, a new approach to DCNQI copper salts is presented in terms of a “two conductors in one” concept, which is a unique combination of a common one-dimensional (anisotropic) conduction path along segregated stacks and a three-dimensional (isotropic) conduction path within a Robin-Day class III network of delocalized mixed-valent metal ions bridged by organic spacers allowing electron transfer.
AB - Although (R1,R3-DCNQI)2Cu salts (1) are isomorphic (space group I41/a), they behave differently upon cooling: The group M salts remain metallic down to the lowest temperatures, whereas the group M-I salts show phase transitions to semiconductors at temperatures TM-I = 160–230 K. With regard to the steric requirements of the methyl group, 1a (CH3/CH3/H2) is expected to belong to group M-I, but it remains metallic even at 0.4 K (σ = 500 000 S cm−1)- Deuterated 1a, however, namely 1c (CH3/CD3/H2), 1d (CD3/CD3/H2), and 1e (CD3/CD3/D2), undergo sharp phase transitions at 58, 73, and 82 K, respectively, the lowest phase-transition temperatures observed so far for copper salts 1 at ambient pressure. Thereby, conductivities drop by 6–8 orders of magnitude within a few kelvins, transforming 1c-e from three-dimensional into strictly one-dimensional systems. This unprecedented strong secondary deuterium isotope effect is also reflected in significant changes in ESR signals and magnetic susceptibilities. Structure determinations by X-ray analysis of 1a and 1d at various temperatures (20 K, 156 K, and room temperature) reveal characteristic differences of the crystal structures above and below the phase-transition temperature TM-I for both compounds. The very special structural features of the crystals are related to their 7-fold diamondoid superstructure, which includes infinite superhelices in the stacks of ligands and copper ions. A phase diagram of (R1,R3-DCNQI)2Cu salts (1) is derived from a comparison of temperature-dependent structural and conductivity data, which shows that the conductive properties of the salts depend dramatically on the N-Cu-N angle αco.. A minimal threshold value (αco ≈ 126.4°) is evaluated which determines the phase behavior of 1 upon cooling or applying pressure. In order to understand their unique properties as compared to those of other DCNQI metal salts, a new approach to DCNQI copper salts is presented in terms of a “two conductors in one” concept, which is a unique combination of a common one-dimensional (anisotropic) conduction path along segregated stacks and a three-dimensional (isotropic) conduction path within a Robin-Day class III network of delocalized mixed-valent metal ions bridged by organic spacers allowing electron transfer.
UR - http://www.scopus.com/inward/record.url?scp=12044259311&partnerID=8YFLogxK
U2 - 10.1021/ja00070a013
DO - 10.1021/ja00070a013
M3 - Article
AN - SCOPUS:12044259311
SN - 0002-7863
VL - 115
SP - 7696
EP - 7705
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 17
ER -