The structure/property relationship of the following CT salts, [M(R2pipdt)2][M(mnt)2] (where R2pipdt = N,N'-dialkylpiperazine-2,3-dithione; mnt = maleonitrile-2,3-dithiolate), [R = Me, M = Pd (1a) and Pt (2a); R = Et, M = Pt (2b)],which were previously characterised, and [Pt(R2pipdt)2][Pt(dtcr)2] [R = Me, (3a); R = Et, (3b); dtcr = 4,5-disulfanylcyclopent-4-ene-1,2,3-trionate, known as dithiocroconate] are investigated here. These salts show strong near IR CT bands and semiconducting behaviour. The structural features of 3a are similar to those found for 2a: approximately square planar [Pt(Me2-pipdt)2] dications and regular square planar [Pt(dtcr)2] dianions form an infinite anion–cation one-dimensional stack along the c axis with a Pt···Pt c/2 distance of 3.408 (1) Å. In 3a, a net of weak interactions between the N and O atoms of the cation and of the anion contributes to the alignment of 3a in the stack. However, these interactions do not overcome the less favourable redox properties of the components, that is, promoting CT interactions with respect to the corresponding mnt salts. The specific electrical conductivity of pressed powder pellets ranges from 10–11 to 10–5 Ω–1 cm–1 at room temperature, follows the Arrhenius law with activation energies in the range of 0.2–0.6 eV, and is related to the driving force of the electron transfer. Preliminary photoconductivity measurements performed on the two relatively more conducting samples, 2a and 2b, show a gain in current during illumination, similarly to that observed in organic–inorganic photoconductor CT salts C[ML2] (C2+ is 2,2' or 4,4'-bipyridinium or similar derivatives, L2– = dithiolato), which have been extensively investigated by the Kisch group. Crystal data for 3a: triclinic, P; Z = 2; T = 293(2) K; a = 8.683(2) Å, b = 14.009(5) Å, c = 6.815(2) Å; = 100.58(4)°, β = 98.99(3)°, = 100.69(3)°. R indices (all data) R1 = 0.0516, wR2 = 0.1412.
Electro-Conducting Properties of Charge-Transfer Salts based on Cationic and Anionic Platinum Dithiolenes. Crystal Structure of [Pt(Me2pipdt)2][Pt(dtcr)2]
DEPLANO, PAOLA;MERCURI, MARIA LAURA;PILIA, LUCA;SERPE, ANGELA;CONGIU, FRANCESCO;
2005-01-01
Abstract
The structure/property relationship of the following CT salts, [M(R2pipdt)2][M(mnt)2] (where R2pipdt = N,N'-dialkylpiperazine-2,3-dithione; mnt = maleonitrile-2,3-dithiolate), [R = Me, M = Pd (1a) and Pt (2a); R = Et, M = Pt (2b)],which were previously characterised, and [Pt(R2pipdt)2][Pt(dtcr)2] [R = Me, (3a); R = Et, (3b); dtcr = 4,5-disulfanylcyclopent-4-ene-1,2,3-trionate, known as dithiocroconate] are investigated here. These salts show strong near IR CT bands and semiconducting behaviour. The structural features of 3a are similar to those found for 2a: approximately square planar [Pt(Me2-pipdt)2] dications and regular square planar [Pt(dtcr)2] dianions form an infinite anion–cation one-dimensional stack along the c axis with a Pt···Pt c/2 distance of 3.408 (1) Å. In 3a, a net of weak interactions between the N and O atoms of the cation and of the anion contributes to the alignment of 3a in the stack. However, these interactions do not overcome the less favourable redox properties of the components, that is, promoting CT interactions with respect to the corresponding mnt salts. The specific electrical conductivity of pressed powder pellets ranges from 10–11 to 10–5 Ω–1 cm–1 at room temperature, follows the Arrhenius law with activation energies in the range of 0.2–0.6 eV, and is related to the driving force of the electron transfer. Preliminary photoconductivity measurements performed on the two relatively more conducting samples, 2a and 2b, show a gain in current during illumination, similarly to that observed in organic–inorganic photoconductor CT salts C[ML2] (C2+ is 2,2' or 4,4'-bipyridinium or similar derivatives, L2– = dithiolato), which have been extensively investigated by the Kisch group. Crystal data for 3a: triclinic, P; Z = 2; T = 293(2) K; a = 8.683(2) Å, b = 14.009(5) Å, c = 6.815(2) Å; = 100.58(4)°, β = 98.99(3)°, = 100.69(3)°. R indices (all data) R1 = 0.0516, wR2 = 0.1412.
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