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Synthesis, structure and properties of [M(diod)2]x− complexes
ELSEVIER
Synthetic
Synthesis,
Structure
Metals
and Properties
A E Underhill, University
71 (1995) 1955-1956
N Robertson
of [M(diod),]“‘ Complexes and D L Parkin
of Wales, Bangor, Gwynedd, LL57 2UW, UK
Abstract Complexes structurally
of the type [TBA][M(diod)J (M = Ni, Cu. Au; diod = 1,4dithia-6-oxa-2.3dithiolate) have been prepared and character&d and spectroscopically. The potential applications of these complexes to the synthesis of highly conducting materials is
discussed. Introduction Metal bis 1.2~dithiolate complexes have been widely studied due to their potential applications in the development of new electrical conductors and superconductors’. The potential to develop materials with improved properties compared with metal dmit complexes has encouraged the preparation of structurally related compounds. Results
and Discussion
We have prepared the complexes [TBA][M(diod)J [M = Ni(l), Cu(2), AU(~)] by the method outlined in scheme 1. The structure of these complexes is analogous to the previously reported organic donor OTT (BOBMT-TTF)*.
chloride gave an immediate precipitate of the product as a brown powder, soluble in polar solvents. The gold complex proved difficult to recrystallise due to the extremely fine nature of the precipitate and was therefore more readily isolated as the tetraphenylphosphonium (TPP) salt. A by-product of the reaction was the insoluble netural complex [M(diod)J. These could also be prepared from the anionic complexes by oxidation with I, in acetone. The complex salts however are of greater importance as precursors for synthetic metals because of their superior solubility and the possibility of converting them to a partially oxidised conducting salt. The crystal structure of l3 shows the structure around the NiS,C,S, core typical for this class of compounds’. Bond lengths lie between values for single and double bonds indicating the delocalised nature of the bonding. The anions adopt a chair conformation with respect to the -CH,-0-CH,-endgroups and form stacks with an intermolecular distance of 8.5A. The large intermolecular separation precludes any intermolecular interaction and this is reflected in the magnetic properties of the complex. Over the temperature range S-290K 1 obeys the CurieWeiss law with 8 approximately equal to zero and with one unpaired electron per molecular unit. Thus the complex exhibited paramagnetic behaviour with no indication of interaction between adjacent spins.
Scheme 1
The thione, obtained in 60% yield from [TEAJ,[Zn(dmit)J. was treated with NaOEt to afford the b&odium salt of the ligand 1.4dithia-6-Ooxa-2,3dithiolat (diod). Addition of the counterion [TBA]’ followed by slow addition of the appropriate metal
0379-6779/95/$09.50 0 1995 Elsevier SSDI 0379-6779(94)03124-O
Science
S.A. All rights
reserved
Complex 1 displays an intense absorption at 940 nm corresponding to the 2b,, to 34 transition observed in monoanion dithiolate?. This band remains unchanged in the solid state reflectance spectrum again indicating no interaction between molecules in the solid state. The presence of this band and a corresponding band at 905 nm for the neutral complex Ni(diod), suggests that these may have applications as a resonance The copper and gold enhanced non-linear optical material. monoanion complexes, with complete occupation of the HOMO and different orbital energies do not display a m-responding transition.
1956
A.E.
Underhill et al. I Synthetic Metals 71 (1995) 1955-1956
Structure
of lTBAI[Ni(diod)J
Complexes 2 and 3 show ‘H nmr signals for the ligand protons at 5.02 and 4.95 ppm respectively. The observation of these signals is in keeping with the expected diamagnetic nature of these complexes. Cyclic voltammetry studies have been carried out in CH,CN against SCE. Complex 1 shows two reversible waves at -0.65V and +0.28V assigned to 2-/l- and l-/O couples respectively. A further irreversible oxidation at +l.l6V was observed which could correspond to the formation of a cationic species. The copper complex 2 shows an irreversible oxidation at +0.56V, assigned as 1- to neunal, and a reduction at -1.45V. assigned at l- to 2-. This reduction shows a return wave whose position varies from 0.88V to -0.47V as the scan rate varies born 1OmVJs to SOOmV/s. The electrochemical properties of 3 have yet to be fully studied in addition to a more thorough investigation of the processes occurring for 2. A charge transfer complex of approximate stoichiometry [BEDT‘ITfl[Ni(diod& has been prepared by electrocrystallisation of a solution of TBA[Ni(diod,)] and BEDT-TTF in CH,CN/CHCl#ZH,C1(3/1). Conductivity studies on a compressed pellet ,gave a room temperature conductivity of l@*Scm-’ and exhibited semi-conductor behaviour over the temperature range 300 to 150K. with a band gap of -0.23eV. Attempts to prepare partially oxidised salts of [Ni(diod)J’ with [TMA]’ or [TBA]’ as counterion by electroocrystallisation have as yet led only to formation of the neutral complex [Ni(diod)d. Conclusions We have established
a convenient
synthesis
for a new class of
metal bis-1,2-dithiolate complexes and character&d the Ni. Cu and Au complexes. Initial conductivity measurements have given a relatively high room temperature conductivity of lo‘* Scm-’ for the compressed pellets of the charge transfer complex [BEDTTTF][Ni(diod)&. Future work will involve the preparation of diod complexes of other metals e.g. Pd, Pt or Fe, and the continued use of these complexes in the search for synthetic metals. Acknowledgements We would like to thank the S.E.R.C. for financial support. References 1.
P. Cassoux, L. Valade, H. Kobayashi. R. A. Clark, A. E. Underhill, Coord. Chem. Rev., 11.0 (1990) 115160.
2.
H. Miiller, Y. Ueba, Bull. Chem. Sot. Jpn., 66 (1993) 1773.
3.
N. Robertson, D. L. Parkin. A. E. Underhill. M. B. Hursthouse, K. M. A. Malik, /. Mater. Chem., Submitted for publication.
4.
C. T. Vance., R. D. Bereman, J.. Bordner, W. E. Hatfield, H. Helms, Irwrg. Chem., 24 (1985) 2905.
5.
C. S. Winter, S. N. Oliver, R. J. Manning, J. D. Rush, C. A. S. Hill, A. E. Underhill, J. Mater. Chem., 2 (1992) 443.
Synthetic
Synthesis,
Structure
Metals
and Properties
A E Underhill, University
71 (1995) 1955-1956
N Robertson
of [M(diod),]“‘ Complexes and D L Parkin
of Wales, Bangor, Gwynedd, LL57 2UW, UK
Abstract Complexes structurally
of the type [TBA][M(diod)J (M = Ni, Cu. Au; diod = 1,4dithia-6-oxa-2.3dithiolate) have been prepared and character&d and spectroscopically. The potential applications of these complexes to the synthesis of highly conducting materials is
discussed. Introduction Metal bis 1.2~dithiolate complexes have been widely studied due to their potential applications in the development of new electrical conductors and superconductors’. The potential to develop materials with improved properties compared with metal dmit complexes has encouraged the preparation of structurally related compounds. Results
and Discussion
We have prepared the complexes [TBA][M(diod)J [M = Ni(l), Cu(2), AU(~)] by the method outlined in scheme 1. The structure of these complexes is analogous to the previously reported organic donor OTT (BOBMT-TTF)*.
chloride gave an immediate precipitate of the product as a brown powder, soluble in polar solvents. The gold complex proved difficult to recrystallise due to the extremely fine nature of the precipitate and was therefore more readily isolated as the tetraphenylphosphonium (TPP) salt. A by-product of the reaction was the insoluble netural complex [M(diod)J. These could also be prepared from the anionic complexes by oxidation with I, in acetone. The complex salts however are of greater importance as precursors for synthetic metals because of their superior solubility and the possibility of converting them to a partially oxidised conducting salt. The crystal structure of l3 shows the structure around the NiS,C,S, core typical for this class of compounds’. Bond lengths lie between values for single and double bonds indicating the delocalised nature of the bonding. The anions adopt a chair conformation with respect to the -CH,-0-CH,-endgroups and form stacks with an intermolecular distance of 8.5A. The large intermolecular separation precludes any intermolecular interaction and this is reflected in the magnetic properties of the complex. Over the temperature range S-290K 1 obeys the CurieWeiss law with 8 approximately equal to zero and with one unpaired electron per molecular unit. Thus the complex exhibited paramagnetic behaviour with no indication of interaction between adjacent spins.
Scheme 1
The thione, obtained in 60% yield from [TEAJ,[Zn(dmit)J. was treated with NaOEt to afford the b&odium salt of the ligand 1.4dithia-6-Ooxa-2,3dithiolat (diod). Addition of the counterion [TBA]’ followed by slow addition of the appropriate metal
0379-6779/95/$09.50 0 1995 Elsevier SSDI 0379-6779(94)03124-O
Science
S.A. All rights
reserved
Complex 1 displays an intense absorption at 940 nm corresponding to the 2b,, to 34 transition observed in monoanion dithiolate?. This band remains unchanged in the solid state reflectance spectrum again indicating no interaction between molecules in the solid state. The presence of this band and a corresponding band at 905 nm for the neutral complex Ni(diod), suggests that these may have applications as a resonance The copper and gold enhanced non-linear optical material. monoanion complexes, with complete occupation of the HOMO and different orbital energies do not display a m-responding transition.
1956
A.E.
Underhill et al. I Synthetic Metals 71 (1995) 1955-1956
Structure
of lTBAI[Ni(diod)J
Complexes 2 and 3 show ‘H nmr signals for the ligand protons at 5.02 and 4.95 ppm respectively. The observation of these signals is in keeping with the expected diamagnetic nature of these complexes. Cyclic voltammetry studies have been carried out in CH,CN against SCE. Complex 1 shows two reversible waves at -0.65V and +0.28V assigned to 2-/l- and l-/O couples respectively. A further irreversible oxidation at +l.l6V was observed which could correspond to the formation of a cationic species. The copper complex 2 shows an irreversible oxidation at +0.56V, assigned as 1- to neunal, and a reduction at -1.45V. assigned at l- to 2-. This reduction shows a return wave whose position varies from 0.88V to -0.47V as the scan rate varies born 1OmVJs to SOOmV/s. The electrochemical properties of 3 have yet to be fully studied in addition to a more thorough investigation of the processes occurring for 2. A charge transfer complex of approximate stoichiometry [BEDT‘ITfl[Ni(diod& has been prepared by electrocrystallisation of a solution of TBA[Ni(diod,)] and BEDT-TTF in CH,CN/CHCl#ZH,C1(3/1). Conductivity studies on a compressed pellet ,gave a room temperature conductivity of l@*Scm-’ and exhibited semi-conductor behaviour over the temperature range 300 to 150K. with a band gap of -0.23eV. Attempts to prepare partially oxidised salts of [Ni(diod)J’ with [TMA]’ or [TBA]’ as counterion by electroocrystallisation have as yet led only to formation of the neutral complex [Ni(diod)d. Conclusions We have established
a convenient
synthesis
for a new class of
metal bis-1,2-dithiolate complexes and character&d the Ni. Cu and Au complexes. Initial conductivity measurements have given a relatively high room temperature conductivity of lo‘* Scm-’ for the compressed pellets of the charge transfer complex [BEDTTTF][Ni(diod)&. Future work will involve the preparation of diod complexes of other metals e.g. Pd, Pt or Fe, and the continued use of these complexes in the search for synthetic metals. Acknowledgements We would like to thank the S.E.R.C. for financial support. References 1.
P. Cassoux, L. Valade, H. Kobayashi. R. A. Clark, A. E. Underhill, Coord. Chem. Rev., 11.0 (1990) 115160.
2.
H. Miiller, Y. Ueba, Bull. Chem. Sot. Jpn., 66 (1993) 1773.
3.
N. Robertson, D. L. Parkin. A. E. Underhill. M. B. Hursthouse, K. M. A. Malik, /. Mater. Chem., Submitted for publication.
4.
C. T. Vance., R. D. Bereman, J.. Bordner, W. E. Hatfield, H. Helms, Irwrg. Chem., 24 (1985) 2905.
5.
C. S. Winter, S. N. Oliver, R. J. Manning, J. D. Rush, C. A. S. Hill, A. E. Underhill, J. Mater. Chem., 2 (1992) 443.