XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O C 06
Electrocrystallisation of (Perylene) 2 [M(mnt) 2 ] salts
Mónica Afonso, 1 Manuel J. Matos, 2,3 Rafaela A. L. Silva, 1 Quirina Ferreira, 2
Manuel Almeida 1
1 Dept. Chemistry, ITN / CFMCUL Estrada Nacional 10, P-2686-953 Sacavém, Portugal
2
IT, Av. Rovisco Pais, 1049-001 Lisboa, Portugal,
3 ISEL, Av. Emídio Navarro, 1959-007 Lisboa, Portugal
mafonso@itn.pt
The charge transfer salts based on perylene (Per) and transition metal
bis-maleonitrile-dithiolate M(mnt) 2 with different transition metals M and general
formula, (Per) 2 [M(mnt) 2 ] have attracted continued interest for more than 30 years due to
unique properties derived from the existence in the same solid of two types of chains:
conducting chains of partially oxidized perylene molecules (Per) 1/2+ and chains of
monoanionic complexes [M(mnt) 2 ] - that depending on the metal can be either
diamagnetic (M=Cu, Au, Co) or paramagnetic (M=Ni, Pd, Pt, Fe). The mutual
interaction between the two type of chains, both subject to lattice instabilities typical of
one-dimensional conducting and magnetic systems, leads to a very rich and
unprecedented variety of physical phenomena [1,2]. However the study of these
compounds has been always limited by difficulties in the growth of good quality single
crystals. The situation is further complicated by the fact that the crystals can be obtained
in two polymorphs, e.g. in M=Cu, Ni [3] and Pt [4] and different stoichiometries are
possible for M=Co [1].
These salts have been obtained mainly by electrocrystallisation; a solution of perylene
and salts of [M(mnt) 2 ] - is submitted to electrochemical oxidation which generates
perylene cations to give insoluble crystals of the (Perylene) 2 M(mnt) 2 compounds
growing on the anode. This electrochemical method has advantages over chemical
oxidation routes yielding better quality crystals, but has also strong limitations.
In this communication we report the results of our systematic investigation aiming at to
establish the best conditions for the growth of single crystals of the (Per) 2 M(mnt) 2
compounds by electrocrystallisation that is constrained by the rather low solubility of
perylene in appropriated solvents and the instability of the perylene radical cation. The
conditions which allowed for the first time the preparation of (Per) 2 [Pd(mnt) 2 ] by
electrocrystallisation are described. AFM and STM microscopy were used to monitor
the early stages of crystal growth on different electrodes. The nucleation is found to
occur preferentially at edge dislocations of HOPG and to be oriented along Au and Pt
crystallographic axis.
Acknowledgments: Work supported by F CT under contract PTDC/QUI-QUI/101788/2008.
References
[1] Almeida M. and Henriques R. T., in Organic Conductive Molecules and Polymers, H. S. Nalwa
ed., vol. 1, chapter 2, pp. 87-149, John Wiley 1997.
[2] Brooks, J.S., Graf, E.S.; Almeida, M.; R.T.; Matos, M. et al.; J. Low Temp. Phys., 2006, 142, 787.
[3] Gama, V.; Almeida, M.; Henriques, R.T.; Santos, I.C.; et al. J. Phys. Chem., 1991, 95, 4263.
[4] Henriques, R.T.; Sousa, I.; Almeida, M.; et al.; J. Low Temp. Physics, 2006, 142, 405.
September, 811, 2010. ISEL - Lisbon 45