Complexes based on asymmetrically substituted pyridine–dithiolene ligands [M(4-pedt)2] (M = Au, Cu, Ni; 4-pedt = 1-(pyridin-4-yl)-ethylene-1,2-dithiolate): Synthesis, structure and physical properties
Graphical abstract
The synthesis of M(4-pedt)2 complexes of nickel, copper and gold obtained as tetrabutylammonium, tetraphenylphosphonium or sodium 18-crown-6 ether salts are described and these compounds are characterised by single-crystal X-ray diffraction, cyclic voltammetry, EPR and magnetic susceptibility measurements.
Introduction
Transition metal bis(dithiolene) complexes have attracted research attention for more than 30 years and, due to their rich redox behaviour and favourable solid state interactions in their square-planar geometry, they have been widely used in the preparation of conducting and magnetic materials [1]. These complexes can be seen as inorganic analogues of the corresponding TTF type donors where the transition metal replaces the central CC bond. The TTF type donors have been at the basis of the large majority of all known molecular conductors and superconductors, and these inorganic analogues offer the additional advantage that depending on the oxidation state and on the transition metal they can be either diamagnetic or paramagnetic with different magnetic moments.
Recently there has been an increasing focus of attention on the preparation of donors which, in addition to their electroactive role, can bind directly to transition metals and some TTF derivatives substituted with groups containing N coordinating atoms [2] and their complexes have been recently described [3]. The corresponding inorganic analogues, bis(dithiolene) complexes with ligands bearing nitrogen coordinating groups have been however a lot less explored. Having in mind such type of complexes, we recently focused our interest on bis(dithiolene) complexes based on thio-azo ligands bearing heterocyclic groups and recently described the first neutral Ni bis(dithiolene) complex (formally NiIV) with alkylpyridyl substituted ligands, Ni(dpesdt)2 (dpesdt = bis(2-pyridyletthylsulfanyl)-,2-dithiolate) [4].
Asymmetrically substituted dithiolenes have been significantly less studied in spite of providing also interesting properties [5] namely for magnetic materials [6] and optoelectronics [7]. One example of bis(dithiolene) complexes bearing heterocyclic groups are the M(n-pedt)2 complexes (n = 2, 3 or 4), based on the asymmetrically substituted ligand n-pedt = S–C(H)C(R)–S; R = 4-pyridyl. Ligand 4-pedt was previously presented in a preliminary short report [8]. More recently monoanionic gold bisdithiolene complexes with R = n-pyridyl ligands were also described [9].
In this paper, we describe the preparation and characterisation of monoanionic [M(4-pedt)2]− complexes of nickel, copper and gold obtained as tetrabutylammonium, tetraphenylphosphonium or sodium 18-crown-6 ether salts.
Section snippets
Materials and methods
All manipulations were carried out under anaerobic conditions, unless stated otherwise. Whenever required, the solvents were dried according to the standard literature procedures [10], freshly distilled, and saturated with nitrogen prior to use. All starting reagents were purchased from commercial sources and used without further purification or synthesised from published methods. The 4-(4-pyridyl)-1,3-dithiol-2-one was synthesised according to literature reports [8], [11].
Elemental analyses of
Synthesis
The synthesis of the nickel, copper and gold complexes 1–7 were performed following standard procedures for complexes with this type of dithiolene ligands (Scheme 1). The dithiolate ligand (L) was obtained from the corresponding oxo compound by hydrolytic cleavage with sodium methoxide and without intermediate isolation it was reacted with the selected metal salt to give an anionic complex which is precipitated as a salt in the presence of the selected cation. The presence of water was
Conclusion
The new paramagnetic complex, [Ni(4-pedt)2]−, with the dithio-azo 4-pedt ligand has been synthesised, and isolated as the [PPh4]+, [n-Bu4N]+ and Na+(18C6) salts, which were characterised by single crystal X-ray diffraction, cyclic voltametry EPR and magnetic susceptibility. These three compounds present three distinct crystal structures and similar magnetic and redox behaviour, characteristic of monoanionic Ni complexes with quadrangular coordinating geometry and exhibit two quasi reversible
Acknowledgements
This work was partially supported by FCT trough Contract (PTDC/QUI/64967/2006) and by GRICES-Ministère des Affaires Etrangères (France) Pessoa No. 07981RL bilateral agreement and it also benefited from the ESF COST action D35.
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2013, PolyhedronCitation Excerpt :Scheme 2, for example, demonstrates two nickel dithiolene complexes, in which cyano group substituted nickel complex exhibits absorption band at 863 nm and the phenyl substituted metal complex reveals electronic absorption band at 935 nm. This indicates that substituent on dithiolene moiety can influence in the shift of position of electronic absorption band of charge transfer transition, meaning thereby, electron-donating/electron-withdrawing substituents play an important role in the delocalization of the chelate ring in metal–bis(dithiolene) complexes [16–21]. These facts prompted us to design and synthesize new type of N-hetero substituent-based (pyridin-2-yl, pyridin-3-yl, thiophen-2-yl, furan-2-yl and naphthalen-2-yl) dithiolene ligands and to synthesize corresponding metal bis(dithiolene) complexes (PPh4)2[NiII(C8H2N2S2R2)2] (R = pyridin-2-yl (1), pyridin-3-yl (2), thiophen-2-yl (3), furan-2-yl (4)) and (PPh4)[NiIII(C8H2N2S2R2)2] (R = naphthalen-2-yl (5)), which enable us to compare the substituent effect on the redox potentials of the title complexes.
Neutral gold and nickel bis[1-(pyridin-4-yl)-ethylene-1,2-dithiolene] complexes: Synthesis, structure and physical properties
2012, PolyhedronCitation Excerpt :The paramagnetic contribution was obtained from experimental data after correction for the core diamagnetism, estimated from tabulated Pascal constants as 334 × 10−6 emu/mol and 706 × 10−6 emu/mol for [Au(4-pedt)](2) and [Au(4-pedt)2]2 NaPF6 (3) respectively. The monoanionic bis(dithiolene) complexes, [M(4-pedt)2]− M = Ni and Au, were synthesized under anaerobic conditions following previously described procedures [28]. As previously reported these monoanionic complexes [M(4-pedt)2] M = Ni and Au are easily oxidized just by air exposure upon recrystallisation.