Gold and Nickel Extended Thiophenic-TTF Bisdithiolene Complexes.

Rafaela Silva,Sandra Rabaça,Laura Pereira,Isabel Santos,Elsa Lopes,Manuel Almeida,Bruno Vieira,Marta Andrade,Joana Coutinho,Dulce Belo

doi:10.3390/molecules23020424

Abstract

Gold and nickel bisdithiolene complexes with methyl and tert-butyl substituted thiophenetetrathiafulavalenedithiolate ligands (α-mtdt and α-tbtdt) were prepared and characterized. These complexes were obtained, under anaerobic conditions, as tetrabutylammonium salts. The diamagnetic gold monoanion (n-Bu4N)[Au(α-mtdt)2] (3) and nickel dianionic species (n-Bu4N)x[Ni(α-mtdt)2] (x = 1,2) (4) were similar to the related non-substituted extended thiophenic-TTF (TTF = tetrathiafulvalene) bisdithiolenes. However the introduction of the large, bulky substituent tert-butyl, led to the formation of a Au (I) dinuclear complex, (n-Bu4N)2[Au2(α-tbtdt)2] (5). The neutral methyl substituted gold and nickel complexes were easily obtained through air or iodine exposure as polycrystalline or amorphous fine powder. [Au(α-mtdt)2] (6) and [Ni(α-mtdt)2] (7) polycrystalline samples display properties of a metallic system with a room temperature electrical conductivity of 0.32 S/cm and ≈4 S/cm and a thermoelectric power of ≈5 µV/K and ≈32 µV/K, respectively. While [Au(α-mtdt)2] (6) presented a Pauli-like magnetic susceptibility typical of conducting systems, in [Ni(α-mtdt)2] (7) large magnetic susceptibilities indicative of high spin states were observed. Both electric transport properties and magnetic properties for gold and nickel [M(α-mtdt)2] are indicative that these compounds are single component molecular conductors.

Highlights

High electrical conductivity and properties typical of a metal in a compound based on a neutral molecular species were initially reported by our group in the neutral gold complex [Au(α-tpdt)2 ](α-tpdt = 2,3-thiophenedithiolate) (Scheme 1) [1] and was soon followed by [Ni(tmdt)2 ] (Scheme 1), an extended TTF-bisdithiolene type of complex, reported by A
The TTF donors non-symmetrically fused with substituted thiophene moeieties 1 and 2, that have been recently reported by us [20], are employed here as potential ligand precursors for the formation of extended transition metal bisdithiolenes
The tetrabutylammonium salt of the monoanionic gold complex 5 presented a higher solubility than related unsubstituted compounds, the attempt to prepare the transition metal complex lead instead to a Au(I) complex, (n-Bu4 N)2 [Au2 (α-tbtdt)2 ]

Summary

Introduction

[Au(α-tpdt)2 ] presented a room temperature electrical conductivity of σRT = 7 S/cm as a polycrystalline sample while single crystals of [Ni(tmdt)2 ] presented σRT = 400 S/cm [1,2,3] These neutral complexes enabled the establishment of a new paradigm of molecular conductors where free carriers and metallic properties can be generated in molecular compounds based on a neutral single-component by a mechanism characteristic of semi-metals. The requirements for such properties were soon established as a small HOMO-LUMO energy gap and strong 3D intermolecular interactions [4,5,6].

Methods

Results

Conclusion