Radical cation salts of BETS and ET with dicyanamidocuprate anions demonstrating metal-insulator and semiconductor–semiconductor transitions. (1st October 2020)

• Record Type: Journal Article
• Authors: Kushch, Nataliya D.; Kopotkov, Vyacheslav A.; Shilov, Gennady V.; Akimov, Alexander V.; Tokarev, Sergey V.; Yagubskii, Eduard B.; Zverev, Vladimir N.; Khasanov, Salavat S.; Winter, Stephen M.; Jeschke, Harald O.
• Is Part Of: Polyhedron. Volume 189(2020)
• Publication Date: 2020-10-01
• Subjects: Radical cation salt -- Dicyanamidocuprate -- Conductivity -- Crystal and electronic structure -- Pressure effect -- Phase transition; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2020.114705
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: The first radical cation salts based on BETS and ET π-donors with dicyanamide-cuprate counterions were synthesized. Their crystal and electronic structures as well as transport and magnetic properties were studied. Highlights: First radical cation salts with paramagnetic dicyanamidocuprate (Cu 2+ and Cu 1+, Cu 2+ ) anions. Semiconductor – semiconductor phase transition with a large hysteresis. Effect of pressure on metal-insulator and semiconductor-semiconductor transitions. First order phase transition associated with charge distribution. Abstract: Electrocrystallization of bis(ethylenedithio)tetraselenafulvalene (BETS) and bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of an electrolyte (Ph4 P)[Cu(dca)]3 ⋅H2 O [(dca) = N(CN)2 ] has been studied using different solvents. A new organic metal (BETS)2 Cu(dca)3 (1 ), and the first radical cation salt with 3D dicyanamidocuprate anion, incorporating both diamagnetic Cu 1+ and paramagnetic Cu 2+ atoms, (ET)2 Cu1.8 (dca)4 (2 ) have been obtained. Crystal structure, conducting properties of both salts, as well as the electronic structure of 2 and its structural analog (ET)2 CuMn(dca)4 (3 ) were analysed. The salts 1 and 2 have layered structures. In contrast to the BETS radical cation salt 1, complex 2 is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. At ambient pressure, the resistance of the crystals 1 shows semimetal behaviour down to 30 K. Below 30 K, the resistance sharply increases and the sample becomes insulating. The application of a pressure of about 3 kbar suppresses the metal-insulator transition. The salt 2 undergoes a semiconductor I - semiconductor II phase transition, which is manifested by a jump in the resistance and a hysteresis in the R(T) curves in a very large temperature range (185 – 250 K). The phase transition is accompanied by changes in the charge state of the ET molecules, and notable structure changes in the anion layer, especially in the environment of Cu 2+ . For the salt 3 the calculated selfconsistent charges show upon cooling a sharp increase of charge order between 291 K and 285 K.