Partial Substitution of Ag(I) for Cu(I) in Quantum Spin Liquid κ-(ET)₂Cu₂(CN)₃, Where ET Is Bis(ethylenedithio)tetrathiafulvalene

Abstract

Three mixed crystals, κ-(ET)2Ag2x Cu2(1–x)(CN)3 [ET is bis­(ethylenedithio)­tetrathiafulvalene; 0.24 < x < 0.71] with a κ-type packing motif of face-to-face ET dimers, were obtained by electrocrystallization. Regardless of the composition, each ET dimer fits into a hexagonal anionic opening (i.e., key-on-hole packing) similar to its parent spin liquid candidate, κ-(ET)2Cu2(CN)3. X-ray diffraction and energy dispersive spectroscopy analyses revealed that Cu and Ag atoms are statistically disordered with a fairly homogeneous distribution in a crystal. A structural variation depending on x is responsible for the change in the calculated band parameters related to intermolecular interactions, electron correlations, and frustrations. A salt with nearly equimolar amounts of Ag and Cu (x = 0.49) is semiconductive at ambient pressure and undergoes a Mott transition upon application of hydrostatic pressure. Along with the positive pressure dependence of the transition temperature, the temperature-independent amplitude of magnetic torque at low temperatures suggests that the insulating phase is a quantum spin liquid. Further application of pressure results in the appearance of a superconducting phase. Contrary to those of the parent salts, κ-(ET)2Cu2(CN)3 and κ-(ET)2Ag2(CN)3, the transition temperature increases as the pressure increases and eventually reaches 4.5 K at 1.65 GPa.

Bis(ethylenedithio)tetrathiafulvalene Cation Radical Salts Composed of Nonuniform Silver(I) Complex Polyanions

“…Ion radical salts with t′/t > 1 are a research topic of great current interest, 50−53 because their electronic ground state remains far from consensus from both experimental and theoretical perspectives. It is noteworthy that the t′/t value of 2 greatly exceeds those of the reported κ-(ET) 2 X salts with t′/t > 1; 1.09 for X = Cu 2 (CN) 3 − (quantum spin liquid), 54 1.16 for Ag 0.98 Cu 1.02 (CN) 3 − (quantum spin liquid), 55 1.42 for X = B(CN) 4 − (valence bond crystal), 56 1.76 for X = TaF 6 − (quantum spin liquid), 57 and 1.79 for X = CF 3 SO 3 − (antiferromagnet). 58,59 Salt 2 also has a high σ RT value (10 S cm −1 ) and exhibits semiconducting behavior (E a = 0.10 eV) down to ca.…”

Organic quantum materials: A review

“…Furthermore, partial replacement of Cu by Ag atoms in κ‐CuCN realized a QSL state. Yoshida et al 204 developed three mixed compounds κ‐(ET) 2 Ag 2 x Cu 2(1– x ) (CN) 3 (0.24 < x < 0.71) and found their t '/ t values would increase with x . When x was 0.49, despite low geometrical frustration suggested by a t ′/ t value of 1.253, the compound (donated as κ‐AgCu) remained a magnetically disordered state down to 2 K, suggesting it was a promising QSL candidate.…”

Tuning Charge Order in (TMTTF)2X by Partial Anion Substitution

“…Physical pressure, on the other hand, enables tuning in arbitrary steps through the phase diagram, at the cost of more difficult experiments that have to be carried out in a pressure cell. The advantages of both approaches-flexible tuning and ambient pressure experiments-can be achieved by partial substitution of the constituents, either the donor molecules [16][17][18][19][20][21][22][23][24][25][26][27][28][29] or the anions [30][31][32][33], as depicted in Figure 1. So far, partial substitution has remained poorly investigated compared to pressure tuning, but, in addition to bandwidth tuning, it also enables the study of disorder effects on metal-insulator transitions and superconductivity [29].…”