New Family of Six Stable Metals with a Nearly Isotropic Triangular Lattice of Organic Radical Cations and Diluted Paramagnetic System of Anions: κ(κ⊿/sub>)-(BDH-TTP)4MX4·Solv, where M = CoII, MnII; X = Cl, Br, and Solv = (H2O)5, (CH2X2)

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• 作者：Andrey A. Bardin ; Hiroki Akutsu ; Jun-ichi Yamada
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：March 2, 2016
• 年：2016
• 卷：16
• 期：3
• 页码：1228-1246
• 全文大小：1110K
• ISSN：1528-7505

文摘

A new family of six paramagnetic metals, namely, κ-(BDH-TTP)₄CoCl₄·(H₂O)₅ (I), κ-(BDH-TTP)₄Co_0.54Mn_0.46Cl₄·(H₂O)₅ (II), κ-(BDH-TTP)₄MnCl₄·(H₂O)₅ (III), κ_⊥-(BDH-TTP)₄CoBr₄·(CH₂Cl₂) (IV), κ_⊥-(BDH-TTP)₄MnBr₄·(CH₂Cl₂) (V), and κ_⊥-(BDH-TTP)₄MnBr₄·(CH₂Br₂) (VI), has been synthesized and characterized by X-ray crystallography, four-probe conductivity measurements, SQUID magnetometry, and calculations of electronic structure. The newly discovered κ_⊥-type packing motif of organic layers differs from the parent κ-type by a series of longitudinal shifts of BDH-TTP radical cations in the crystal structure. Salts I–VI form two isostructural groups: I–III (κ) and IV–VI (κ_⊥). Salts I–III are isostructural to the previously discovered κ-(BDH-TTP)₂Fe^IIIX₄ (X = Cl, Br) even though the charge of FeX₄^– anions is half that of the MX₄^2– (M = Co, Mn) anions. The tetrahedral anions are disordered in I–III but completely ordered in IV–VI. The type of included solvent molecule is solely determined by the anion size. The paramagnetic subsystem is effectively spin diluted either by anion disorder (I–III) or by spatial separation (IV–VI). The Weiss constants are virtually zero for all compounds (e.g., θ(III) = 0.0056 K, θ(V) = −0.076 K). Curie constants are dominated by anion paramagnetic centers indicating high spin states 5/2 for Mn^II and 3/2 for Co^II with large spin–orbital coupling. All compounds retain metallic properties down to 4.2 K. There is a magnetic breakdown gap of width (w) in the chiral salts IV–VI: w(IV) > w(V) ≈ w(VI) but no gap in the centrosymmetric salts I–III. Electronic structure calculations at room temperature revealed a nearly isotropic triangular lattice in I–III and a honeycomb lattice in IV–VI with an extreme geometric spin frustration exceeding the level reported for the quantum “spin liquid” κ-(BEDT-TTF)₂Cu₂(CN)₃.