Bulk and Molecular Compressibilities of Organic鈥揑norganic Hybrids [(CH3)4N]2MnX4 (X = Cl, Br); Role of Intermolecular Interactions

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• 作者：Jose Antonio Barreda-Arg眉eso ; Lucie Nataf ; Yamilet Rodr铆guez-Lazcano ; Fernando Aguado ; Jes煤s Gonz谩lez ; Rafael Valiente ; Fernando Rodr铆guez ; Heribert Wilhelm ; Andrew P. Jephcoat
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：October 6, 2014
• 年：2014
• 卷：53
• 期：19
• 页码：10708-10715
• 全文大小：475K
• ISSN：1520-510X

文摘

This work reports an X-ray diffraction, X-ray absorption, and Raman spectroscopy study of [(CH₃)₄N]₂MnX₄ (X = Cl, Br) under pressure. We show that both compounds share a similar phase diagram with pressure. A P2₁/c monoclinic structure describes precisely the [(CH₃)₄N]₂MnCl₄ crystal in the 0.1鈥? GPa range, prior to crystal decomposition and amorphization, while [(CH₃)₄N]₂MnBr₄ can be described by a Pmcn orthorhombic structure in its stability pressure range of 0鈥? GPa. These materials are attractive systems for pressure studies since they are readily compressible through the weak interaction between organic/inorganic [(CH₃)₄N⁺/MnX₄^{2鈥?/sup>] tetrahedra through hydrogen bonds and contrast with the small compressibility of both tetrahedra. Here we determine the equation-of-state (EOS) of each crystal and compare it with the corresponding local EOS of the MnX₄2鈥?/sup> and (CH₃)₄N+ tetrahedra, the compressibility of which is an order and 2 orders of magnitude smaller than the crystal compressibility, respectively, in both chloride and bromide. The variations of the Mn鈥揅l bond distance obtained by extended X-ray absorption fine structure and the frequency of the totally symmetric 谓₁(A₁) Raman mode of MnCl₄2鈥?/sup> with pressure in [(CH₃)₄N]₂MnCl₄ allowed us to determine the associated Gr眉neisen parameter (纬_loc = 1.15) and hence an accurate local EOS. On the basis of a local compressibility model, we obtained the Gr眉neisen parameters and corresponding variations of the intramolecular Mn鈥揃r and C鈥揘 bond distances of MnBr₄2鈥?/sup> (纬_loc = 1.45) and (CH₃)₄N+ (纬_loc = 3.0) in [(CH₃)₄N]₂MnBr₄.}