Crystal Structures and Magnetic Properties of a Novel Layer Perovskite System: (3-Picoliniumylammonium)CuX4 (X = Cl, Br)
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- 作者：Greg S. Long ; Mingyi Wei ; and Roger D. Willett
- 刊名：Inorganic Chemistry
- 出版年：1997
- 出版时间：July 2, 1997
- 年：1997
- 卷：36
- 期：14
- 页码：3102 - 3107
- 全文大小：197K
- 年卷期：v.36,no.14(July 2, 1997)
- ISSN：1520-510X
文摘
The compounds(C6N2H10)CuX4,where the cation is diprotonated 3-picolylamine and X =Cl- or Br-, form anunusual variant of the normal antiferrodistortiveA2CuX4 lattice[(C6N2H10)CuCl4,orthorhombic, Pna21, a=7.747(1), b = 24.960(2), and c =17.041(1) Å, Z = 12;(C6N2H10)CuBr4,orthorhombic, Pna21, a =8.133(1), b= 26.129(1), and c = 17.148(1) Å,Z = 12]. The structures contain ribbons of theantiferrodistortive sheetswhich are six copper atoms wide. The central four Cu(II) ionshave the usual elongated octahedral coordination,while on each edge are CuX42-ions which have a distorted tetrahedral geometry. LongCu···X interactions(4.000 and 4.124 Å for the Cl and Br salts, respectively) betweenthese terminating anions link the ribbons togetherinto sheets. The organic cations provide overall stability to thelattice and link adjacent sheets together, forcingthe existence of short two-halide X···X contacts between sheets(average Cl···Cl = 4.629 Å, Br···Br = 4.425Å).While the changes in the semicoordinate Cu···X distancesupon replacement of Cl by Br mirror the change inionic radius, the X···X distances actually decrease when thelarger bromide ion is introduced. This is becausethese distances are largely dictated by the size of the organic cation.The magnetic data for both salts show thepresence of predominant ferromagnetic interactions at high temperature.The Cl salt orders antiferromagneticallyat Tc = 5.7 K, and the susceptibility data canbe fit to a S = 1/2 Heisenbergmodel for antiferromagneticallycoupled ferromagnetic layers with a mean in-plane exchange constant ofJ/k = 8.13 K and an interlayerexchangeconstant of J'/k = 1.22 K. Thecorresponding values for the Br salt are Tc =18.9 K, J/k = 21.3 K, andJ'/k =5.87 K The increase in magnitude of the exchange constants and orderingtemperature of the Br salt relative tothe Cl salt is consistent with the increase in ionic radius ofBr- relative to Cl-.