Crystal Structure and Magnetism of a Well Isolated 2D-Quantum Heisenberg Antiferromagnet, (Quinolinium)₂CuBr₄·2H₂O, and Its Anhydrous Form

Reaction of quinoline with HBr and CuBr2 generates a mixture of two compounds, (quinolinium)2CuBr4·2H2O (1) and (quinolinium)2CuBr4 (2) for which single-crystal X-ray structures have been solved. Compound 1 crystallizes in the monoclinic space group C2/c as layers of tetrabromocuprate ions which are separated by intervening layers of quinolinium ions. Compound 2 crystallizes in the triclinic space group P1̅. Magnetic data analysis reveals that 1 behaves as a 2D-quantum Heisenberg antiferromagnet with 2J/kB = −6.17(3) K within the layers. High field magnetization data at low temperatures suggests that TN must be less than 1.8 K for 1, yielding a figure of merit |kBTN/2J| < 0.29, which indicates excellent isolation between the layers. Magnetic exchange in compound 2 was much weaker and was fit to a linear chain antiferromagnet with 2J/kB = −1.59(3) K.