High Thermal Durability of Water-Free Copper-Octacyanotungsten-Based Magnets Containing Halogen Bonds

Two-dimensional (2-D) cyano-bridged Cu–W bimetallic assemblies that include halogen-substituted pyridine molecules, [CuII(3-iodopyridine)4][CuII(3-iodopyridine)2]2[WV(CN)8]2 (1) (triclinic crystal structure, P1̅ space group), [CuII(3-bromopyridine)4][CuII(3-bromopyridine)2]2[WV(CN)8]2 (2) (triclinic, P1̅), and [CuII(3-chloropyridine)2(H2O)2][CuII(3-chloropyridine)2]2[WV(CN)8]2·4H2O (3) (monoclinic, P21/c), were synthesized. Thermogravimetric measurements demonstrate that 1 and 2 have high thermal durability up to ca. 150 °C (423 K) due to the lack of water molecules in the crystal and the stacked Cu–W 2-D layers with halogen bonding between halogen-substituted pyridine and the cyano nitrogen of octacyanotungstate. In contrast, 3 exhibits weight loss above ca. 50 °C (323 K) as the water molecules between the 2-D layers are removed upon heating. Magnetic measurements show that 1–3 are ferromagnets due to parallel ordering of the magnetic spins on CuII (S = 1/2) and WV (S = 1/2) with Curie temperatures (TC) of 4.7 K (1), 5.2 K (2), and 7.2 K (3).