Structural, Electrical, and Magnetic Versatility of the Oxalate-Based [CuFe] Compounds Containing 2,2':6',2″-Terpyridine: Anion-Directed Synthesis.

The heterodimetallic [CuFe] compounds [Cu(terpy)Cl][Fe(CO)]·10HO (;terpy = 2,2':6',2''-terpyridine), [Cu(HO)(terpy)(CO)][CuFe(CHOH)(terpy)(CO)] (), and {[CuFe(HO)(terpy)(CO)]·6HO} () were obtained using building block approach, from reaction of aqueous solution of [Fe(CO)] and a methanol solution containing Cu ions and terpy by the layering technique. Interestingly, by changing only the anion of the starting salt of copper(II), Cu(NO)·3HO instead of CuCl·2HO, an unexpected change in the type of bridge, oxalate ( and ) versus chloride (), was achieved, thus affecting the overall structural architecture. Two polymorphs of 3D coordination polymer [CuFe(HO)(terpy)(CO)] (), crystallizing in the triclinic () and monoclinic () space groups, were formed hydrothermally, depending on whether CuCl·2HO or Cu(NO)·3HO was added to the water, besides K[Fe(CO)]·3HO and terpy, respectively. Under hydrothermal conditions iron(III) from initial building block is reduced to the divalent state, creating 2D honeycomb [Fe(CO)] layers, which are bridged by [Cu(HO)(terpy)] cations. Compounds were investigated by single-crystal X-ray diffraction, IR, and impedance spectroscopies, magnetization measurements, and density functional theory (DFT) calculations. In compounds and , 0D magnetism is observed, with having a ground-state spin of 1 due to different interactions through chloride bridges of Cu ions in tetramer [Cu(terpy)Cl] and showing strong antiferromagnetic coupling of Cu ions mediated by oxalate ligand in [Cu(HO)(terpy)(CO)] and weak ones between Cu and Fe ions through oxalate bridge in [CuFe(CHOH)(terpy)(CO)]. Polymer exhibits antiferromagnetic phase transition at 25 K: The [Fe(CO)] layers are antiferromagnetically ordered, and a small amount of interlayer interaction is transferred through [Cu(HO)(terpy)] cations via O-Cu-O bridges. Additionally, compounds and are electrical insulators, while and show proton conductivity.