Synthesis, Structure and Physical Properties of an Hybrid Compound Based on Strandberg Type Polyoxoanions and Copper Cations

Single crystals of novel Strandberg type molybdophosphonate complex, (C 5 H 7 N 2 ) 6 [Cu(H 2 O) 3 HP 2 Mo 5 O 23 ] 2 ·4H 2 O, are synthesized in aqueous solution and characterized by X-ray diffraction, spectroscopy (diffuse reflectance, UV–Vis and IR) and thermal analysis. Single crystal X-ray diffraction analysis reveals that this novel compound is composed of [Cu(H 2 O) 3 HP 2 Mo 5 O 23 ] 3− anions, three distinct 2-aminopyridinium cations as counter-ions and two distinct crystallization water molecules. The crystal packing is stabilized by H-bonds and π–π interactions, resulting in a 3D framework. In addition, the magnetic behavior of the related compound is measured. Magnetic measurements from 100 to 2 K indicate the presence of an antiferromagnetic coupling between the Cu (II) ions in (C 5 H 7 N 2 ) 6 [Cu(H 2 O) 3 HP 2 Mo 5 O 23 ] 2 ·4H 2 O complex, resulting in a maximum of an antiferromagnetic–paramagnetic transition at T N = 7 K. Magnetic susceptibility data indicate an antiferromagnetic Curie–Weiss behavior in the studied temperature range, and molecular field theory gives the (J/k B ) values of the nearest neighbor interactions between copper ions.