First Example of a CuII Polymeric Complex Having a Tetranuclear Repeating Unit with a S = 2 Ground State. Crystal Structure of [Cu4(dpk·CH3O)2Cl6]n (dpk·CH3OH = Unimethylated Diol of Di-2-pyridyl Ketone)

The synthesis, crystal structure and properties of the compound [Cu 4 (dpk·CH 3 O) 2 Cl 6 ] n (dpk·CH 3 OH = unimethylated diol of di-2-pyridyl ketone) ( 1 ), the first example of a copper(II) polymer having a tetrameric repeating unit with S = 2 ground state is reported. The synthesis of compound 1 has been achieved via the reaction of CuCl 2 with dpk in methanol. The base-catalyzed addition results in the formation of a unimethylated diol which may deprotonated. Crystal structure data: [C 12 H 11 N 2 O 2 Cl 3 Cu 2 ], M r = 448.68; triclinic; space group P1̄; a = 7.800(1) (Å); b = 8.946(1) (Å); c = 13.383(1) (Å); α = 118.964(3)°; β = 92.693(3)°; γ = 66.824(3)°; Z = 2. Variable temperature magnetic susceptibility measurements indicate the presence of a ferromagnetic behavior with antiferromagnetic coupling below 15 K. The best fit parameters obtained from this model are J 1 = 71.32 cm - 1, J 2 = 1.43 cm - 1, J 3 = 0.07 cm - 1, J 4 = 0 (fixed), zJ = −0.553 cm - 1, and g = 2.1 (fixed). The energy levels obtained from the fitting procedure show a S = 2 ground state. The polycrystalline powder EPR spectra at 4.1 K, show an intense broad signal spread over 3900 G with g = 2.34, indicative of a bulk concentration of copper ions having strong ferromagnetic interaction.