New Mononuclear, Cyclic Tetranuclear, and 1-D Helical-Chain Cu(II) Complexes Formed by Metal-Assisted Hydrolysis of 3,6-Di-2-pyridyl-1,2,4,5-tetrazine (DPTZ): Crystal Structures and Magnetic Properties

The reactions of 3,6-di-2-pyridyl-1,2,4,5-tetrazine (DPTZ) with different CuII salts generate two new ligands, 2,5-bis(2-pyridyl)-1,3,4-oxodiazole (L1) and N,N‘-bis(α-hydroxyl-2-pyridyl)ketazine (H2L2), from the metal-assisted hydrolysis
of DPTZ, and form three new complexes:  a mononuclear complex [Cu(L1)2(H2O)2]·2ClO4 (1), a linear coordination
polymer [Cu(L1)(NO3)2]8 (2), and a cyclic tetranuclear complex [Cu4(L2)2(Im)2(NO3)4(H2O)2] (3) (Im = imidazole).
Crystal data for 1:  space group P21/n with a = 10.339(3) Å, b = 10.974(2) Å, c = 13.618(4) Å, β = 103.24(1)°,
and Z = 2. Crystal data for 2:  space group C2/c with a = 13.9299(14) Å, b = 9.2275(9) Å, c = 12.1865(13) Å,
β = 111.248(2)°, and Z = 4. Crystal data for 3:  space group P21/n with a = 9.3422(14) Å, b = 15.987(2) Å, c
= 13.963(2) Å, β = 108.587(3)°, and Z = 2. L1 acts as a bidentate chelating ligand in 1 and as a bis-bidentate
chelating ligand in 2 with the shortest intramolecular Cu···Cu distance of 6.093 Å. L2 is a hexadentate ligand to
bridge four CuII ions, forming an interesting neutral cyclic tetranuclear complex 3 with Cu···Cu distances varying
from 4.484 to 9.370 Å. The mechanism of the metal assisted hydrolysis of DPTZ is discussed in detail. Magnetic
susceptibility measurements indicate that 2 shows weak ferromagnetic interaction (J = 2.85 cm-1) along the 1-D
helical chain, and that 3 displays weak antiferromagnetic interaction (J = −1.19 cm-1 for the NN bridge) and
ferromagnetic interaction (j = 0.11 cm-1 for the OCN bridge) between the adjacent CuII ions.