Coordination chemistry of verdazyl radicals:: Group 12 metal (Zn, Cd, Hg) complexes of 1,4,5,6-tetrahydro-2,4-dimethyl-6-(2′-pyridyl)-1,2,4,5-tetrazin-3(2H)-one (pvdH3) and 1,5-dimethyl-3-(2′-pyridyl)-6-oxoverdazyl (pvd)

Ferricyanide oxidation of 1,4,5,6-tetrahydro-2,4-dimethyl-6-(2'-pyridyl)-1,2,4,5-tetrazin-3(2H)-one (pvdH3) produces the stable chelating free radical 1,5-dimethyl-3-(2'-pyridyl)-6-oxoverdazyl (pvd) as an orange solid. Combination of group 12 metal halides with the ligand pvdH3 in acetonitrile results in precipitation of metal complexes. The mercuric chloride complex crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 8.5768(8) Å, b = 19.1718(17) Å, c = 8.5956(8) Å, β = 90.405°, and V = 1413.4(2) Å3. The mercuric ion is tricoordinate with a distorted trigonal planar geometry. Cadmium iodide and zinc chloride induce ring opening of the tetrazine resulting in pentacoordinate complexes of a hydrazone ligand. The cadmium iodide complex crystallizes in the triclinic space group P1 with cell dimensions a = 7.7184(8) Å, b = 8.0240(9) Å, c = 13.348(2) Å, α = 97.876(4)°, β = 95.594(6)°, γ = 107.304(6)°, and V= 773.40(21) Å3. Oxidation of all three metal complexes produces verdazyl radicals. Metal coordination is indicated by small changes in the EPR spectrum and by changes in the UV-visible spectrum, in particular the changes in the position of bands in the visible region. The metal halide-pvd complexes can also be synthesized by direct combination of metal halides with the free radical.