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