Hydrothermal reactions of metal nitrates and ligand bis(5-(pyridine-2-yl)-1,2,4-triazol-3-yl)methane (H L ) gave three cluster compounds, {Cr }, {Zn } and {Fe }. Notably, methylene group of H L was in situ oxidized either to hydroxymethylated (L -O) in the metallo-ring {Zn } or to a rigid carbonylated (L =O) in the screw-type {Fe }. In light of comparative experimental results, NO was deduced to be of a catalytic role in the ligand oxidation. Metal ion could be regarded as an "induced" tool for clusters generation in self-assembly process.