A metal complex and its use for binding or cleaving a nucleic acid. The metal complex has the formula: M is Pt, Pd, Ni, Co, or Cu; X is aryl, heteroaryl, cyclyl, or heterocyclyl; Y is halogen, tosylate, mesylate, triflate, pyrophosphate, or carboxylate; each of A1 and A2, independently, is N or C; each of A3 and A4, independently, is N, S, or 0, wherein A1, A2, A3, and A4 taken together have one positive charge; and each of R1 and R2, independently, is alkyl, aryl, heteroaryl, alkoxyl, aryloxyl, heteroaryloxyl, alkoxylcarbonyl, aryloxylcarbonyl, or heteroaryloxylcarbonyl.