A metal complex and its use for binding or cleaving a nucleic acid. The metal complex has the formula: ##STR1## 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 A.sub.1 and A.sub.2, independently, is N or C; each of A.sub.3 and A.sub.4, independently, is N, S, or 0, wherein A.sub.1, A.sub.2, A.sub.3, and A.sub.4 taken together have one positive charge; and each of R.sub.1 and R.sub.2, in...