Studies on binuclear complexes. Synthesis and catalytic behaviour of Fe-M complexes (M Mo, Ni, Rh, Cu, Hg) using trans- Fe(Ph2Ppy)2(CO)3 [Ph2Ppy = 2-(diphenylphosphino) pyridine] as a neutral tridentate ligand. Molecular structure of FeHg(μ-Ph2Ppy)2(CO)3(SCN)2