Straight linear tetranuclear complexes have been prepared by using pyphos ligand (pyphos = 6-diphenylphosphino-2-pyridonate), which has unique coordinating sites comprised of three kinds of elements, i.e., phosphine, nitrogen, and oxygen atoms, in almost linear fashion. The starting complex is the quadruply bonded dinuclear molybdenum(II) complex, Mo-2(pyphos)(4) (1), which was prepared by the reaction of Mo-2(OAc)4 with sodium salt of pyphos. Single crystal X-ray analysis revealed that 1 consists of quadruply-bonded Mo-2 and trans-arranged diphosphine at both axial position of Mo-2 core. Thus, transition metal can be expected to be placed at both axial positions of Mo-2 core. Thus, treatment of 1 with Pd(II) and Pt(II) complexes gave rise to tetranuclear complexes of the general formula, Mo(2)Pd(2)X(4)(pyphos)(4) (2) and Mo(2)Pt(2)X(4)(pyphos)(4) (4) (a : X = Cl; b : X = Br; c : X = I).