The heteronuclear cluster chemistry of the group 1B metals. Part 10. Synthesis, structures, and dynamic behaviour of the bimetallic hexanuclear group 1B metal cluster compounds [M2Ru4(µ3-H)2{µ-Ph2As(CH2)nEPh2}(CO)12](M = Cu or Ag; E = As or P; n= 1 or 2). X-Ray crystal structure of [Cu2Ru4(µ3-H)2{µ-Ph2As(CH2)2PPh2}(CO)12]