Unexpected Nitrogen-Oxygen Exchange Reactions in Cyclic Metallaphosphazenes; Synthesis and X-Ray Crystal Structures of Cyclic (Mo(OPPh2NHPPh2O)O2Cl2), Cyclic (Mo(OPPh2NPPh2O)2(O)Cl), and Cyclic (Mo(OPPh2NPPh2O)2O2).