Macrocyclic cyclodiphosphazane $$[\{\hbox {P}(\mu \hbox {-}^{t}\hbox {BuN})\}_{2}(\hbox {O}-m-\hbox {C}_{6}\hbox {H}_{4}\hbox {CHNCH}_{2})_{2}]_{2}$$ [ { P ( μ - t BuN ) } 2 ( O - m - C 6 H 4 CHNCH 2 ) 2 ] 2 : synthesis of chalcogen derivatives and gold(I) complex