Pr3Se2SiN3: The first nitrido-cyclo-trisilicate with discrete [Si3N9]15- anions according to Pr9Se6[Si3N9]

The oxidation of praseodymium metal with selenium and sodium azide, and additives of praseodyminum trichloride and sodium chloride as flux, in evacuated silica tubes at 900 C for 7 days, assisted by the reaction with the container material (SiO2) yielded dark yellow rods of an anionically derivatized nitrido-cyclo-trisilicate of trivalent praseodymium with the composition Pr3Se2SiN3, better Pr9Se6[Si3N9] (a = 1892.41(9), c = 1037.25(6) pm; trigonal, R anti 3, Z = 6), as a by-product, while actually attempting to synthesize praseodymium nitride selenides. The crystal structure contains three crystallographically different Pr3+ cations. Two of them are sevenfold coordinated each and the third one eightfold by two different Se2- and three independent N3- anions, respectively. However, discrete nitrido-cyclo-trisilicate units [Si3N9]15- appear as the main characteristic in the foreground, whose six-ring structure is realized via three corner-sharing [SiN4]8- tetrahedra (d(Si-N) = 172-179 pm; and angsph;(N-Si-N) = 101-116 ; and angsph;(Si-N-Si) = 117 ). (Abstract Copyright [2004], Wiley Periodicals, Inc.)