INTERSTITIALLY-STABILIZED PRASEODYMIUM(III) COMPOUNDS NA2PR4BR9NO ANDPR8BR13N3O - STRUCTURES ON THE BORDER BETWEEN SALTS AND CLUSTERS

The title compounds are obtained in high yields after appropriate reac tions in sealed Nb tubing at similar to 750-950 degrees C in nonreduce d systems but only when both O and N sources are included in the appro priate proportions. The structures of both have been established by si ngle crystal means. (Na2Pr4Br9NO: P2(1)/m, Z = 2, a = 8.543(4) Angstro m, b = 11.707(3) Angstrom, c = 9.697(4) Angstrom, beta = 106.49(3)degr ees, R, R(w) = 3.7, 4.9%. Pr8Br13N3O: C2/c, Z = 4, a = 21.967(8) Angst rom, b = 8.355(2) Angstrom, c = 16.889(7), beta = 119.40(3)degrees, R, R(w) = 2.9, 3.1%.) The former is isotypic (but not isoelectronic) wit h the known Na2Pr4Cl9O(2). Both phases contain infinite zigzag chains of N- and O-centered Pr-4 tetrahedra sharing trans edges, and both app ear to be Pr-III valence compounds. They can also be geometrically rel ated to reduced compounds like Pr4I5Ru with infinite octahedral chains and are thus on the borderline between reduced, metal-rich cluster ph ases and ''simple'' salts.