Metallocyclo- and polyphosphazenes containing gold or silver: thermolytic transformation into nanostructured materials.
A cyclotriphosphazene bearing two 4-oxypyridine groups on the same phosphorus atom, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4)(2)] (I), and its analogous polymer [{NP(O(2)C(12)H(8))}(0.7){NP(OC(5)H(4)N-4)(2)}(0.3)](n) (II), have been used to prepare gold or silver, cyclic and polymeric, metallophosphazenes. The following complexes, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{ML})(2)] (ML=Au(C(6)F(5)) (1) or Au(C(6)F(5))(3) (2)), [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AuPPh(3)})(2)][NO(3)](2) (3), and [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AgPPh(2)R})(2)][SO(3)CF(3)](2) (R=Ph (4) or Me (5)) have been obtained. Complexes 1 and 4 are excellent models for the preparation of the analogous polymers [{NP(O(2)C(12)H(8))}(0.7){NP(OC(5)H(4)N-4{ML})(2)}(0.3)](n) (ML=Au(C(6)F(5)) (P1), Ag(OSO(2)CF(3))PPh(3) (P2)). All complexes have been characterized by elemental analysis, various spectroscopic methods, and mass spectrometry. The polymers were further investigated by thermochemical methods (thermogravimetric analysis) and differential scanning calorimetry. For compounds 1-5 and for the starting phosphazene I, a mixture of different stereoisomers may be expected. The stereochemistry in solution has been studied by variable-temperature NMR spectroscopy studies, which provided evidence for interconversion processes that involve changes in the chirality of a 2,2'-dioxybiphenyl group. A single-crystal X-ray analysis of the gold complex 2 confirmed not only the proposed structure, but also S,S and R,R configurations at the two biphenoxy-substituted phosphorus centers, in contrast to those observed for the precursor I. Pyrolysis of these new metallophosphazenes was also studied. Notably, pyrolysis of the gold derivatives gave macroporous metallic gold sponges without the requirement of either an external reducing agent or a porous support. These materials were all characterized by XRD, TEM, SEM, and energy-dispersive X-ray spectroscopy.
Jiménez
Josefina
J
Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., Facultad de Ciencias, 50009 Zaragoza, Spain. jjimvil@unizar.es
Laguna
Antonio
A
Benouazzane
Mohamed
M
Sanz
Jose Antonio
JA
Díaz
Carlos
C
Valenzuela
María Luisa
ML
Jones
Peter G
PG