Metallocyclo‐ and Polyphosphazenes Containing Gold or Silver: Thermolytic Transformation into Nanostructured Materials

Abstract

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.

Nanostructured copper oxides and phosphates from a new solid-state route

“…This corroborates our previous results that pyrolysis of organometallic derivatives of cyclotriphosphazenes yields metallic nanostructured phosphates or pyrophosphates [19][20][21][22][23][24][25][26]. The results from precursor II also corroborate this hypothesis even if no cyclophosphazenes are present since the phosphine acts as the source of phosphorus atoms.…”

“…These precursors are depicted in Scheme 1 and will be denoted throughout the paper as precursors (I) -(VII). As we previously reported, the use of metallic derivatives of phosphazenes as precursors leads to the formation of phosphorus-containing nanoparticles of phosphates or pyrophosphates [19][20][21][22][23][24][25][26]. With the aim of designing an alternative method to obtain nanostructured materials of metal oxides without using phosphorus, we show that this is possible using precursors I, II, VI and VII (see Scheme 1).…”

“…As previously mentioned, the pyrolysis of the precursors I-VII were performed at 800 °C in air [19][20][21][22][23]. Pyrolysis of precursors I and II result in CuO, as evidenced by their powder XRD patterns.…”

“…In this way, the diffraction from the grid is avoided and the observed area is minimized. The pyrolysis experiments were carried out, as previously reported [19][20][21][22][23][24][25][26], by pouring a weighed portion (0.05-0.15 g) of the solid on aluminum oxide boats placed in a furnace (Lindberg/Blue Oven model STF55346C-1) under a flow of air, heated from 25 to 300 °C and then to 800 °C, and annealed for 2 h. Raman spectra (using a 50 × objective)…”

Layered Graphitic Carbon Host Formation during Liquid-free Solid State Growth of Metal Pyrophosphates

“…By comparison, relatively few solid-state strategies for pure metallic nanostructured materials have been reported [18][19][20][21][22] . In recent work [23][24][25][26][27][28][29] , we reported a new solid-state method allowing the formation of metallic (M), oxidic (M x O y ) and (pyro)phosphate-based (M x P y O z ) nanostructured materials without necessitating liquids or solutions. Detailed investigations have shown that the resulting structures and their shapes strongly depend on the metal used, which can be a noble, transition or valve metal, and also on the molecular precursors to which the metal centers are coordinated.…”