ca. °C under dinitrogen (heating rate 10 °C/min) and at more elevated temperatures yield the ceramic products 3a-d. Ceramic yields by TGA were in the range of 18% (for 2b) to 66% (for 2d) at 600 °C and in the range of 17% (2b) to 45% (2c, 2d) at 1000 °C. Pyrolysis of a 1:1 blend of the polymers 2c and 2d afforded the ceramic 3e in 62% yield at 600 °C and the highest ceramic yield by TGA at 1000 °C (56%). Controlled pyrolysis experiments in a tube furnace under N2 permitted the isolation of the black, lustrous ceramics 3a-e together with several molecular depolymerization products. The ceramics 3a (formed at 600 and 1000 °C) and 3b and 3e (formed at 600 °C) were characterized by scanning electron microscopy (SEM) with energy-dispersive X-ray microanalysis (EDX) and back-scattered electron imaging (BEI). These techniques indicated that these materials were iron silicon carbides. The ceramic 3a formed at 600 °C was found to be amorphous, whereas the corresponding ceramic formed at 1000 °C was shown to contain a-Fe crystallites by powder X-ray diffraction (XRD). Mossbauer and magnetization measurements carried out on the ceramics 3a, 3b, and 3e indicated that the materials were soft ferromagnets. Identification of several volatile molecular byproducts produced during pyrolysis provided evidence for the operation of unusual decomposition/depolymerization pathways. The unsymmetrical dimer Fel^-CsIL^-(,«-SiMe2)2(?7-C5H3)Fe(?7-C5H5) (4a) was formed during the pyrolysis of 2a, and this species was characterized by single-crystal X-ray diffraction. Cyclic voltammetry studies of 4a in CH2CI2 showed that this species undergoes two reversible and sequential one-electron oxidations (separation AE1/2 = 0.26 V) consistent with redox coupling between the iron centers. Triphenylsilylferrocene, FeOz-CsHsK^-CoEDSiPhs), was isolated as one of the volatile pyrolysis products derived from 2b. Crystals of 4a are monoclinic, space group P2\/n, with a = 9.3842( 2) A, b = 15.455(2) A, c = 15.6630(12) A; 0 = 91.092(6)°; Z = 4; V = 2271.2(11) A3 456.possess useful physical properties such as tensile strength and high thermal stability.4-9 Transition-metal-containing solid-state materials are also desirable ceramic University of Toronto.

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). An X-ray difrraction study of 4 a indicated significant strain. Polymer 5 a was crystalline and insoluble in common organic solvents and was characterized by solid-state 13C NMR. Polymer 5b, which was soluble in organic solvents, was characterized by ' H and I3C NMR, UV/visible spectroscopy and elemental analysis. Its molecular weight distribution was bimodal (gel permeation chroinatography: M," = 9.6 x Nandyala P. Raju, John E. Greedan, Stephen Barlow and lo4, M , = 8.6 x lo4 for the high molecular weight fraction, M , = 4.8 x lo3, M , = 3.5 x lo3 for the oligomeric fraction), suggesting two polymerization mechanisms. The UV/visible spectrum implied a localized structure for the polymer backbone. Cyclic voltammetry revealed that 5 b undergoes two reversible oxidations in CH,Cl, solution at -0.25 and -0.16 V. The redox coupling is indicative of only a sinall degree of interaction between the iron centres. Ther-

When heated at 500°C under nitrogen the poly(ferrocenylsi1anes) [ F~(Y-C~H~)~(S~R~) ]~