A new metastable binary compound with the skutterudite crystal structure has been synthesized from modulated elemental reactants, through an amorphous intermediate, using a novel low-temperature synthesis technique. The amorphous reaction intermediate undergoes nucleation at 87 degreesC, an extremely low temperature for solid-state reactions. When heated above 350 degreesC, the metastable phase NiSb3 disproportionates into the thermodynamically stable phases NiSb2 and Sb. Also, if the sum of the individual elemental layer thicknesses is greater than 30 Angstrom, a mixture of different phases forms. Simulation of the high-angle powder X-ray diffraction spectrum confirms that NiSb3 is isostructural with CoSb3.