The title compound CH3ReO3 (1), the simplest organometallic oxide known to date, undergoes an aggregation process in aqueous solution which is unprecedented in organometallic chemistry. From the acidic colorless solutions of 1 in water, a golden-colored, highly refractory precipitate separates slowly at room temperature or within hours at 70 degrees C. The product 2 forms in 70% yield, with the composition of vacuum-dried material being {H-0.5[(CH3)(0.92)ReO3]}(infinity). Thus, only 8% of the original methyl groups eliminate during formation of 2 in water. The nonstoichiometric compound ("poly-MTO") represents the first known "polymeric" organometallic oxide. The most striking physical properties-golden color, graphite-like consistence, reflectance, electric conductivity, weak paramagnetism-result from a two-dimensional structure containing a sufficient concentration of d(1) Re-VI centers to establish the electric conductivity of the material. The Re-VI centers mostly originate from homolytic loss of methyl groups (Re-VII --> Re-VI) during formation of "poly-MTO" (2). Thermal degradation in moist atmosphere yields highly pure, crystalline rhenium trioxide, which itself is an electrically conducting material.