The Ru-N bond distances in the title complex, [Ru(NO2)(C11H9N3)(C15H11N3)]BF4 or [Ru(NO2)(tpy)(azpy)]BF4, [tpy is 2,2' :6',2 " -terpyridine and azpy is 2-(phenylazo)pyridine], are Ru-N-py 2.063 (4), Ru-N-azo 2.036 (4), R-D N-nitro 2.066 (3) Angstrom, and Ru-N-tpy 2.082 (4), 1.982 (3) and 2.074 (4) Angstrom. The azo N atom is trans to the nitro group. The azo N N bond length is 1.265 (5) Angstrom, which is the shortest found in such complexes to date. This indicates a multiple bond between Ru and the N atom of the nitro group, and pi -backbonding [d pi (Ru) --> pi*(azo)] is decreased.