(Nitro-[kappa]N)[2-(phenyldiazenyl-[kappa]N²)pyridine-[kappa]N](2,2':6',2''-terpyridine-[kappa]³N)ruthenium(II) tetrafluoroborate

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), Ru-N_nitro 2.066 (3) Å, and Ru-N_tpy 2.082 (4), 1.982 (3) and 2.074 (4) Å. The azo N atom is trans to the nitro group. The azo N=N bond length is 1.265 (5) Å, 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.