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Mononuclear ruthenium complex 1and dinuclear complex 2were synthesized by reaction of the appropriate bidentate pyrazolyl-pyridyl-based ligand L (L = 1,4-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene) with cis-Ru(bipy)2Cl2·2H2O. They were characterized by elemental analyses, ESI-MS, 1H spectroscopy, and X-ray crystallography for 2. Compounds 1and 2both emit strongly in solid states and in solutions at 298 K with the lifetimes in the microsecond range. Electrogenerated chemiluminescence (ECL) of complexes 1and 2in the absence or presence of coreactant tri-n-propylamine (TPrA) or 2-(dibutylamino)ethanol (DBAE) at different working electrodes in acetonitrile and phosphate buffer solutions (PBS, pH 7.5) was studied. The ECL spectra are identical to the photoluminescence spectra, indicating that the ECL emissions are due to the metal to ligand charge transfer (MLCT). In all cases, ECL quantum efficiencies of dinuclear complex 2are higher than those of mononuclear complex 1, and ECL quantum efficiencies of complexes 1and 2/TPrA system are higher than those of DBAE system. It is noted that diuretic furosemide tends to decrease the ECL intensity of complex 2/TPrA system in PBS (pH 7.5) at GC working electrode. A novel ECL method for the determination of diuretic furosemide was developed with a linear range between 2.0 × 10−7mol L−1and 1.0 × 10−6mol L−1, and a detection limit of 1.2 × 10−8mol L−1based on 3 times the ratio of signal-to-noise. [ABSTRACT FROM AUTHOR]