FIR spectra were recorded on the same instrument in transmission mode using CsI-pellets. UV–vis spectra were measured on a Perkin-Elmer Lambda 20 UV–vis spectrophotometer using samples dissolved in DMSO, DMF (dimethylformamide), THF (tetrahydrofuran), water or methanol. Electrospray ionization mass spectrometry was carried out with a Bruker Esquire 3000 instrument (Bruker Daltonics, Bremen, Germany) by using methanol and water as solvents. Expected and measured isotope distributions were compared. The X-band EPR spectra were recorded on a modified Varian E-4 spectrometer (Chicago, Roosevelt University).

Cyclic voltammograms were measured in a three-electrode cell using a 2 mm diameter glassy carbon Etoposide in vivo disk working electrode, a platinum auxiliary electrode and an Ag∣Ag+ reference electrode containing 0.1 M AgNO3. Measurements were performed at room temperature using an EG&G PARC potentiostat/galvanostat model 273A. Deareation of solutions was accomplished by passing a stream of argon through the solution for 5 min prior to the measurement and then maintaining a blanket atmosphere of argon over the solution during the measurement. The potentials were measured in 0.2 M (n-Bu4N)[BF4]/DMSO using [Fe(η5-C5H5)2] check details (E1/2ox = + 0.68 V vs NHE (normal hydrogen electrode)) [44] as internal standard and are quoted relative to NHE. The 1H, 13C and 15N

NMR spectra were recorded at 500.32, 125.82 and 50.70 MHz on a Bruker DPX500 (Ultrashield Magnet) in DMSO-d6. 2D 13C,1H HSQC,15N,1H HSQC (heteronuclear single quantum coherence), 13C,1H HMBC (heteronuclear multi-bond correlation spectroscopy) and 1H,1H COSY (correlation almost spectroscopy) experiments were also performed. X-ray diffraction measurement was

carried out on a Bruker X8 APEXII CCD diffractometer. Single crystal of 1·H2O was positioned at 40 mm from the detector, and 972 frames were measured, each for 20 s over 1° scan width. The data was processed using SAINT software [45]. Crystal data, data collection parameters, and structure refinement details are given in Table 1. The structure was solved by direct methods and refined by full-matrix least-squares techniques. Os, Cl and O atoms were refined with anisotropic displacement parameters, while C and N atoms isotropically. H atoms were inserted in calculated positions and refined with a riding model. The coordinated 2H-indazole was found to be disordered over two positions related by a plane of symmetry through Os1, three chloride ligands, atoms N1 and C1. The indazolium cation was found to be disordered over four symmetry related (pairwise) positions. The following software programs and computer were used: structure solution, SHELXS-97; refinement, SHELXL-97 [46]; molecular diagrams, ORTEP-3 [47]; computer, Intel CoreDuo. CH1 (ovarian carcinoma, human) cells were donated by Lloyd R. Kelland (CRC Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, U.K.).