SYNTHESES AND ELECTROCHEMISTRY OF [MO(NO)(HB(MPPZ)3)-CL(ER)] (MPPZ = 3-P-METHOXYPHENYLPYRAZOL-1-YL E=O OR NH R=PH OR C6H4ME-2) AND THE CRYSTAL-STRUCTURES OF [MO(NO)(HB(MPPZ)3)CL(OPH)] AND [MO(NO)(HB(MPPZ)3)CL(NHC6H4ME-2)]

The new complexes [Mo(NO){HB(mppz)3}Cl(ER)] (mppz = 3-p-methoxyphenylpyrazol-1-yl; E = O or NH; R = Ph or C6H4Me-2) have been prepared and the structures when E = O, R = Ph and E = NH, R = C6H4Me-2 determined by X-ray crystallographic methods. The reduction potentials of the new complexes are similar to those of their counterparts containing the tris(3,5-dimethylpyrazolyl)hydroborate ligand. A comparison of the structures of 24 molybdenum mononitrosyl complexes containing tris(pyrazolyl)borate ligands variously substituted in the 3 position indicates that variations in the steric demands of the ligand set are primarily accommodated by changes in the angles made at the molybdenum atom by the coligands rather than those made by the tris(pyrazolyl)borate ligand.