Molybdenum(I) mononitrosyl complexes: syntheses, electrochemistry, electron paramagnetic resonance spectra and magnetism of complexes with N6 and N5I first-co-ordination spheres and the crystal structures of [Mo-{HB(dmpz)3}(NO)(NC5H4Ph-4)2]I and [Mo{HB(dmpz)3}(NO)-(NC9H7)2]BPh4(dmpz = 3,5-dimethylpyrazol-1-yl)

Abstract

The 17-electron, formally d⁵ molybdenum(I), complexes [Mo{HB(dmpz)₃}(NO)I(L)]({HB(dmpz)₃}= hydrotris-3,5-dimethylpyrazol-1-ylborate; L = pyridine, 4-phenylpyridine, phenanthridine or isoquinoline) and [Mo{HB(dmpz)₃}(NO)(L)₂]Z (L = 4-phenylpyridine, Z = I; L = isoquinoline, Z = I₃ or BPh₄) have been prepared and exhibit varied magnetic behaviour. The magnetic moments of [Mo{HB(dmpz)₃}(NO)I(L)](L = pyridine or isoquinoline) and [Mo{HB(dmpz)₃}(NO)(NC₉H₇)₂]BPh₄ are close to the spin-only value for one unpaired electron and do not vary significantly with temperature. The remaining complexes exhibit magnetic moments which increase from near the spin-only value at 6 K to substantially higher values at 300 K. The cationic complexes are reduced to 18-electron species at potentials which are almost invariant and ca. 400 mV more anodic than those of their neutral monoiodo counterparts, the reduction potentials of which vary over a range of ca. 150 mV in accord with the change in pK_a values of the heterocyclic ligands. The molecular structure of [Mo{HB(dmpz)₃}(NO)(NC₅H₄Ph-4)₂]I reveals dihedral angles of 41.0 and 29.9° between the aryl rings of the NC₅H₄Ph-4 ligands whilst the structure of [Mo{HB(dmpz)₃}(NO)(NC₉H₇)₂]BPh₄ reveals that, in the solid state at least, the two isoquinoline ligands do not form a ‘cleft’ which might act as a site for weak binding of an aryl group from the BPh₄^– ion.