Unusual Reduction of Ammonium Heptamolybdate to Novel
Molybdenum(IV)-Stabilized Azo Anion Radical Complexes
Anasuya Sanyal
Priyabrata Banerjee
Gene-Hsiang Lee
Shie-Ming Peng
Chen-Hsiung Hung
Sreebrata Goswami
10.1021/ic049671e.s002
https://acs.figshare.com/articles/dataset/Unusual_Reduction_of_Ammonium_Heptamolybdate_to_Novel_Molybdenum_IV_Stabilized_Azo_Anion_Radical_Complexes/3315916
In an unusual reaction of the polyacid, ammoniumheptamolybdate tetrahydrate ((NH<sub>4</sub>)<sub>6</sub>[Mo<sub>7</sub>O<sub>24</sub>]·4H<sub>2</sub>O), and the
ligand, 2-[(arylamino)phenylazo]pyridine (general abbreviation HL), in the presence of PPh<sub>3</sub> afforded the brown oxo
free molybdenum complexes of type [Mo(L)<sub>2</sub>] in high yields (ca. 80%). The reaction occurs smoothly in ethanol. It
is slow on a steam bath (25 h) but is complete in about an hour in a microwave oven. X-ray structures of two
representatives are reported. In these complexes the ligand acted as a tridentate ligand using its pyridyl(N), azo(N),
and the deprotonated amine(N), respectively. The geometry is meridional, and the relative orientations within the
coordinated pairs of nitrogens are <i>cis</i>, <i>trans</i>, and <i>cis,</i> respectively. Bond length data of the coordinated ligands are
consistent with a Mo<sup>IV</sup>[L<sup>•</sup>]<sub>2</sub> ([L<sup>•</sup>]<sup>2-</sup> = azo dianion radical formed by one electron reduction of the deprotonated
anionic ligand, [L]<sup>-</sup>) description. For example, the N−N lengths (1.349(5)−1.357(2) Å) in these complexes are
appreciably longer than that (1.246(3) Å) in the uncoordinated and protonated salt of a representative ligand,
[H<sub>2</sub>L<sup>d</sup>]ClO<sub>4</sub>. The N−N lengths, however, correspond well with metal complexes of the ligand containing azo ion
radical. The complexes are diamagnetic and showed highly resolved <sup>1</sup>H NMR and <sup>13</sup>C NMR spectra. The two
coordinated ligands in these are magnetically equivalent, and resonances for only one ligand were observed in
their spectra. Diamagnetism in the present molybdenum complexes is attributed to strong antiferromagnetic coupling
between Mo<sup>IV</sup>(4d<sup>2</sup>) and the two planar radical [L<sup>•</sup>]<sup>2-</sup> ligands. The complexes display multiple redox responses. The
ESR spectrum of electrogenerated [<b>1a</b>]<sup>-</sup> showed a characteristic spectrum for Mo(III) with weak hyperfine lines
due to the presence of molybdenum isotopes having nonzero nuclear spin. Visible range multiple charge transfer
transitions in these complexes are ascribed to ligand-to-metal transitions.
2004-11-15 00:00:00
1 H NMR
ligand
charge transfer transitions
13 C NMR spectra
molybdenum complexes
HL
ESR
Mo
H 2 L
bond length data
NH
IV