Terminal Gold-Oxo Complexes

In contradiction to current bonding paradigms, two terminal Au-oxo molecular complexes have
been synthesized by reaction of AuCl3 with metal oxide-cluster ligands that model redox-active metal oxide
surfaces. Use of K10[α2-P2W17O61]·20H2O and K2WO4 (forming the [A-PW9O34]9- ligand in situ) produces
K15H2[Au(O)(OH2)P2W18O68]·25H2O (1); use of K10[P2W20O70(OH2)2]·22H2O (3) produces K7H2[Au(O)(OH2)P2W20O70(OH2)2]·27H2O (2). Complex 1 crystallizes in orthorhombic Fddd, with a = 28.594(4) Å, b =
31.866(4) Å, c = 38.241(5) Å, V = 34844(7) Å3, Z = 16 (final R = 0.0540), and complex 2 crystallizes in
hexagonal P6(3)/mmc, with a = 16.1730(9) Å, b = 16.1730(9) Å, c = 19.7659(15) Å, V = 4477.4(5) Å3, Z
= 2 (final R = 0.0634). The polyanion unit in 1 is disorder-free. Very short (∼1.76 Å) Au-oxo distances are
established by both X-ray and 30 K neutron diffraction studies, and the latter confirms oxo and trans aqua
(H2O) ligands on Au. Seven findings clarify that Au and not W is present in the Au-oxo position in 1 and 2.
Five lines of evidence are consistent with the presence of d8 Au(III) centers that are stabilized by the flanking
polytungstate ligands in both 1 and 2:  redox titrations, electrochemical measurements, 17 K optical spectra,
Au L2 edge X-ray absorption spectroscopy, and Au-oxo bond distances. Variable-temperature magnetic
susceptibility data for crystalline 1 and 2 establish that both solids are diamagnetic, and 31P and 17O NMR
spectroscopy confirm that both remain diamagnetic in solution. Both complexes have been further
characterized by FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and
other techniques.