Mapping the formation areas of giant molybdenum blue clusters: a spectroscopic study

Abstract

The self-assembly of soluble molybdenum blue species from simple molybdate solutions has primarily been associated with giant mixed-valent wheel-shaped cluster anions, derived from the {Mo^V/VI_154/176} archetypes, and a {Mo^V/VI₃₆₈} lemon-shaped cluster. The combined use of Raman spectroscopy and kinetic precipitation as self-assembly monitoring techniques and single-crystal X-ray diffraction is key to mapping the realm of molybdenum blue species by establishing spherical {Mo^V/VI₁₀₂}-type Keplerates as an important giant molybdenum blue-type species. We additionally rationalize the empirical effect of reducing agent concentration on the formation of all three relevant skeletal types: wheel, lemon and spheres. Whereas both wheels and the lemon-shaped {Mo^V/VI₃₆₈} cluster are obtained from weakly reduced molybdenum blue solutions, considerably higher reduced solutions lead to {Mo^V/VI₁₀₂}-type Keplerates.