Tetrahedrally coordinated aluminate Al(OH)₄^- and dialuminate Al₂O(OH)₆^2- anions are considered to be major species in aluminum-rich alkaline solutions. However, their relative abundance remains difficult to spectroscopically quantify due to local structure similarities and poorly understood effects arising from extent of polymerization and counter-cations. To help unravel these relationships here we report detailed characterization of three solid-phase analogues as structurally and compositionally well-defined reference materials. We successfully synthesized a cesium salt of the aluminate monomer, CsAl(OH)₄·2H₂O, for comparison to potassium and rubidium salts of the aluminate dimer, K₂Al₂O(OH)₆, and Rb₂Al₂O(OH)₆, respectively. Single crystal and powder X-ray diffraction methods clearly reveal the structure and purity of these materials for which a combination of ²⁷Al MAS-NMR, Al K-edge X-ray absorption and Raman/IR spectroscopies was then used to fingerprint the two major tetrahedrally coordinated Al species. The resulting insights into the effect of Al-O-Al bridge formation between aluminate tetrahedra on spectroscopic features may also be generalized to the many materials that are based on this motif.

Boehmite (γ-AlOOH) and gibbsite (α-Al-(OH)₃) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications. Developing the ability to understand and predict the properties and characteristics of these materials, on the basis of their natural growth or synthesis pathways, is an important fundamental science enterprise with wide-ranging impacts. The present study describes bulk and surface characteristics of these novel materials in comprehensive detail, using a collectively sophisticated set of experimental capabilities, including a range of conventional laboratory solids analyses and national user facility analyses such as synchrotron X-ray absorption and scattering spectroscopies as well as small-angle neutron scattering. Their thermal stability is investigated using in situ temperature-dependent Raman spectroscopy. These pure and effectively defect-free materials are ideal for synthesis of advanced alumina products.