Nanoarchitectonics of Glass Coatings for Near-Infrared Shielding: From Solid-State Cluster-Based Niobium Chlorides to the Shaping of Nanocomposite Films

The high potential of [{Nb6Cli12}La6] cluster-based building blocks as near-infrared radiation blockers for energy saving applications is exposed in the present paper (i = inner edge-bridging ligand, a = apical ligand of the Nb6; L = H2O and/or Cl). To do so, a combined experimental and theoretical investigation of edge-bridged [{Nb6Cli12}Cla6–x(H2O)x]m+/0/n− cluster unit series (x = 0, 4, 6; m = 2, 3, 4; n = 2, 3, 4) has been carried out. By using the K4[{Nb6Cli12}Cla6] starting solid-state precursor, we explored the behavior of the [{Nb6Cli12}Cla6]4– cluster unit during the different steps of its integration as a building block into a polyvinylpyrrolidone (PVP) matrix to form a glass coating composite denoted {Nb6Cli12}m+@PVP (m = 2 or 3). The optical, vibrational and redox properties [{Nb6Cli12}Cla6–x(H2O)x]m+/0/n− building blocks have been interpreted with the support of electronic structure calculations and simulation of properties. The chemical modifications and oxidation properties have been identified and studied thanks to various techniques in solution. Combining Raman and ultraviolet–visible spectroscopies, electrochemistry, and quantum chemical simulations, we bring new knowledge to the understanding of the evolution of the properties of the [{Nb6Cli12}Cla6–x(H2O)x]m+/0/n− cluster units as a function of the number of valence electron per cluster (VEC) and the nature of terminal ligands (x = 0, n = 4; x = 4, charge = 0; x = 6, m = 4). The fine understanding of the physical properties and vibrational fingerprints depending on the VEC and chemical modifications in solution are mandatory to master the processing of cluster-based building blocks for the controlled design and shaping of glass coating nanocomposites. On the basis of this acquired knowledge, [{Nb6Cli12}Cla6–x(H2O)x]m+/0/n− building blocks were embedded in a PVP matrix. The resulting {Nb6Cli12}2+@PVP nanocomposite film shows excellent ultraviolet (UV, 280–380 nm) and near-infrared (NIR, 780–1080 nm) blocking ability (>90%) and a highly visible light transmittance thanks to the controlled integration of the {Nb6Cli12}2+ cluster core. The figures of merit (FOM) value of Tvis/Tsol (Tvis = visible transmittance and Tsol = solar transmittance) as well as the haze, clarity, and the NIR shielding values (SNIR) were measured. After optimization of the integration process, a {Nb6Cli12}2+@PVP nanocomposite on glass substrate has been obtained with a high FOM equal to 1.29. This high value places the transparent green olive {Nb6Cli12}2+@PVP nanocomposites at the top system in the benchmark in the field of glass coating composites for energy-saving applications.