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

Abstract

The high potential of [{Nb 6 Cl i 12 }L a 6 ] 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 Nb 6 ; L = H 2 O and/or Cl). To do so, a combined experimental and theoretical investigation of edge-bridged [{Nb 6 Cl i 12 }Cl a 6−x (H 2 O) 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 K 4 [{Nb 6 Cl i 12 }Cl a 6 ] starting solid-state precursor, we explored the behavior of the [{Nb 6 Cl i 12 }Cl a 6 ] 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 {Nb 6 Cl i 12 } m+ @PVP (m = 2 or 3). The optical, vibrational and redox properties [{Nb 6 Cl i 12 }Cl a 6−x (H 2 O) 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 [{Nb 6 Cl i 12 }Cl a 6−x (H 2 O) 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, [{Nb 6 Cl i 12 }Cl a 6−x (H 2 O) x ] m+/0/n− building blocks were embedded in a PVP matrix. The resulting {Nb 6 Cl i 12 } 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 {Nb 6 Cl i 12 } 2+ cluster core. The figures of merit (FOM) value of T vis /T sol (T vis = visible transmittance and T sol = solar transmittance) as well as the haze, clarity, and the NIR shielding values (S NIR ) were measured. After optimization of the integration process, a {Nb 6 Cl i 12 } 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 {Nb 6 Cl i 12 } 2+ @PVP nanocomposites at the top system in the benchmark in the field of glass coating composites for energy-saving applications.

Controlling the Deposition Process of Nanoarchitectonic Nanocomposites Based on {Nb6−xTaxXi12}n+ Octahedral Cluster-Based Building Blocks (Xi = Cl, Br; 0 ≤ x ≤ 6, n = 2, 3, 4) for UV-NIR Blockers Coating Applications

“…For these two specific values, surprisingly the most intense signal corresponds to the composition unit x + 1. In the same way, the results of mass spectrometry studies for the dispersion in acetone, in negative mode, also showed similarities with the homometallic clusters compounds, i.e., an oxidation of the cluster units without apical ligand substitution as expected (Table S2) [7,21,22,30] 2+ (with n = 5, 6; m = 0,1 and n + m = 6) cluster units could be detected. The important point is that the cluster units are not oxidized in alcohol media as for water-based solutions.…”

“…The dissolution of K 4 [{Nb 6-x Ta x X i 12 }X a 6 ] cluster compounds (X = Cl, Br; 1 ≤ x ≤ 5) in water leads to a solution of the stable species [{Nb 6-x Ta x X i 12 }(H 2 O) a 6 ] 2+ (X = Cl, Br; 1 ≤ x ≤ 5). It should be noted that for x = 1, we detected the presence of [{Nb 5 Ta 1 X i 12 }(H 2 O) a 5 (OH) a 1 ] + (X = Cl, Br) motifs in aqueous solution and this is analogous to that of the x = 0 homometallic [21,22,30]. For x > 1, no unit containing a hydroxyl apical ligand was detected.…”

“…As expected, the UV-Vis-NIR spectra of the heterometallic clusters have intermed shapes to those observed for the homometallic clusters and fully confirm the possib As expected, the UV-Vis-NIR spectra of the heterometallic clusters have intermediate shapes to those observed for the homometallic clusters and fully confirm the possibility to tune the optical properties of the nanocomposites. For the ESI-MS studies, the dispersion in water showed similarities with homometallic clusters compounds (x = 0 and 6), with a total substitution of the 6 apical ligands by H 2 O molecules and no signal in negative mode [7,21,22,30]. The dissolution of K 4 [{Nb 6-x Ta x X i 12 }X a 6 ] cluster compounds (X = Cl, Br; 1 ≤ x ≤ 5) in water leads to a solution of the stable species [{Nb 6-x Ta x X i 12 }(H 2 O) a 6 ] 2+ (X = Cl, Br; 1 ≤ x ≤ 5).…”

“…It is well known that the pH modifies the hydrolysis and condensation reaction rates and at the end, modifies the structure of the polymers formed. Moreover, previous studies on Nb 6 or Ta 6 metal atom clusters indicated a strong correlation between the pH value and the VEC values of the clusters [7,30]. Several solutions containing the water-ethanol mixture have been prepared and the pH was adjusted between 2 and 7 by adding acid (hydrochloric acid, nitric acid, acetic acid or oxalic acid).…”

“…12 }-Y@PVP Films PVP is the second example of matrixes used in these works, and it is often a good candidate complementary to the SiO 2 -PEG matrix. Indeed, the PVP is a nontoxic, biodegradable and biocompatible polymer with an interesting temperature resistance and pH stability, recently used for energy and optical applications [11,12,14,30,32,33,[39][40][41][42][43][44][45][46][47]. These results, especially thus on thin films, have shown that it is clearly possible to incorporate inorganic nanoparticles or nanoclusters directly at high concentrations into a PVP matrix without observing any segregation between the organic and inorganic phases.…”