Boronate Ligands in Materials: Determining Their Local Environment by Using a Combination of IR/Solid‐State NMR Spectroscopies and DFT Calculations

Abstract

Boronic acids (R-B(OH)(2)) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R-B(OH)(3)(-)) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C(4)H(9)-B(OH)(3)](2), which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid-state NMR spectroscopy ((1)H, (13)C, (11)B and (43)Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave--GIPAW--method). These data allow relationships between the geometry around the OH groups in boronates and the IR and (1)H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic-inorganic materials containing boronate building blocks.

Coordination Networks Based on Boronate and Benzoxaborolate Ligands

“…Although these structures have an overall layered organization, as shown by powder X-ray diffraction analyses, the benzoxaborolates here play two different roles: either they bridge different metal cations, or they simply serve as counter-anions, as illustrated in Figure 7 for the Mgbenzoxaborolate decahydrate phase. [22][23][24]. For the octylboronate ligand, the same binding mode as for the butylboronate was observed [24].…”

“…For the octylboronate ligand, the same binding mode as for the butylboronate was observed [24]. Adapted with permission from [22] (copyright American Chemical Society, 2011), [23,24] (copyright Wiley-VCH Verlag 2013 and 2015) and [25] (copyright Actualité Chimique, 2014).…”

“…[22] (copyright American Chemical Society, 2011), [24] (copyright Wiley-VCH Verlag 2013) and [25] (copyright Actualité Chimique, 2014). Materials were isolated in most cases as microcrystalline powders [22][23][24]. Scanning electron microscopy (SEM) analyses showed that in many cases, the crystallites had a sheet-like morphology, as illustrated in Figure 4 for the Sr-phenylboronate monohydrate and Sr-butylboronate phases.…”

“…A series of investigations aiming at describing the intrinsic coordination properties of the R-B(OH)3 − anions in materials have been reported [22][23][24]. Boronic acids bearing non-coordinating R-chains were used for this purpose (R-= C6H5-, C4H9-, C8H17-), in order to ensure that the materials would form only based on the metal-ligand interactions.…”

“…Indeed, these ions should not lead to the competitive formation of metal-hydroxide precipitates during the reaction, in contrast with most other metal ions [20]. Materials were isolated in most cases as microcrystalline powders [22][23][24]. Scanning electron microscopy (SEM) analyses showed that in many cases, the crystallites had a sheet-like morphology, as illustrated in Figure 4 for the Sr-phenylboronate monohydrate and Sr-butylboronate phases.…”