Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline

Abstract

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

Charge density studies of single and transient (single to double) boron–oxygen bonds in (NH4)2B4O5(OH)4·2H2O

“…Anyway, experimental and theoretical results seem to be inconsistent in this case. In the second example, the paper written by Jarzembska et al , 27 there are four boron–oxygen bonds. Two of the bond lengths were longer than 1.46 Å, with the value of charge density being ca .…”

“…However, in this case the topological analysis of the theoretical charge density distributions was performed with TOPOND14 In table 5 In the literature, charge density has already been described in the case of several structures containing boron. [26][27][28][29] Although some of them include B O, those manuscripts were not directly focused the bond charge and types. However, information about the properties at BCP's of such bonds (see Table 6) is presented in some of them.…”

“…data XD theor. data Table 6 Parameters of properties at (3,−1) BCPs taken from the literature 26,27 Experimental Theoretical Dalton Transactions Paper Fig. 3 presents the comparison of properties at BCPs such as the electron density and its Laplacian obtained from both experimental and theoretical data.…”

Heteroelement Analogues of Benzoxaborole and Related Ring Expanded Systems

“…Importantly, the electroluminescence properties of complexes 8 and 14 was proved by testing OLEDs containing those compounds as emitters [10]. Later on, complex 8 became the subject of in-depth structural characterization, which included interesting solvatomorphic behaviour [11] as well as high resolution single-crystal X-ray diffraction electron density studies performed for the first time in the case of a luminescent oxyquinolinato organoboron complex [12]. Furthermore, 2 was also employed for the synthesis of a series of luminescent (O,N)-chelate complexes (15)(16)(17)(18) with 2-(imidazo [1,2-a]pyridin-2-yl)phenol ligands (Scheme 7) [13].…”