The development of efficient B12N12-based toxic gas sensors has received considerable attention from the scientific community. Thus, in this regard, quantum chemical calculations were performed using density functional theory (DFT) at the B97D/6-31G­(d,p) level for all of the studied systems. Modification of copper on B12N12 results in five optimized structures, named CuB11N12 and B12N11Cu (doped structures), Cu@b66 and Cu@b64 (decorated structures), and Cu@B12N12 (encapsulated structure). The results indicate that the CO gas weakly physisorbed on the B12N12 nanocage. It was found that the gas adsorption performance of B12N12 is improved due to the introduction of the Cu atom, but the interaction between CO and B12N11Cu, Cu@B12N12, Cu@b64, and Cu@b66 nanocages is strong, limiting the applications as a sensor. Particularly, the CuB11N12 system shows moderate adsorption (E ads = −0.6 eV) and a high electronic sensitivity (ΔE gap = 81.6%) toward CO gas, compared to other modified systems. Furthermore, based on the sensor performance analysis, it was found that CuB11N12 presented low recovery time (14 ms) and high selectivity for CO detection, making it a promising fast response sensor. Finally, our results demonstrated the capability of CuB11N12 as a superior sensor material for applications involving the selective detection of CO gas.

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Theoretical chemistry calculations using the Density Functional Theory (DFT) were carried out to understand the interaction between oxygen (O2) and MnN4 type manganese-based complexes during the formation of MnN4-O2 adducts. In order to understand how this interaction is affected by different macrocyclic ligands, O2 was bonded to manganese-porphyrin (MnP), manganese-octamethylporphyrin (MnOMP), manganese-tetraaza[14]annulene (MnTAA), manganese-dibenzo [b,i] [1, 4, 8, 11]-tetraaza [14] annulene (MnDBTAA), manganese-2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(tim)Mn](2+)), and manganese-2,3,9,10-tetraphenyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(ph-tim)Mn](2+)). The binding and activation of the oxygen molecule was facilitated by an increasing trend in the O-O bond lengths and a decreasing one in the O-O vibrational frequency, with preference for the O2 side-on interaction among MnN4 macrocycles. The catalytic activities of the MnN4 complexes toward the O2 binding process increased in the following order: [(ph-tim)Mn](2+) < MnP < MnOMP < MnDBTAA < MnTAA < [(tim)Mn](2+). Therefore, it was concluded that the [(tim)Mn](2+)complex was the most active for the binding and activation of molecular oxygen.

Density functional theory (DFT) was used to examine the interaction between molecular oxygen (O₂) and macrocyclic iron complexes of the type FeN₄ during the formation of FeN₄--O₂ adducts. In order to understand how this interaction is affected by different macrocyclic ligands, O₂ was bonded to iron-tetraaza[14]annulene (FeTAA), iron-tetramethyl-tetraaza[14]annulene (FeTMTAA), iron-hexamethyl-tetraaza[14]annulene (FeHMTAA), iron dibenzotetraaza[14]annulene (FeDBTAA), and two iron-tetramethyl-dibenzotetraaza[14]annulene complexes (FeTMDBTAA1, FeTMDBTAA2). The ground state for FeN₄-O₂ adducts was the open-shell singlet. Analysis of the factors influencing the O₂ bonding process showed that different macrocyclic ligands yielded adducts with differences in O--O and Fe--O₂ bond lengths, total charge over the O₂ fragment, O--O vibrational frequency, and spin density in the O₂ fragment. A smaller energy gap between the α-HOMO of the FeN₄ complexes and the β-LUMO of O₂ increased the interaction between the complex and the O₂ molecule. The order of activity was FeDBTAA < FeTMDBTAA2 < FeTMDBTAA1 < FeTAA < FeTMTAA < FeHMTAA.

This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH, and CN) on the aromaticity of borazine (BNH), using density functional theory (DFT) and the Hartree-Fock (HF) method. The calculations to optimize the geometries, structural properties, and vibrational frequencies were performed using the same 6-311G(d,p) and 6-311++G(d,p) basis sets, comparing the methods with experimental results. In the analysis of the NICS values, it was found that that replacing the hydrogen atoms by halogen atoms (F, Cl, and Br) and CH reduced the aromaticity of the borazine molecule, while use of the CN group resulted in NICS values (0.9-2.0 Å) very close to those of borazine, presenting the following order of increasing aromaticity: BNH-(Br) < BNH-(Cl) < BNH-(F) < BNH-(CH) < BNH ~ BNH-(CN). All the spectra of the compounds showed only the presence of transition peaks distant from the UV region, reflecting the large energy difference between the HOMO and LUMO orbitals. After the substitution of the borazine ring, all the compounds presented an intensification of the spectrum, with a shift of the maximum absorbance toward red, indicative of a bathochromic effect. There was a direct inverse relation between the energy gap and the maximum wavelength of the compounds.

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