The optimized geometries, harmonic vibrational frequencies, and energies of the structures of monohydrated alloxan were computed at the DFT/ωB97X-D and B3LYP/6-311++G** level of theory. Results confirm that the monohydrate exists as a dipolar alloxan-water complex which represents a global minimum on the potential energy surface (PES). Trajectory dynamics simulations show that attempt to reorient this monohydrate, to a more favorable orientation for H-bonding, is opposed by an energy barrier of 25.07 kJ/mol. Alloxan seems to prefer acting as proton donor than proton acceptor. A marked stabilization due to the formation of N-H-OH2 bond is observed. The concerted proton donor-acceptor interaction of alloxan with one H2O molecule does not increase the stability of the alloxan-water complex. The proton affinity of the O and N atoms and the deprotonation enthalpy of the NH bond of alloxan are computed at the same level of theory. Results are compared with recent data on uracil, thymine, and cytosine. The intrinsic acidities and basicities of the four pyrimidines were discussed. Results of the present study reveal that alloxan is capable of forming stronger H-bonds and more stable cyclic complex with water; yet it is of much lower basicity than other pyrimidines.
<p>The X-ray spectroscopic signatures of solvated Co<sup>2+</sup> ions mimicking the aqueous solution of CoCl<sub>2</sub> are investigated accounting for multiconfigurational as well as spin-orbit coupling effects. To this end the RASSCF/RASSI methodology with second order corrections due to dynamical correlation (RASPT2) is employed. Emphasis is put on the identification of spectral signatures of different species in octahedral, [Co(H<sub>2</sub>O)<sub>6</sub><sub>-</sub><sub>x</sub>Cl<sub>x</sub>]<sup>(2</sup><sup>-</sup><sup>x)+</sup>, and tetrahedral, [Co(H<sub>2</sub>O)<sub>4</sub><sub>-</sub><sub>x</sub>Cl<sub>x</sub>]<sup>(2</sup><sup>-</sup><sup>x)+</sup>,coordination. X-ray absorption spectra show distinct differences in the L<sub>3</sub> band only. Here, the best agreement is obtained for the hexa-aqua complex [Co(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>. For better identification it is proposed to use RIXS spectroscopy, which shows pronounced species-dependent inelastic features.</p><p><br></p>
<p>The X-ray spectroscopic signatures of solvated Co<sup>2+</sup> ions mimicking the aqueous solution of CoCl<sub>2</sub> are investigated accounting for multiconfigurational as well as spin-orbit coupling effects. To this end the RASSCF/RASSI methodology with second order corrections due to dynamical correlation (RASPT2) is employed. Emphasis is put on the identification of spectral signatures of different species in octahedral, [Co(H<sub>2</sub>O)<sub>6</sub><sub>-</sub><sub>x</sub>Cl<sub>x</sub>]<sup>(2</sup><sup>-</sup><sup>x)+</sup>, and tetrahedral, [Co(H<sub>2</sub>O)<sub>4</sub><sub>-</sub><sub>x</sub>Cl<sub>x</sub>]<sup>(2</sup><sup>-</sup><sup>x)+</sup>,coordination. X-ray absorption spectra show distinct differences in the L<sub>3</sub> band only. Here, the best agreement is obtained for the hexa-aqua complex [Co(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>. For better identification it is proposed to use RIXS spectroscopy, which shows pronounced species-dependent inelastic features.</p><p><br></p>
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