The electronic, magnetic, and optical properties of kekulene dimers bridged by Group 11 metals (Cu, Ag, Au) via a 2O–M–2O linkage are investigated using density functional theory. Despite their common Group 11 identity, the systems exhibit markedly different behaviors. 2Kek–Cu and 2Kek–Au adopt high-spin quartet ground states (S = 3/2) with quasi-linear extended C–O–TM–O–C arrangements and bent O–TM–O bridges, whereas 2Kek–Ag stabilizes a doublet (S = 1/2) with severe distortion (O–Ag–O = 125.9°). Natural bond orbital analysis reveals strong donor–acceptor stabilization for Cu (16.34 kcal/mol) and Au (16.24 kcal/mol), contrasted with weak interaction for Ag (5.04 kcal/mol). Optical spectra show visible excitations (489–601 nm), with Ag exhibiting the lowest transition coefficient. Extending to trimeric 3Kek–Au yields a septet (S = 3) with ferromagnetic coupling (J = +5.21 meV) between Au centers. This work establishes structure–property relationships wherein geometric integrity and effective d–p hybridization are essential for stabilizing high-spin magnetic ground states.
Double perovskite hydrides have recently gained significant consideration for solid state hydrogen storage because of their chemically flexible, structural stability, and tunable metal‑hydrogen interactions. Herein, first-principles density functional theory (DFT) calculations were conducted in CASTEP package to explore the structural, dynamical, electronic, mechanical, optical, thermodynamic, and hydrogen-storage properties of cubic LiMTi2H6 (M = Na, K, Rb, and Cs) double perovskite hydrides. The thermodynamic, dynamical, and mechanical stability were confirmed through negative formation energies (−4.16 to −2.95), absence of imaginary phonon modes, and Born stability criteria. All compounds exhibit metallic nature as confirmed by PBE-GGA approximation and HSE06 hybrid functions, coupled with strong absorption of ~3.5 × 105 cm−1, high refractive indices, and conductivity. Furthermore, the gravimetric hydrogen-storage capacity decreases from 4.27 wt% for LiNaTi2H6 to 2.45 wt% for LiCsTi2H6, whereas the desorption temperature decreases from 482.6 K to 384.7 K, reveals that hydrogen release effectively controlled by alkali-metal substitution (Na, K, Rb, and Cs). The calculated mechanical moduli's further indicate stiffness, ductile, and elastic anisotropy behavior. These results demonstrate that alkali-metal substitution provides an effective approach for hydrogen-storage characteristics of LiMTi2H6 (M = Na, K, Rb, and Cs) double perovskite hydrides.
Inspired by recent advances in metalloborosperhenes, we performed a comprehensive density functional theory (DFT) investigation into the electrocatalytic activity of La3B18 and Tb3B18 nanoclusters toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among the studied metalloborosperhenes, Tb3B18 is predicted to exhibit the most thermodynamically favorable Gibbs free energy for hydrogen adsorption (ΔGH* = −0.12 eV), suggesting its superior suitability for HER compared to the alternative La3B18 substrate within the employed computational model. The Volmer-Heyrovsky mechanism is generally more favorable under conditions of high hydrogen coverage, where HH recombination proceeds efficiently, compared to the Volmer-Tafel pathway. In addition, Tb3B18 is predicted to exhibit enhanced OER activity, characterized by a lower calculated thermodynamic overpotential (ηOER = 0.59 V) relative to its La3B18 counterpart. We found that the superior predicted OER activity of Tb3B18 relative to La3B18 can be rationalized by two critical factors including favorable ground-state electronic properties, namely the lower atomic charge on Tb atoms, and advantageous excited-state electronic properties, specifically the localization of the LUMO on the transition-metal active sites. These findings identify Tb3B18 metalloborosperhene as a promising theoretical candidate for bifunctional catalysis, motivating future experimental validation.
