Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

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Electronic structure and spectroscopic properties of the ground and low-lying excited states of SnSi within 4 eV have been investigated by using a multireference singles and doubles configuration interaction (MRDCI) method that includes relativistic effective core potentials. Potential energy curves of a number of Lambda-S states of singlet, triplet, and quintet spin multiplicities are constructed. Spectroscopic parameters (T(e), r(e), omega(e), D(e), and mu(e)) of 27 bound Lambda-S states are reported. The ground state of SnSi belongs to the X(3)Sigma(-) symmetry with an estimated dissociation energy (D(e)) of 2.49 eV. However, with the inclusion of the spin-orbit coupling, D(e) reduces to 2.11 eV. Spectroscopic properties of at least 36 Omega states are determined. Transition probabilities of several singlet-singlet and triplet-triplet transitions are calculated. Partial radiative lifetimes of some of these transitions are estimated. A number of weak Omega-Omega transitions with partial radiative lifetimes of the order of milliseconds or more is also predicted here.