(E)-(4-Methoxyphenyl)-N-(4H-1,2,4-triazol-4-yl) methanimine: Solvent driven single molecule triple fluorescent “on” sensor for Cu2+, Cd2+ and Hg2+

213-217A single molecule, (E)-(4-methoxyphenyl)-N-(4H-1,2,4-triazol-4-yl) methanimine (Metho-tria-imine), can detect Cu2+, Cd2+ or Hg2+ depending on whether the solvent is H2O, CH3CN or C2H5OH respectively by fluorescence “on” mode. The enhancement in fluorescence intensity is found to be ca. 13 times for Cu2+, 70 times for Cd2+ and 57 times for Hg2+. The metal ions - Al3+, Co2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Zn2+ (along with two metal ions out of Cu2+, Cd2+ and Hg2+ for which the sensor is not effective) do not interfere. The plot of absorbance versus metal ion concentration was sigmoidal for Cu2+ and Cd2+ and linear for Hg2+ which indicates formation of dimeric complexes in solution for Cu2+ and Cd2+. DFT studies showed metal-metal bonding in case of Metho-tria-imine forming complexes with Cu2+ and Cd2+ and hence dimeric complexes with highest binding energy for Cu2+ in H2O, Cd2+ in CH3CN, Hg2+ in C2H5OH. The detection limits are found to be 1.9×10-8 M, 7.0×10-7 M and 6.9×10-8 M respectively and Metho-tria-imine is reversible with respect to EDTA2- for all the three metal ion

Theoretical Study on the Effect of Annelation and Carbonylation on the Electronic and Ligand Properties of <i>N</i>‑Heterocyclic Silylenes and Germylenes: Carbene Comparisons begin To Break Down

Quantum chemical calculations have been carried out to investigate the effect of annelation and carbonylation on the electronic and ligand properties of <i>N</i>-heterocyclic silylenes and germylenes. The thermodynamic stability of these ligands has been found to increase with annelation, while the reverse is true for carbonylation. This is in sharp contrast to N-heterocyclic carbenes (NHCs) where annelation leads to a decrease in their thermodynamic stabilities. Compared to nonannelated derivatives, annelated and carbonylated ones are found to be weaker σ donors but better π acceptors. The effect of carbonylation is more pronounced than annelation toward increasing the π acidity of these ligands. Carbonylation at the α-position with respect to the N atom attached to the Si/Ge center has been found to be the most effective way of enhancing the π acidity of these ligands. The computed natural charges reveal that electrophilicity increases upon both annelation and carbonylation. The calculated values of ³¹P NMR chemical shifts of corresponding phosphinidene adducts of these ligands have been found to correlate well with the π acidity of these Si/Ge centers

Ligand Properties of Boron-Substituted Five‑, Six‑, and Seven-Membered Heterocyclic Carbenes: A Theoretical Study

The electronic properties of boron-substituted five-, six-, and seven-membered heterocyclic carbenes have been studied using quantum chemical methods. The stability of carbenes has been examined from the values of their respective singlet–triplet and HOMO–LUMO gaps. Both the singlet–triplet and the HOMO–LUMO gaps indicate higher stability for six- and seven-membered P-heterocyclic carbenes (PHCs) containing boron atoms at the α position with respect to phosphorus atoms. While PHCs are better π acceptors, the π acidities of NHCs can be tuned by substituting a boron atom in the α position with respect to nitrogen. This is revealed by the energies of a π-symmetric unoccupied orbital centered at the central carbon atom. Reactivity of these carbenes has been discussed in terms of nucleophilicity and electrophilicity index. The calculated relative redox potential values and ¹³C NMR parameters are found to correlate well with the π acidities of the respective carbenes

Spectroscopic Distinction of Different Carbon Bases: An Insight from Theory

Spectroscopic differentiation based on the ¹³C NMR chemical shift of the parent and protonated derivatives of carbon­(II) and carbon(0) bases has been proposed. The ¹³C chemical shift of the central carbon atom of carbenes in their parent and protonated forms will experience more downfield shift, whereas the central carbon atom of carbones will experience a lesser downfield shift; such shifts for compounds that possess “hidden” carbon(0) characteristics will lie between these two extremes. The ¹³C chemical shifts of the protonated derivatives are solely dependent on the out-of-plane p_π occupancies of the central carbon atom. This difference arises due to their unique difference in bonding and may provide an easier distinction between these two classes of compounds

Nature of Intramolecular Metal–Metal Interactions in Supported Group 4–Group 9 and Group 6–Group 9 Heterobimetallic Complexes: A Combined Density Functional Theory and Topological Study

Quantum chemical calculations have been carried out on a series of supported group 4–group 9 and group 6–group 9 heterobimetallic complexes designated by the general formulas [Cp₂M­(μ-E)₂M′(H)­(CO)­L] and [(CO)₄M­(μ-E)₂M′(H)­(CO)­L] where E = SH, SeH or PH₂ and L = PH₃, CO, NHC, or <i>a</i>NHC. An analysis of the optimized geometries of these molecules indicates the presence of an M···M′ interaction. The nature of this interaction is investigated by using Bader’s quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and source function (SF). The results of QTAIM analysis suggest a polar covalent interaction between the two disparate metal centers in these heterobimetallic complexes. ELF analysis identifies a bonding basin between the two metal centers, while SF analysis reveals that the metal–metal bonding is moderately delocalized. The strength of the M···M′ interaction is found to be stronger in group 4–group 9 heterobimetallic complexes compared to group 6–group 9 ones

Electronic and Ligand Properties of Annelated Normal and Abnormal (Mesoionic) <i>N</i>‑Heterocyclic Carbenes: A Theoretical Study

The effect of annelation and carbonylation on the electronic and ligating properties of N-heterocyclic carbenes (NHCs) has been studied quantum chemically. The thermodynamic and kinetic stability of these NHCs have been assessed on the basis of their singlet–triplet and HOMO–LUMO gaps respectively. Both annelation and carbonylation have been found to decrease the stability of NHCs. Compared to nonannelated carbenes, annelated and carbonylated carbenes are found to be weaker σ donors but better π acceptors. However, the effect of carbonylation is more pronounced than annelation toward increasing the π acidity of the NHCs. The reactivity of these carbenes has been discussed in terms of nucleophilicity and electrophilicity indices. The calculated values of the relative redox potential and ³¹P NMR chemical shifts of corresponding carbene-phosphinidene adducts have been found to correlate well with the π acidity of the NHCs