Two trinuclear Cu^II pyrazolato complexes with a Cu₃(μ₃-E)-core (E = O^2– or OH^–) and terminal nitrite ligands in two coordination modes were characterized crystallographically, spectroscopically, and electrochemically. One-electron oxidation of the μ₃-O species produces a delocalized, mixed-valent, formally Cu^II₂Cu^III-nitrite, but no nitrate. In contrast, under reducing conditions—addition of PhSH as an electron and proton donor—both complexes mediate the reduction of nitrite, releasing NO.

A combination of detailed magnetisation studies and electronic-structure analysis using broken-symmetry DFT is used to explore the electronic structure of a trigonal prismatic Cu^II ₆ cluster. The presence of six paramagnetic metal centres with S = 1/2 gives rise to a maximum multiplicity of S = 3 and a total of 31 broken-symmetry states with M_S < 3. Computed differences in energy between the high-spin and broken-symmetry states are expressed in terms of the 15 distinct Heisenberg exchange coupling parameters, J_ij, and the equations are solved by a least-squares fitting procedure. By inspection of the errors introduced by progressive symmetrisation of the Hamiltonian to reduce the number of independent J_ij, we arrive at a minimal model containing only four distinct J_ij (three intra- and one inter-triangular). The computed values then guide the fitting of the magnetisation data. The computed trends in J_ij can only be reproduced when antisymmetric exchange is included in the model Hamiltonian. The use of this Hamiltonian provides a reasonable description of the magnetic behaviour at all temperatures and fields. If a simpler isotropic model Hamiltonian is used instead, the best fit values of J_ij are compromised by the need to fit the low-temperature region where antisymmetric exchange dominates the shape of the curve.

Five pyrazole-based tripodal ligands, compounds 1–5, based on a 1,3,5-triethylbenzene scaffold, show aggregation-induced emission enhancement (AIEE) and their application as fluorescent probes for detection of nitroaromatics is investigated. All five compounds are weakly fluorescent in THF, but their fluorescence intensity increases with the addition of a poor solvent (water), causing nanoaggregation, as confirmed by the changes in the UV-vis and emission spectra, and light scattering techniques. The nanoaggregates exhibit time-dependent emission characteristics and can serve as sensors for the detection of nitroaromatic compounds. The selective detection of picric acid (PA) over other nitroaromatic compounds by 1–3 is attributed to the photoinduced electron transfer from the trispyrazole to the quencher, as confirmed by TD-DFT calculations. Furthermore, compounds 1 and 2 were tested for sensing of PA in the vapor and solid phases by means of changes in the emission spectra observable by the naked eye. The supramolecular assemblies of 1 and 3 with PA were structurally characterized by X-ray crystallography.