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Crystal Structure Design and Luminescence Performance of NIR Phosphors
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
where h characterizes anion ligands and k is central cations. When anions or ionic complexes are put in the order of increasing h-parameter, the well-known nephelauxetic effect series is obtained, i.e., no ligands < F− < H2O < NH3 < Cl− < Br− < N3− < I2− < O2− < S2− < Se2− and H2O < SO42− < CO32− < PO43− < BO33− < SiO44− < AlO45− < O2−. The reduction of interelectron repulsion and the increase of h-parameter are often ascribed to the sharing of electrons between central cation and surrounding ligands. Therefore, the movement of centroid shift is also related to covalency between activator ions and surrounding anion ligands. The larger centroid shift will happen in the higher covalency (detailed discussion is exhibited in Section 2.2.1). On the one hand, coordination numbers of ligand anion can affect covalency owing to interaction between central cations and ligands. Schematic diagram is presented in Figure 2.12(a).
Heteroleptic Co(III) bisdithiocarbamato-dithione complexes: Synthesis, structure and bonding of [Co(Et2dtc)2(R2pipdt)]BF4 (R = Me, 1; Ph, 2; pipdt = piperazin-2,3-dithione) complexes
Published in Journal of Coordination Chemistry, 2022
Flavia Artizzu, Luciano Marchiò, Luca Pilia, Angela Serpe, Paola Deplano
The chemical reactivity descriptors retrieved from DFT-calculated energy values of the HOMO and LUMO orbitals for the homoleptic dithiocarbamate complex [Co(Et2dtc)3] and the substituted [Co(Et2dtc)2(Ph2pipdt)]+ derivative are reported in Table 3. The global softness σ, which represents the tendency of the electron cloud to be distorted under external perturbation, is significantly higher in [Co(Et2dtc)2(Ph2pipdt)]+ than in the homoleptic dithiocarbamate complex, thus confirming the previous observation that the dithioxamide ligand induces a reduction of nephelauxetic effect and therefore a more extended charge delocalization. The remarkable difference in the electrophilicity index ω values further confirms this conclusion, underlining the increased capability of the cationic heteroleptic [Co(Et2dtc)2(Ph2pipdt)]+ complex to accommodate an extra charge with respect to the dithiocarbamate homoleptic precursor.
Dy(III) complexes of metformin Schiff-bases as glucose probe: synthesis, spectral, and thermal properties
Published in Journal of Coordination Chemistry, 2019
Marwa A. Mahmoud, Enas T. Abdel-Salam, Nadia F. Abdel Aal, Zeinab M. Showery, Shehab A. Sallam
The β and δ values are comparable with those for complexes of oxygen-nitrogen donor Schiff-base ligands [41–45]. The spectra show a shift of the band to lower energy compared with those of the water coordinated complex owing to nephelauxetic effect [46]. These parameters measure the amount of 4f-ligand mixing, i.e. covalence. The values of these parameters for the complexes are given in Table 2 which show that the metal–ligand bonding is covalent as compared to lanthanide ions with water, or that the 4f electrons are more localized [37].
Experimental and theoretical studies on structure, bonding and luminescence properties of Eu(III) and Tb(III) complexes of a new macrocyclic based 8HQ ligand
Published in Journal of Coordination Chemistry, 2019
The electronic structure and the nature of chemical bond in coordination compounds are explained on basis of ligand field theory (LFT) which has combined the idea of crystal field theory (CFT) and MO theory (MOT) within the introduction of the covalent character in the electrostatic nature of the metal-ligand bond. The first principle quantum chemical method ab initio (AI) and density functional theory (DFT) have been applied for elucidation of the electronic behavior and bonding in transition and inner transition metal complexes which in conjugation with LFT to calculate the nephelauxetic effect and ligand field parameters, result in AILFT (ab initio LFT) and LF-DFT (ligand field density field theory) [53]. The ADF program was used for ligand field DFT calculations. The hybrid BLYP-D3 functional 260 was used to calculate the electronic structure and the corresponding optical properties. For the Eu and Tb atoms, the MOs were extended by triple-zeta polarization (TZP) Slater-type orbital (STO) functions. Only weak spectral bands were detected experimentally for f–f transitions in the current case due to the dominance of ligand band. On a theoretical point of view, these are due to the electron interaction and spin-orbit interaction. The Slater Condon parameters and spin-orbit coupling constants (in cm−1) are calculated for europium and terbium complexes. The theoretical spin-orbit coupling constants are ζ4f 0.073 for europium and ζ4f 0.0965 for terbium. It may be noted that the Slater’s integral parameters F0 (ff), F2 (ff), F4 (ff) and F6 (ff) act mainly on the single-open shell 4fn configurations. The nephelauxetic effect is quantitatively defined though β is a nephelauxetic parameter, equal to the ratio between the interaction repulsion parameters (either Ek Racah’s parameter or Fk Slater’s integral) in the complex and in the free ion.