Theoretical Modeling (Sparkle RM1 and PM7) and Crystal Structures of the Luminescent Dinuclear Sm(III) and Eu(III) Complexes of 6,6,7,7,8,8,8- Heptafluoro-2,2-dimethyl-3,5-octanedione and 2,3-Bis(2-pyridyl)pyrazine: Determination of Individual Spectroscopic Parameters for Two Unique Eu³⁺ Sites

Heteroleptic homo dinuclear complexes [Sm­(fod)3(μ-bpp)­Sm­(fod)3] and [Eu­(fod)3(μ-bpp)­Eu­(fod)3] and their diamagnetic analogue [Lu­(fod)3(μ-bpp)­Lu­(fod)3] (fod is the anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and bpp is 2,3-bis­(2-pyridyl)­pyrazine) are synthesized and thoroughly characterized. The lanthanum gave a 1:1 adduct of La­(fod)3 and bpp with the molecular formula of [La­(fod)3bpp]. The 1H NMR and 1H-1H COSY spectra of the complexes were used to assign the proton resonances. In the case of paramagnetic Sm3+ and Eu3+ complexes, the methine (of the fod moiety) and the bpp resonances are shifted in the opposite direction and the paramagnetic shifts are dipolar in nature, which decrease with increasing distance of the proton from the metal ion. The single-crystal X-ray analyses reveal that the complexes (Sm3+ and Eu3+) are dinuclear and crystallize in the triclinic P1 space group. Each metal in a given complex is eight coordinate by coordinating with six oxygen atoms of three fod moieties and two nitrogen atoms of the bpp. Of the two metal centers, in a given complex, one has a distorted square antiprism arrangement and the other acquires a distorted dodecahedron geometry. The Sparkle RM1 and PM7 optimized structures of the complexes are also presented and compared with the crystal structure. Theoretically observed bond distances are in excellent agreement with the experimental values, and the RMS deviations for the optimized structures are 2.878, 2.217, 2.564, and 2.675 Å. The photophysical properties of Sm3+ and Eu3+ complexes are investigated in different solvents, solid, and PMMA-doped thin hybrid films. The spectroscopic parameters (the Judd–Ofelt intensity parameters, radiative parameters, and intrinsic quantum yield) of each Eu3+ sites are calculated using the overlap polyhedra method. The theoretically obtained parameters are close to the experimental results. The lifetime of the excited state is 38.74 μs for Sm3+ and 713.62 μs for the Eu3+ complex in the solid state