DFT calculations in the assignment of solid-state NMR and crystal structure elucidation of a lanthanum(III) complex with dithiocarbamate and phenanthroline

The molecular, crystal, and electronic structures as well as spectroscopic properties of a mononuclear heteroleptic lanthanum(III) complex with diethyldithiocarbamate and 1,10-phenanthroline ligands (3 : 1) were studied by solid-state C-13 and N-15 cross-polarisation (CP) magic-angle-spinning (MAS) NMR, X-ray diffraction (XRD), and first principles density functional theory (DFT) calculations. A substantially different powder XRD pattern and C-13 and N-15 CP-MAS NMR spectra indicated that the title compound is not isostructural to the previously reported analogous rare earth complexes with the space group P2(1)/n. Both C-13 and N-15 CP-MAS NMR revealed the presence of six structurally different dithiocarbamate groups in the asymmetric unit cell, implying a non-centrosymmetric packing arrangement of molecules. This was supported by single-crystal X-ray crystallography showing that the title compound crystallised in the triclinic space group P1. In addition, the crystal structure also revealed that one of the dithiocarbamate ligands has a conformational disorder. NMR chemical shift calculations employing the periodic gauge including projector augmented wave (GIPAW) approach supported the assignment of the experimental C-13 and N-15 NMR spectra. However, the best correspondences were obtained with the structure where the atomic positions in the X-ray unit cell were optimised at the DFT level. The roles of the scalar and spin-orbit relativistic effects on NMR shielding were investigated using the zeroth-order regular approximation (ZORA) method with the outcome that already the scalar relativistic level qualitatively reproduces the experimental chemical shifts. The electronic properties of the complex were evaluated based on the results of the natural bond orbital (NBO) and topology of the electron density analyses. Overall, we apply a multidisciplinary approach acquiring comprehensive information about the solid-state structure and the metal-ligand bonding of the heteroleptic lanthanum complex.