Homodinuclear lanthanoid(III) dithiocarbamato complexes bridged by 2,2′-bipyrimidine: Syntheses, structures and spectroscopic properties

Abstract

Four new homodinuclear lanthanoid(III) dithiocarbamato (RR'dtc -) complexes bridged by 2,2'bipyrimidine (bpm) of the form [{Ln(RR'dtc)3}2(µ-bpm)] {Ln = Nd or Eu; RR' = dimethyl-(Me2) or pyrrolidine-(pyr)} were prepared and their crystal structures and spectroscopic properties were characterized. Crystallographic studies revealed that all of the complexes possess a similar structural motif with an 8:8-coordination geometry, in which bpm bridges two Ln III centers in the κ 2 N 1,1' :κ 2 N 3,3' mode and three RR'dtcligands coordinate to each Ln III center.The complexes exhibited weak but relatively sharp f-f transition bands in the absorption and magnetic circular dichroism (MCD) spectra recorded in the visible region. The MCD spectral studies demonstrated the magneto-optical behavior of the complexes. The spectral features of the dithiocarbamato complexes were distinctly different from those of the β-diketonato analogues, suggesting the coordination environment around the Ln III center influences the electronic structure and spectroscopic symmetry of the complexes in solution.

Noncovalent Interactions at Lanthanide Complexes

“…In most cases, the ′′young′′ noncovalent interactions, such as halogen, chalcogen, pnictogen, tetrel and rare‐earth bonds, have not been discussed in original publications, but we have evidenced (mainly on the basis of X‐ray structural data) their occurrence and role in stabilising ionic associates and clusters or forming reactive species in supramolecular chemistry of lanthanides, what deserves to be explored in future. Moreover, both bond parameters (strength and directionality) can be regulated by the attachment of substituents, [114] choice of Ln centre, [134,135,137] replacement of noncovalent bond acceptor site, [162] etc.…”

“…In most cases, the ''young'' noncovalent interactions, such as halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, have not been discussed in original publications, but we have evidenced (mainly on the basis of X-ray structural data) their occurrence and role in stabilising ionic associates and clusters or forming reactive species in supramolecular chemistry of lanthanides, what deserves to be explored in future. Moreover, both bond parameters (strength and directionality) can be regulated by the attachment of substituents, [114] choice of Ln centre, [134,135,137] replacement of noncovalent bond acceptor site, [162] etc. Supramolecular chemistry of lanthanides is not limited to the participation of coordinated ligand molecules in intermolecular interactions (via the secondary coordination sphere); thus, the Ln atom itself can also be involved in noncovalent bonds as a noncovalent donor leading to a rare-earth bond (in the primary coordination sphere), [80,81,163,164,166] which represents a new important area to design and application of lanthanide complexes for future development.…”

“…For instance, both tecton-solvent and solvent-solvent interactions, namely of halogen bonding type, were observed in lanthanide complexes (42)(43)(44) in chloroform solution (Scheme 10). [137] The Cl⋯S and Cl⋯Cl distances of 3.30 and 3.18 Å, respectively, are shorter than the sum of the van der Waals radii of the corresponding interacting atoms (Cl + S = 1.75 + 1.80 = 3.55 Å, [61] and Cl + Cl = 1.75 + 1.75 = 3.50 Å [61] ) (Scheme 10). The ffCÀ Cl⋯S and ffCÀ Cl⋯Cl angles are in the range of 167.34 to 168.96°, which also agrees with the halogen bonding term (Scheme 10).…”

“…The corresponding magnetic circular dichroism signals are dominated by room temperature C-terms and a characteristic negative B-term in 42 and 43, respectively. [137]…”

“…Tecton-solvent (a) and solvent-solvent (b) halogen bonding interactions. [137] Moreover, both mono-and di-chalcogen bond donor abilities of the sulphur atom of coordinated thiazole (thz) ligands are observed in the dinuclear praseodymium complex [Pr 2 Cl 6 (pyrazine)(thz) 6 ] (53) (Scheme 12b). [154] The intermolecular S ) the chalcogen bonds in aggregates of 53 appear to concern a σ-hole interaction, as illustrated in Scheme 12b.…”