Two new heteroleptic pentacoordinated Zn(II) complexes (1 and 2) containing 4,4′-disubstituted 2,2′-bipyridines as the main ligand and curcumin (curc) as an ancillary ligand have been synthesized, spectroscopically and structurally characterized, and tested in vitro towards different human cancer cell lines. While the nitrogen ligands are almost inactive, Zn(II) curc derivatives 1 and 2 show promising and selective anticancer properties. In particular the curc Zn(II) complex 1 shows the strongest growth inhibition in all cell lines, being even more effective than the pure curc in the LAN-5 neuroblastoma cell line. Furthermore, the curc moiety makes the complexes 1 and 2 fluorescent, a feature enabling investigation of their interaction with DNA through a new optical method previously tested with the reference fluorescent intercalator ethidium bromide. This analysis demonstrates that the interaction mode of curc, 1 and 2 with DNA in the double helix favors their alignment perpendicular to the DNA axis, suggesting a partial inter-base intercalation of these Zn(II) complexes.

High-resolution X-ray diffraction experiments and state-of-the-art density functional theory calculations have been performed. The validity of the atoms-in-molecules approach is tested for the neutral–ionic transition of TTF-CA which involves a transfer of less than one electron between the donor and acceptor molecules. Foremost, crystallographical data have been reassessed along the temperature-induced neutral–ionic phase transition undergone by this charge transfer complex. Based on accurate X-ray structures at 105 and 15 K, topological analysis of both DFT and the experimental multipolar electron densities allowed detailed characterization of intra- and interstack intermolecular interactions. Direct quantification of the intermolecular charge transfer and the dipole moment are discussed.

The phase transition of 1:1 mixed-stack organic charge-transfer crystal of tetrathiafulvalene-$p$-bromanil (TTF-BA) has been investigated by high resolution x-ray diffraction. The temperature-induced phase transition to a nonmagnetic state at 53 K was characterized by a dimeric distortion of the donor-acceptor stack similar to that observed in charge transfer complexes displaying a neutral-to-ionic transition. But in this case the dimerization process does not change the charge transfer between donor and acceptor molecules. Molecular packing in mixed stacks along two orthogonal crystallographic axes and the role of inter- and intrastack interactions are discussed.