Exploring supramolecular C-Br…Br-C interactions as organizing tools in a novel Ni(II)-tetrabromophthalate complex. Crystal structure and solvatochromism studies

The understanding of the non-covalent halogen^…halogen interaction inside coordination complexes has special interest as design tools in crystal engineering and coordination chemistry. In this work, we show the use of the supramolecular C-Br^…Br-C interactions as a tool in the crystalline organization of a Ni(II) complex and its solvatochromic properties. To do so, we selected the 3,4,5,6-tetrabromophthalate (TBrPh) ligand where the Br atoms pointing outside to favor their self-assembly through these interactions.

Thus, a novel complex, [Ni(tmeda)(TBrPh)(H₂O)₃]•CH₃OH was synthesized by the reaction between [Ni(tmeda)].(NO₃)₂ (tmeda = N, N, N’, N’-tetramethylethylenediamine) and K₂TBrPh. The Ni(II)-complex was structurally analyzed by single-crystal X-ray diffraction, Hirshfeld surfaces, multiple analytical tools and DFT calculations.

Structural analysis shows that Ni(II)-complex has 1D supramolecular chains based on the cooperativity of intra/inter-molecular charged-assisted hydrogen bonds of type Ni-OH₂^…O and C_sp2-Br^…Br-C_sp2 interactions into 2D networks. These Br^…Br interactions organize the crystal packing in the solid state as is evidenced by the molecular electrostatic potential studies and Plot of Hirsfeld surface.

This Ni(II)-complex displays solvatochromism with a wide range of solvents (alcohols, DMF, CH₃CN, chlorinated solvents), and solvent-dependent absorption maxima presents linear behavior as a function of their dielectric constant.