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

• A new Ni(II) complex with Br … Br halogen interactions was obtained. • Two types of Br … Br contacts influence the halogen bonding synthon formation. • The hydrogen and Br … Br contacts increase the stability of the Ni(II) complex. • The Br…Br contacts disturb the ε solvent, promoting spectral changes by solvatochromic effect. 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)(H 2 O) 3 ]•CH 3 OH was synthesized by the reaction between [Ni(tmeda)].(NO 3 ) 2 (tmeda = N , N , N’ , N’ -tetramethylethylenediamine) and K 2 TBrPh. 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-OH 2 … 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, CH 3 CN, chlorinated solvents), and solvent-dependent absorption maxima presents linear behavior as a function of their dielectric constant.