Crystal Structure, Spectroscopic Studies and Supramolecular Chemistry, DFT Based Electronic and Optical Properties of Salts of Methylene Blue with Tetrahedral Anions

Abstract The Fe(III), Ni(II) and Zn(II) salts were treated with MB + to obtain metal complexes MB[FeCl 4 ], (MB) 2 [NiCl 4 ], MB(ClO 4 ) and to explore the coordination behavior of the organic cation. Crystals were grown by soft grinding and solution techniques. The resultant compounds were fully characterized by UV‐visible spectroscopy, TGA, single crystal and powder XRD. UV‐Visible, Frontier molecular orbital, Density of states, Molecular electrostatic potentials, and band gap were estimated theoretically by DFT. The purity and crystallinity of material was measured with the help of powder X‐ray diffraction analysis while their thermal stability was measured with the help of thermogravimetric analysis. DFT study revealed that the chlorinated metal center helps to stabilize the HOMO and LUMO values which are ultimately responsible for the lower energy gap. Complex (MB) 2 [NiCl 4 ] has the lowest bandgap 0.48 eV which is due to the presence of one extra MB + and also due to the electron‐rich nature of Ni(II). The crystal structure of all compounds is stabilized by strong electrostatic, hydrogen bonding, π‐π‐stacking and other short‐interactions. Molecular electrostatic potentials ESP surface shows that chlorinated metal centers are electron rich in nature and more electron density are found in center. The supramolecular chemistry of the resultant solids is discussed in detail.