Structure of Bis(Lidocaine) Tetrachloridoferrate(III) Chloride

The present chapter reports on the synthesis and structure of bis(2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide) or bis(lidocaine) tetrachloridoferrate(III) chloride. The complex with the formula (C₁₄H₂₃ON₂)₂[FeCl₄].Cl (or (LidH)₂[FeCl₄].Cl), crystallizes in the monoclinic space group P2₁/c with a = 11.0597(1), b = 23.0083(2), c = 14.6629(2) Å, β = 109.378(2)deg;, V = 3519.82(8) Å3, Z = 4, and D_c = 1.328 Mg/m³. The coordination of the Fe³⁺ ion with four chlorine anions generates slightly distorted tetrahedral anion [FeCl₄)]^-, while two protonated cations LidH⁺, as well as one chlorine anion Cl- remain in an outer coordination sphere. The formation of a network of hydrogen bonds involves amine and amide nitrogen atoms, as well as carbonyl oxygen atoms of lidocaine cations: the amide nitrogen atom of one cation and the protonated nitrogen atom of the amino group of another cation form relatively weak hydrogen bonds with the “isolated” chlorine atom, while the nitrogen atoms of the amino groups also participate in the formation of strong intramolecular N-H…O hydrogen bonds. The anion 292is associated with cations only by weak “non-classical” hydrogen bonds of the C-H…Cl type, but the relatively strong intermolecular N-H…O hydrogen bonds form a “bridge” connecting two protonated lidocaine molecules of neighboring (LidH)₂[FeCl₄ ].Cl complexes with the formation of molecular dimers. “Bridges” are located in the center and in all eight corners of the unit cell, half of the ligands of the complex form dimers, the other half stacks with the metal group and chlorine anions. The dimers form a chain lying in the ac plane and on the diagonal passing through the origin at an angle of 54.69® (0.5β) to the a and c axes; the chains form layers lying in the ac plane with an interlayer distance of 11.5 Å (0.5b), and layers containing anions and cations not involved in the formation of dimers are arranged between the dimer layers.