Crystal structure and anti/syn-conformational isomers of trans-bis[dibromobis(2,2-dimethyl-1,3-propanediamine)chromium(III)] tetrabromozincate

Abstract

A new complex, trans-anti/syn-[CrBr2(Me2tn)2]2ZnBr4 (1) (Me2tn = 2,2-dimethyl-1,3-propanediamine, C5H14N2), was prepared, and its structure was characterized by single-crystal X-ray diffraction and infrared (IR) spectroscopy. The complex crystallizes in the orthorhombic space group, Pnma, with eight formula units in a cell with dimensions of a = 16.415(3), b = 41.130(8), and c = 12.372(3) Å. X-ray structural analysis reveals three crystallographically independent Cr(III) complex cations in the complex. In the complex cations, Cr(III) ions are coordinated by four N atoms belonging to the two chelating Me2tn and two bromides, in a trans arrangement, displaying a distorted octahedral geometry. Interestingly, the asymmetric unit contains one-half of a centrosymmetric trans-anti-[Cr1Br2(Me2tn)2]+ (2) cation, one independent trans-syn-[Cr2Br2(Me2tn)2]+ (3) cation, another half of a trans-syn-[Cr3Br2(Me2tn)2]+ (4) cation, and one ZnBr42− anion. The [Cr1Br2(Me2tn)2]+ (2) cation adopts anti chair–chair conformation, whereas the [Cr2Br2(Me2tn)2]+ (3) and [Cr3Br2(Me2tn)2]+ (4) cations adopt syn chair–chair conformations. The Cr–N(Me2tn) bond lengths vary from 2.077(4) to 2.102(5) Å, and the Cr–Br bond lengths range from 2.4177(14) to 2.4933(10) Å. ZnBr42− anion possesses a slightly distorted tetrahedral geometry in which the Zn–Br bond lengths and Br–Zn–Br angles are influenced by hydrogen-bonding interactions. The crystal lattice is stabilized by the hydrogen-bonding interactions between the bromides and NH groups of the Me2tn ligands.