Abstract
To identify the effects of halogen bonding in the architecture of Schiff base complex supramolecular networks, we introduced halogenated Schiff-base 3-Br-5-Cl-salen as ligand and isolated a new salen-type manganese(III) complex [MnIII(Cl)(H2O)(3-Br-5-Cl-salen)] (1) where 3-Br-5-Cl-salen = N,N’-bis(3-bromo-5-chlorosalicylidene)-1,2-diamine. The complex was investigated in the solid-state for halogen bonds (XBs) by single crystal X-ray structure analysis. Meanwhile, theoretical calculations were carried out to rationalize the formation mechanism of different types of XBs in the complex. The analysis result of electronic structure of the halogen bonds indicated that the chlorine atom coordinated to the Mn(III) center possesses the most negative potential and acts as anionic XB acceptor (electron donor) to the adjacent substituted halogens on the ligand, meanwhile the intermolecular Mn-Cl···X-C halogen bonding plays a significant role in directing the packing arrangement of adjacent molecules and linking the 2D layers into a 3D network. In order to verify the above results and acquire detailed information, the title complex was further analyzed by using the Hirshfeld surface analyses.
Highlights
Engineering well-defined molecules into specific crystal network has been one of the frontiers in material science [1,2,3]
The MEP for the title compound is scaled from −200 kJ mol−1 to +220 kJ mol−1, and the quantitative molecular electrostatic potential surface is displayed with color: red indicates the negative regions and
The interactions with normalized contact distance in crystal structure shorter than the sum of the corresponding van der Waals radii of the atoms, are highlighted by red spots and mapped with the corresponding van der Waals radii of the atoms, are highlighted by red spots and mapped with negative dnorm value on the Hirshfeld surface, whereas the contacts around that of van der Waals radii negative dnorm value on the Hirshfeld surface, whereas the contacts around that of van der Waals radii with zero dnorm value are plotted in white color, and the longer contacts with the positive dnorm value are represented in blue color (Figure S4 (Supplementary Materials)) [44]
Summary
Engineering well-defined molecules into specific crystal network has been one of the frontiers in material science [1,2,3]. The strength and energy of non-covalent interactions are relatively small in comparison with those of covalent bond, large numbers of non-covalent interactions play important roles in the construction of crystal frameworks and relate to various physicochemical properties, among which the most classic and widely studied intermolecular interaction is hydrogen bond [4,5,6]. Halogen bonding has been recognized as a promising alternative to hydrogen bonding in the self-assembly of a family of supramolecular architectures, especially in the fields of crystal engineering and material chemistry [15,17,18,19]. The considerable progress that has been made in different frontier sciences, to the best of our knowledge, up to the present, still no work has concerned the electronic configuration as well as the influence of halogen bonds on Schiff base complexes. Theoretical analysis suggested that XBs play a key role in linking Schiff-base 2D layers into 3D frameworks
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