engleski

COMPUTATIONALLY AUGMENTED CRYSTALLOGRAPHIC STUDY OF HYDROGEN/HALOGEN BOND SWITCHING IN SELECTED CO(II) AND NI(II) PENTANE-2, 4-DIONATO COMPLEXES

The aim of crystal engineering is to design functional crystalline solids by directing the packing of their constituent molecules. The main tools used for that purpose are strong, reliable and directional interactions such as hydrogen and halogen bonds whose donors generally compete for the same acceptor sites. If we want to design complex systems with multiple, chemically different functionalities a means of predicting their linking must be developed. M.C. Etter proposed general guidelines for purely organic systems and stated that good donors will link with good acceptors according to their rank [1]. It is not a trivial matter to rank donors and acceptors but it was shown, in organic systems, that it is possible to determine their power by examining molecular electrostatic potential maps. It was shown this principle could be applied to halogen bonds in organic structures as well [2]. The question remains if those findings still hold true in the metal-organic setting due to the disruptive effect of generally present counter-ions in those systems. To give our contribution to answering that question, here we have prepared a series of CoII and NiII penatane-2, 4-dionato complexes with a series of halopyridines, halopyrazines and 5-bromopyrimidine. Halogen bonds were observed in iodopyridine derivates as well as in the bromopyridine complex with NiII. In all the other compounds C–H···O hydrogen bonds were observed as the primary interactions while the halogen was found to form halogen··· as well as type-I X···X and C–H···X interactions. DFT calculations performed on the obtained structures show that the primary motif switch from halogen to hydrogen bonds occurs in cases where the hydrogen atom present in the hydrogen bonds becomes more positive than the sigma hole on the halogen atom.

crystal engineering ; penatane-2, 4-dionato complexes ; Co(II) ; Ni(II) ; halogen bonds ; halopyridines

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