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Recurrent supramolecular motifs in discrete complexes and coordination polymers based on mercury halides: prevalence of chelate ring stacking and substituent effects

Abstract

In recent years the library of crystal engineers has been enriched with a number of previously unrecognized or unnoticed intermolecular interactions such as agostic, tetrel, chalcogen, pnicogen bonding and chelate ring stacking – collectively referred to as “unconventional interactions”. Many open questions remain unaddressed regarding their ability to form synthon interactions, specificity, and cooperativity, for example with π–π stacking interactions. In this work we throw light on the formation of chelate ring stacking in metal-organic assemblies of nicotinohydrazide ligands (N′-(-(1-(2-pyridyl)ethylidene)nicotinohydrazide (HL) and N′-(phenyl(pyridin-2-yl)methylene)nicotinohydrazide (HL1)) with mercury(II) halide (HgBr2, HgI2) salts. The reaction of them produced five compounds, namely [Hg(μ-L)BrHgBr2]n (1), [Hg(μ-L1)Br]n (2), [Hg(L)I2] (3), [Hg(HL1)I2]·(CH3OH) (4), and [Hg(μ-L1)I]n (5). Crystal structure analysis reveals that chelate ring stackings are formed in four of reported metal-organic compounds, and are common also in the literature precedents. The energies of chelate ring stackings and π–π heterocycle stackings have been computed and analyzed by means of DFT calculations and results were verified using the Bader’s theory of “atoms in molecules”. Those results provide a rationale for preferential formation of both, unconventional and conventional stackings, and allow to conclude that chelate ring interaction may be considered as a synthon interaction for nicotinohydrazide metal complexes. Interpretations for packing differences imposed by the substituent effect (substitution of methyl group in HL for phenyl group in HL1) were provided based on the Hirshfeld Surface analysis and 2D fingerprint plots of reported here crystal structures.

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Publication details

The article was received on 14 Dec 2017, accepted on 09 Jan 2018 and first published on 09 Jan 2018


Article type: Paper
DOI: 10.1039/C7CE02166F
Citation: CrystEngComm, 2018, Accepted Manuscript
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    Recurrent supramolecular motifs in discrete complexes and coordination polymers based on mercury halides: prevalence of chelate ring stacking and substituent effects

    G. Mahmoudi, J. K. Zaręba, A. Bauza, M. Kubicki, A. Bartyzel, A. Keramidas, L. Butusov, B. miroslaw and A. Frontera, CrystEngComm, 2018, Accepted Manuscript , DOI: 10.1039/C7CE02166F

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