Elsevier

Journal of Solid State Chemistry

Volume 204, August 2013, Pages 128-135
Journal of Solid State Chemistry

Intermolecular interactions between imidazole derivatives intercalated in layered solids. Substituent group effect

https://doi.org/10.1016/j.jssc.2013.05.029Get rights and content

Highlights

  • Imidazole derivatives intercalation compounds.

  • Intermolecular interaction between intercalated imidazole derivatives.

  • Hybrid inorganic–organic solids.

  • Pi–pi interactions and ferromagnetic coupling.

  • Dipolar and quadrupolar interactions between intercalated imidazole derivatives.

Abstract

This study sheds light on the intermolecular interactions between imidazole derive molecules (2-methyl-imidazole, 2-ethyl-imidazole and benzimidazole) intercalated in T[Ni(CN)4] layers to form a solid of formula unit T(ImD)2[Ni(CN)4]. These hybrid inorganic–organic solids were prepared by soft chemical routes and their crystal structures solved and refined from X-ray powder diffraction data. The involved imidazole derivative molecules were found coordinated through the pyridinic N atom to the axial positions for the metal T in the T[Ni(CN)4] layer. In the interlayers region ligand molecules from neighboring layers remain stacked in a face-to-face configuration through dipole–dipole and quadrupole–quadrupole interactions. These intermolecular interactions show a pronounced dependence on the substituent group and are responsible for an ImD-pillaring concatenation of adjacent layers. This is supported by the structural information and the recorded magnetic data in the 2–300 K temperature range. The samples containing Co and Ni are characterized by presence of spin–orbit coupling and pronounced temperature dependence for the effective magnetic moment except for 2-ethyl-imidazole related to the local distortion for the metal coordination environment. For this last one ligand a weak ferromagnetic ordering ascribed to a super-exchange interaction between T metals from neighboring layers through the ligands π–π interaction was detected.

Graphical abstract

In the interlayers region imidazole derivative molecules are oriented according to their dipolar and quadrupolar interactions and minimizing the steric impediment.

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Introduction

Pi–pi interaction in aromatic and heteroaromatic molecules has relevant importance in organic and biological chemistry, both in solution and in solid state [1]. It contributes to the stability of DNA and proteins, to the drug effect in biological systems and to the cohesive forces in organic crystals [1], [2], [3], [4], [5].This type of interaction is of electrostatic nature and it is established between charge distributions of neighboring molecules. For benzene, for instance, the most stable configuration is that where neighboring molecules are stacked according to edge-to-face configuration [1], [2]. The incorporation of heteroatoms in such six member ring modifies the charge distribution and, in consequence, the molecule quadrupole moment. For pyridine molecules, for instance, the most stable relative orientation corresponds to an opposite face-to-face configuration related to both, dipole–dipole and quadrupole–quadruple interactions [6]. This illustrates the role of heteroatoms in the electrostatic intermolecular interactions. An analogue effect has the presence of substituent group in both, aromatic and heteroaromatic molecules [1].

Such interaction remains poorly documented for organic molecules intercalated in layered solids, where valuable experimental information on interactions of the involved molecules can be obtained. Layered materials of formula unit T[M(CN)4] where M is Ni, Pd, or Pt and T is a divalent transition metal, form a family of 2D inorganic solids with available axial coordination sites for the metal T in the layer. Since the metal T centers are distant about 10 Å, a regular 2D grid of coordination sites for the organic ligands incorporation is formed. From the intercalation of ligand molecules with only one charge donating atom to be coordinated to these metal centers, in the interlayers region a system of hanging molecules with possibility of interactions between them can be obtained. For heteroaromatic molecules such interactions will be dominated by electrostatic forces of dipolar and quadrupolar nature and, in consequence, with possibility of π–π coupling between them. Thus, neighboring layers would be communicated through such π–π coupling. In a previous study we have considered the intercalation of imidazole molecules between T[Ni(CN)4] layers where that molecule is found coordinated through its pyridinic N atom to the metal T at the layer [7]. In the interlayer region imidazole molecules coordinated to neighboring layers remain stacked in a face-to-face configuration to form a pillar chain by means of dipole-dipole and quadrupole–quadrupole interactions. The existence of π–π coupling between neighboring molecules becomes evident by the presence of a low temperature ferromagnetic interaction for the involved T metals from neighboring layers. In the absence of that π–π coupling, no ferromagnetic ordering between T metal centers could be present. In this contribution three imidazole derivatives (ImD), 2-methyl-imidazole (MeIm), 2-ethyl-imidazole (EtIm), and benzimidazole (BzIm), were intercalated between T[Ni(CN)4] layers in order to shed light on the substituent group effect in the resulting intermolecular interactions. To the best of our knowledge, no previous reports on the preparation and study of the resulting series of hybrid solids and related intermolecular interactions are available.

Section snippets

Experimental

The samples to be studied were prepared by the precipitation method from aqueous solutions. The involved T2+ metals were added, drop by drop under stirring, to a previously prepared solution of the organic ligand (ImD) and of K2[Ni(CN)4].On aging for at least 48 h a fine precipitate is formed which is then separated by centrifugation from the mother liqueur and washed several times with distilled water in order to remove all the accompanied species and finally dried in air until it had constant

Nature of the formed Hybrid solids

According to the experimental evidence obtained from EDS, IR, UV–vis and TG data, for the considered imidazole derivatives, hybrid solids of formula unit T(ImD)2[Ni(CN)4] are formed, where the metal T2+ is found with pseudo-octahedral coordination to four N atoms from the anionic unit, [Ni(CN)4]2−, and to two axial pyridinic N atoms from organic ligands while the Ni atom preserves its square planar coordination.

The recorded IR spectra for the obtained powders, below 2000 cm−1, can be interpreted

Conclusions

Imidazole derivative molecules (2-methyl-imidazole, 2-ethyl-imidazole and benzimidazole) intercalated between T[Ni(CN)4] layers were found coordinated through the pyridinic N atom to the metal T in the layer but at same time interacting among them by dipole–dipole and quadrupole–quadrupole interactions. Such interactions support the formation of a system of pillars which remains interacting to form a sub-structure of chains in the interlayers region. The spatial ligand orientation and the

Supplementary information

CCDC files containing the supplementary crystallographic datafor 903527: Mn(MeIm)2[Ni(CN)4]; 903525: Co(MeIm)2[Ni(CN)4];903530: Ni(MeIm)2[Ni(CN)4]; 903524: Co(EtIm)2[Ni(CN)4]; 903529: Ni(EtIm)2[Ni(CN)4]; 903526: Mn(BzIm)2[Ni(CN)4]; 903523: Co(BzIm)2[Ni(CN)4]; and 903528: Ni(BzIm)2[Ni(CN)4]. These data can be obtained from http://www.ccdc.cam.ac.uk/conts/retrieving.html, and also from the CambridgeCrystallographic Data Centre, 12 UnionRoad, Cambridge CB21EZ, UK; fax:(+44) 1223-336-033; or

Acknowledgments

This study was partially supported by the Projects CONACyT-2009-01-129048, 2010-01-155413, 2011-01-166387, 2011-01-174247, 2012- 193850, and FOINS I0-296-2012. The access to Laboratorio Nacional de Luz Sıncrotron (LNLS) at Campinas, SP, Brazil, is greatly recognized.

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