Observation of Te∙∙∙π and X∙∙∙X Bonding in para-Substituted Diphenyltellurium Dihalides, (p-Me2NC6H4)(p-YC6H4)TeX2 (X = Cl, Br, I; Y = H, EtO, Me2N)*
Jens Beckmann A B D , Dainis Dakternieks B , Andrew Duthie A , Cassandra Mitchell A and Markus Schürmann CA Centre for Chiral and Molecular Technologies, Deakin University, Geelong VIC 3217, Australia.
B Current address: Institut für Chemie, Freie Universität Berlin, 14195 Berlin, Germany.
C Lehrstuhl für Anorganische Chemie II, Universität Dortmund, 44221 Dortmund, Germany.
D Corresponding author. Email: beckmann@chemie.fu-berlin.de
Australian Journal of Chemistry 58(2) 119-127 https://doi.org/10.1071/CH04268
Submitted: 5 November 2004 Accepted: 5 January 2005 Published: 21 February 2005
Abstract
The supramolecular association of the previously described para-dimethylaminophenyl-substituted diorganotellurium dihalides (p-Me2NC6H4)2TeX2 (X = Cl (1), Br (2), I (3)) and (p-Me2NC6H4)RTeCl2 (R = Ph (4), p-EtOC6H4 (5)), was investigated by X-ray crystallography. Unlike almost all other structurally characterized diorganotellurium dihalides, (p-Me2NC6H4)2TeX2 (X = Cl (1), Br (2), I (3)) reveal no secondary Te∙∙∙X interactions, but X∙∙∙X interactions. The structure of (p-Me2NC6H4)PhTeCl2 (4) resembles that of Ph2TeCl2 and shows one secondary Te∙∙∙Cl contact, whereas (p-Me2NC6H4)(p-EtOC6H4)TeCl2 (5) exhibits neither secondary Te∙∙∙Cl nor Cl∙∙∙Cl interactions. The unusual structural characteristics of 1–5 are attributed to the occurrence of intermolecular Te∙∙∙π and π∙∙∙π contacts associated with quinoid π-electron delocalization across the para-dimethylaminophenyl (1–5) and para-ethoxyphenyl (5) groups.
Acknowledgments
The Australian Research Council is thanked for financial support. We are grateful to Professor Dr K. Jurkschat, Dortmund University, Germany, for supporting this work. Dr Jonathan White, University of Melbourne, is gratefully acknowledged for the X-ray crystallography data collection.
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* Dedicated to the occasion of the 60th birthday of Professor Wolf Walther du Mont.
† During the course of this work crystallographic data for (p-Me2NC6H4)2TeCl2 1 became available. Interestingly, in this case the refinement in the space group Pn gave better results than in P21/n. However, no structural features were discussed. For details, see ref. [9].
‡ Only one of the four crystallographically independent, albeit very similar conformers, will be discussed. Besides the orthorhombic crystal form, there was evidence for a second modification that crystallized from toluene in the monoclinic space group P21/n [cell parameters: a 9.5926(10) Å, b 5.8314(6) Å, c 17.3963(18) Å, β 93.64(1)°]. However, twinning effectively precluded the satisfactory refinement. For polymorphism and related phenomena in diorganotellurium diiodides, see ref. [11].
§ The quinoid character is defined as Q = (d1–2 + d1–6 + d3–4 + d4–5)/4 – (d2–3 + d5–6)/2, which is zero for a perfect hexagonal benzene structure, and 0.138 for a perfect quinoid structure, where d1–2 = d1–6 = d3–4 = d4–5 = 1.455 Å and d2–3 = d5–6 = 1.317 Å. An analogous parameter is defined for the second phenyl ring as Q´ = (d11–12 + d11–16 + d13–14 + d14–15)/4 – (d12–13 + d15–16)/2. The degree of pyramidality <α> is defined as the average of the three C–N–C angles.
¶ Notably, quinoid character Q is zero in p-nitroaniline hydrochloride, where resonance is made impossible.
