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)

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doi:10.1071/CH04268

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, Markus Schürmann ^C

^A 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





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Australian Journal of Chemistry 58(2) 119–127 http://dx.doi.org/10.1071/CH04268
Submitted: 5 November 2004 Accepted: 5 January 2005 Published online: 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.

^* 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 = (d_1–2 + d_1–6 + d_3–4 + d_4–5)/4 – (d_2–3 + d_5–6)/2, which is zero for a perfect hexagonal benzene structure, and 0.138 for a perfect quinoid structure, where d_1–2 = d_1–6 = d_3–4 = d_4–5 = 1.455 Å and d_2–3 = d_5–6 = 1.317 Å. An analogous parameter is defined for the second phenyl ring as Q´ = (d_11–12 + d_11–16 + d_13–14 + d_14–15)/4 – (d_12–13 + d_15–16)/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.