Elsevier

Inorganica Chimica Acta

Volume 330, Issue 1, 13 March 2002, Pages 149-154
Inorganica Chimica Acta

Synthesis, and crystal and molecular structures of the triflato and trifluoroacetato complexes of zinc, Zn(O3SCF3)2(DME)2 and [Zn(O2CCF3)2(DME)]n

This article is dedicated to the memory of the late Professor Luigi M. Venanzi, an outstanding scientist and a good friend
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Abstract

Anhydrous Zn(O3SCF3)2 and Zn(O2CCX3)2, X=F, Cl, Br were obtained in substantially quantitative yields from ZnO (or ZnEt2 in the case of the bromide derivative) and a mixture of the corresponding acid and anhydride in heptane as medium. The reactions are rapid and moderately exothermic. Recrystallization of the triflate and trifluoroacetate complexes from dimethoxyethane (DME) produced single crystals of Zn(O3SCF3)2(DME)2 (1) and [Zn(O2CCF3)2(DME)]n (2) suitable for X-ray diffraction studies. In both compounds zinc is hexacoordinated with a pseudo-octahedral geometry. Compound 1 is constituted by mononuclear molecules with terminal monodentate O3SCF3 ligands in trans position. A polynuclear chain structure was found for 2 with zinc atoms joined alternatively by triple and single carboxylato bridges, and with bidentate terminal DME.

The synthesis, crystal and molecular structures of the title compounds are reported. In the mononuclear triflato complex the zinc atom is pseudo-octahedral with two bidentate DME ligands and two monodentate triflato groups. In DME solution, the trifluoroacetato ligand is displaced by triflic acid.

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Introduction

The chemistry of weakly coordinating anions is a subject of major current interest for several reasons. In this category, fluorinated anions are mostly considered and several review-articles have been devoted to this important class of ligands [1], [1](a), [1](b), [1](c), [1](d), [1](e). Fluorinated ligands may vacate a coordination position, thus becoming useful in catalytic cycles. Earlier work from these Laboratories has reported the formation of trifluoroacetato complexes of vanadium(II) [2] and manganese(II), two polynuclear linkage isomers of formula [Mn(CF3COO)2(THF)2]n being isolated and structurally characterized [3]. Among homoleptic compounds (i.e. containing a homogeneous set of anionic ligands in a number corresponding to the oxidation state of the central metal atom), mention should be made of the recently acquired copper(II) derivative [Cu(CF3COO)2]n [4], [4](a), [4](b). As far as triflato complexes are concerned, a literature survey has shown that homoleptic, non-ionic, structurally characterized derivatives are still rather limited in number, examples being the derivatives of iron(II) [5], [5](a), [5](b), [5](c), [5](d), silver(I) [6], [6](a), [6](b), [6](c), [6](d), [6](e), [6](f), copper(I) [7], [7](a), [7](b), copper(II) [8], cadmium [9], and cobalt(II) [10]. An examination of the literature showed that the trifluoroacetato complex of zinc(II), Zn(O2CCF3)2py2, of unknown structure, has been prepared [11]. Moreover, although zinc(II) triflate is commercialized, and used, for example, in the synthesis of dithioketals [12], its preparation has been described only briefly in the scientific literature [13], [13](a), [13](b). Mention has also been made that the tribromoacetato complex of zinc with nitrogen donors is unstable. In this paper, we report the synthesis of the unsolvated triflato-, and trifluoroacetato complexes of zinc(II) and the structural study of the corresponding dimethoxyethane (DME) adducts.

Section snippets

General

All preparations were carried out using standard Schlenk techniques. All solvents were freshly distilled over appropriate drying agents. The compounds reported in this paper are not sensitive to dioxygen but reactions and manipulations were carried out under dry dinitrogen. Trifluoromethanesulfonic anhydride, trihaloacetic anhydride (X=F, Cl), trifluoromethanesulfonic acid, trihaloacetic acid (X=F, Cl) and ZnO were commercial products (Aldrich), used without further purification. Tribromoacetic

Results and discussion

The anhydrous triflato- and trifluoroacetato derivatives of zinc(II) were prepared from ZnO and the appropriate acid in the presence of the corresponding anhydride in order to eliminate adventitious water and that produced in the reaction (, ). The reactions were carried out in heptane as medium with an excess of both the acid and the anhydride. The products were separated by filtration and found to be analytically pure.ZnO+2(HO)SO2CF3→H2O+Zn(O3SCF3)2ZnO+2CX3COOH→H2O+Zn(CX3COO)2(X=F, Cl, Br)

It

Supplementary material

Crystallographic data including atomic coordinates, thermal parameters, full lists of bond distances and angles and details of structure determination have been deposited in the form of CIF files with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 170233 for Zn(OSO2CF3)2[(CH2)2(OMe)2] and 170234 for catena complex Zn(OCOCF3)2[(CH2)2(OMe)2]. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:

Acknowledgements

This work was supported by the Ministero dell' Università e della Ricerca Scientifica, MURST, Progetti di Rilevante Interesse Nazionale 2000-1. We thank Dr. Riccardo Po of Enichem-IGD, Novara, for helpful discussions.

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