Synthesis and Crystal Structures of new Complex Salts Containing both Cationic and Anionic Tellurium ( IV ) Species : The Role of Secondary Bonds in the Arrangement of Tellurium Based Tectons

Neste trabalho divulgamos a síntese e a estrutura cristalina de uma série de três novos complexos de telúrio(IV), [Te(C 6 H 5 )(CH 3 ) 2 ]][TeX 4 (C 6 H 5 )], X = Cl (1), Br (2) ou I (3). Nesses complexos, as ligações secundárias promovem diferentes arranjos estruturais, mostrando o caráter tectônico das espécies de telúrio. Em 1 e 2, a interação Te···X promove um arranjo polimérico na forma de “zig-zag” para os ânions tetra-halofeniltelurato(IV). Em 3, as ligações secundárias Te···I induzem um arranjo diferenciado para os ânions, que estão organizados de forma antiparalela.


Introduction
Several classes of organyltellurium halide compounds are known, including species of general formula TeX 3 R, TeX 2 R 2 and TeXR 3 (R=alkyl, aryl; X=Cl, Br, I).3][4][5][6] We have been interested for some time in the synthesis and crystal structures of TeX 3 R compounds and their derivatives, such as the [TeX 4 R] -anions.These halogenated tellurates may be considered tectons (any species whose interactions are dominated by particular associative forces that induce the self-assembly of an organized network with specific architectural or functional features 7 ) where the different packing arrangements in the crystal lattice of [TeX 4 R] -salts are determined by the secondary bonds which complete the octahedral coordination at tellurium.][10][11] We now report the synthesis and crystal structures of [Te(C 6 H 5 ) (CH 3 ) 2 ][TeX 4 (C 6 H 5 )], X = Cl (1), Br (2) and I (3), complexes in which organyltellurium(IV) ion is found in both anionic and cationic species.

Experimental
All reactions were conducted under nitrogen, but recrystallizations of the complexes were done in air.Methanol was dried with Mg/I 2 and acetonitrile with CaH 2 , and both were distilled prior to use. 12 The compound iododimethylphenyltellurium(IV) was prepared according to Reid's procedure; 13 the analogous chloride and bromide derivatives were prepared by ion exchange with the appropriate silver halide in hot methanol.Trihalophenyltellurium(IV) compounds were prepared following literature procedures. 14Melting points were recorded in a Microquimica equipment and are uncorrected.Elemental analyses (C, H) were performed at the Microanalytical Laboratory of the Chemistry Institute -University of São Paulo.

H and 125 Te NMR
The NMR spectral data were obtained in a Varian Mercury Plus 7.05 T spectrometer with 300.07 MHz ( 1 H) and 94.74 MHz ( 125 Te).The samples were dissolved in a 9:1 mixture of acetone-d 6 and DMSO-d 6 , respectively.The solutions were measured in NMR tubes of 5 mm, at 300 K.The 1 H NMR chemical shifts are relative to Si(CH 3 ) 4 as internal reference.The 125 Te NMR spectra were taken with reference to Te(CH 3 ) 2 .A capillary containing Te 2 (C 6 H 5 ) 2 dissolved in CDCl 3 (δ 450) was used as external reference.By convention, the chemical shift is positive when the resonance occurs at higher frequency than that of the reference.

Crystallography
X-ray data were collected on a Bruker X8 APEX II diffractometer using Mo Kα radiation (0.71073 Å).The crystallographic structures of 1, 2 and 3 were solved by direct methods (SHELXS-97). 15Refinements were carried out with the SHELXL-97 package. 16All refinements were made by full-matrix least-squares on F 2 with anisotropic displacement parameters for all non-hydrogen atoms.Hydrogen atoms were included in the refinement in calculated positions.

Results and Discussion
The new tellurium(IV) complexes were obtained in good yields by the reactions of methanolic solutions of the halodimethylphenyltellurium(IV) with the appropriate trihalophenyltellurium(IV) to afford microcrystalline solids.In order to examine the occurrence and extent of Te•••X secondary bonds, and the effect of these interactions on the environment at tellurium atoms, crystallographic analyses were carried out on single crystals of the products obtained from the slow evaporation of acetonitrile solutions.Crystal data and details of the data collection are given in Table 1.Solution NMR spectra confirm the ionic nature of the product.
The solution 125 Te NMR spectra show two peaks for each compound.The low frequency peak, around δ 580, is attributed to the cationic [Te(C 6 H 5 )(CH 3 ) 2 ] + species, which corresponds well to the value found for [Te(C 6 H 5 ) (CH 3 ) 2 ]I (δ 550 in DMSO). 17The lower field peak, attributed to the anionic [TeX 4 Ph] -species, show chemical shifts at δ 1234.81,1203.87 and 951.08 for 1, 2 and 3 respectively.The chlorine atom, being the most electronegative of the halides, deshields best the tellurium atom. 17he crystal structures of 1, 2 and 3 confirm that the compounds are essentially ionic.Within the crystals, the packing is determined by Te•••X secondary bonds between anion-anion and cation-anion pairs.The primary coordination geometries of the tellurium cations, as well as the tellurate anions, are similar in all structures.The geometry of the tellurium cation is trigonal pyramidal while the tellurate anion is squarepyramidal.When the two Te•••X secondary bonds are considered, the tellurium cation has a distorted square pyramidal geometry with the phenyl group in the apical position.The resulting geometry is very similar to that of an equivalent tellurate anion.When the secondary bonds are considered for the tellurate anion, the resulting geometry is a distorted octahedron, with the secondary bond in the trans position to the phenyl group, forming a structure similar to an equivalent tellurate dianion.Table 2 shows selected primary and secondary bonding distances within the compounds.

Figure 1 .
Figure 1.General representation for the structures of 1 and 2, emphasizing the zig-zag architecture along the b axis promoted by the secondary bonds Te•••X (X=Cl, Br).Symmetry operations to generate equivalent atoms: '= 1-x; -0.5+y; 0.5-z.

Table 2 .
Selected bond lengths.The covalent bonds are represented by ⎯ and the secondary bonds by •••.Symmetry operations are depicted under the respective columns

Table 1 .
Crystallographic data of the new complexes synthesized