**3. Supramolecular arrangements in organotellurium compounds**

#### **3.1 Method**

A CSD search considering organic structures with deposited atomic coordinates, with R factor < 0.1, and without disorder involving Te and X was undertaken. After removing multiple entries of the same structure, a new search was carried out in order to retrieve structures showing intermolecular Te···X contacts. According to the results presented in section 2, a cut-off of Σ rvdW + 10% Å was considered. In these structures, supramolecular patterns were investigated using the program Mercury (Version 2.4) (Macrae et al., 2008). A set of 616 organotellurium structures having halogen atoms was collected. The greater part of them, 490 (80%), contain the Te-X unit, *i.e.* at least one tellurium-halogen covalent bond. Four groups can be considered: (i) structures containing tellurium atoms with only one halogen atom bonded to it, *i.e.* having the C-Te(-X)1 unit, (ii) structures containing tellurium atoms bonded to only two halogen atoms, *i.e.* having the C-Te(-X)2 unit, (iii) structures containing tellurium atoms with only three halogen atoms bonded to it, *i.e.* having the C-Te(-X)3 unit, and (iv) structures containing tellurium atoms bonded to four halogen atoms, *i.e.* having the C-Te(-X)4 unit. A fifth group (v) includes the remaining 126 structures of organotellurium compounds having halogen atoms but not Te-X units: structures with C-Te(-X)0.

### **3.2 Structures of compounds containing the Te(-X)1 unit**

116 Current Trends in X-Ray Crystallography

The existence of intermolecular Te···X interactions is frequent in crystal structures of organotellurium compounds containing halogen atoms. Using the values showed in Table 1, the estimation of structures with Te···X interactions is about 60%. Of the total number of structures showing Te···X contacts, 13% of them exhibit Te···F interaction, 38%, Te···Cl,

> **Te···F** 3.26(11) 2.96, 3.80 10 **Te-F** 1.989(4) 1.95, 2.02 43

> **Te···Cl** 3.672(15) 3.42, 3.97 191 **Te-Cl** 2.521 (3) 2.47, 2.61 546

> **Te···Br** 3.88 (2) 3.56, 4.25 121 **Te-Br** 2.693(5) 2.63, 2.79 234

> **Te···I** 3.95 (2) 3.67, 4.37 203 **Te-I** 2.944(4) 2.87, 3.04 383

Table 1. Te···X secondary and Te-X covalent bond distances (Å) in organotellurium crystal structures. The sum of van der Waals radii (Bondi, 1964), Σ rvdW, is also included. d: mean

A CSD search considering organic structures with deposited atomic coordinates, with R factor < 0.1, and without disorder involving Te and X was undertaken. After removing multiple entries of the same structure, a new search was carried out in order to retrieve structures showing intermolecular Te···X contacts. According to the results presented in section 2, a cut-off of Σ rvdW + 10% Å was considered. In these structures, supramolecular patterns were investigated using the program Mercury (Version 2.4) (Macrae et al., 2008). A set of 616 organotellurium structures having halogen atoms was collected. The greater part of them, 490 (80%), contain the Te-X unit, *i.e.* at least one tellurium-halogen covalent bond. Four groups can be considered: (i) structures containing tellurium atoms with only one halogen atom bonded to it, *i.e.* having the C-Te(-X)1 unit, (ii) structures containing tellurium atoms bonded to only two halogen atoms, *i.e.* having the C-Te(-X)2 unit, (iii)

value; σ: mean standard deviation; q10, q90: 10% and 90% percentiles; n: number of observations; covalent bond distances have been obtained in this work from

**3. Supramolecular arrangements in organotellurium compounds** 

 **d(**σ**) q10, q90 n** 

20%, Te··· Br and 29%, Te···I.

Σ **rvdW** 3.53

Σ **rvdW** 3.81

Σ **rvdW** 3.91

Σ **rvdW** 4.04

organotellurium(IV) crystal structures from CSD

**3.1 Method** 

Te(-X)1 unit (tellurium atom bonded to one halogen only), is a very simple unit and it is a good starting point to study supramolecular arrangements *via* Te···X contacts. Two arrangements are the more habitual in this group: (a) dimeric assembly, and (b) simple chain (Figure 2, Table 2).

Fig. 2. Main supramolecular arrangements of compounds containing the Te(-X)1 unit


Table 2. Summary of structures containing the Te(-X)1 unit

a. In the dimer, the two Te-X rods are bonded by two Te···X secondary bonds. The majority is centrosymmetric, with X···Te-X angles around 90º.

In C-Te(II)-X (X = Cl, Br, I) compounds, dimers were observed These compounds are not stable and the secondary bond stabilizes them. A new pattern is observed when weaker secondary bonds are considered (contact distances < Σ rvdW + 20%): a chain of dimers like a zigzag ladder (Figure 3) where two neighbour dimers are related by a symmetry centre. In this way, three TeX distances are present, being the Te-X rod length the shortest one. A great dispersion of distances was observed, not only in secondary bonds but in the "primary" bond as well.

Dimeric arrays were also observed in some molecules containing several Te-X units. In these cases the covalent skeleton increases the dimensionality of the whole arrangement. In this way, if two Te-X units are present, the structure contains chains, if there are four Te-X units by molecule, a sheet of dimers is formed (Figure 4).

b. In the simple chain, every rod is bonded to its neighbour using only one secondary bond. In some cases the chain is planar and neighbour rods are equivalent by translation. In the other cases, chains are generated by a screw binary axis or by a glide plane.

Supramolecular Arrangements in Organotellurium Compounds *via* Te**···**Halogen Contacts 119

*b*)

simple chain (SC)

*d1*

*d1 d2*

*d1*

*d1 d1*

*d1*

*d1 d2 d2*

*d1*

*d2*

sheet (S)

1d-polymer (RC-1d)

2d-polymer (RC-2d)

chain of dimers (RC-CD)

*f*)

dimer (D)

*d1*

*d2 d1*

*d1*

*d2*

*d1*

*c*) 4-membered ring chains:

*d1*

*d2*

*d2*

*d1*

*d1*

*d1*

tetramer (T)

*d*)

*a*)

Fig. 6. Main supramolecular arrangements of compounds containing the Te(-X)2 unit

3D-network (N)

*e*)

Fig. 3. Chain of dimers like a zigzag ladder (*d1* > *d2*)

Fig. 4. Examples of chain and sheet resulting from the combination of dimers and a covalent skeleton

#### **3.3 Structures of compounds containing the Te(-X)2 unit**

The most populated group of organotellurium compounds contains the C-Te(-X)2 unit (only two halogen atoms bonded to tellurium). A lot of them have a C2TeX2 core showing a pseudotrigonal bipyramidal disposition with the halogen atoms in axial positions and a lone electron pair in an equatorial site (Figure 5).

Fig. 5. Pseudotrigonal bipyramidal coordination frequent in R2TeX2 compounds

A great diversity of arrangements is present in this group. Three of such arrangements are clearly the most usual: (a) dimer, (b) simple chain, and (c) chain of four-sided rings sharing opposite vertices. Other three arrangements, with more complicated patterns of secondary bonds, have also significant populations: (d) tetramer, (e) sheet, and (f) 3D-network (Figure 6, Table 3).

Fig. 4. Examples of chain and sheet resulting from the combination of dimers and a covalent

The most populated group of organotellurium compounds contains the C-Te(-X)2 unit (only two halogen atoms bonded to tellurium). A lot of them have a C2TeX2 core showing a pseudotrigonal bipyramidal disposition with the halogen atoms in axial positions and a lone

Fig. 5. Pseudotrigonal bipyramidal coordination frequent in R2TeX2 compounds

A great diversity of arrangements is present in this group. Three of such arrangements are clearly the most usual: (a) dimer, (b) simple chain, and (c) chain of four-sided rings sharing opposite vertices. Other three arrangements, with more complicated patterns of secondary bonds, have also significant populations: (d) tetramer, (e) sheet, and (f) 3D-network

Fig. 3. Chain of dimers like a zigzag ladder (*d1* > *d2*)

*d1 d2*

*d1 d2*

**3.3 Structures of compounds containing the Te(-X)2 unit** 

REDXEE HOJJEV01

electron pair in an equatorial site (Figure 5).

skeleton

(Figure 6, Table 3).

Fig. 6. Main supramolecular arrangements of compounds containing the Te(-X)2 unit

Supramolecular Arrangements in Organotellurium Compounds *via* Te**···**Halogen Contacts 121

e. Five structures with infrequent spatial groups (*Fdd*2 and *I*41/*acd*) adopt a symmetric polar 3D-network where all secondary bonds are equal. Every Te(-X)2 rod is bonded to

f. A sheet with two secondary bond distances and where every rod is bonded to three neighbours is relatively usual. This arrangement can be described in two ways, depending on the distance ratio. In two structures, the best description is to consider them as centrosymmetric dimers (type (a)) bonded to four neighbours, involving the two Te and the two distant halogens of the dimer. For another two structures it is better to think in simple chains (type (b)) where every rod is bonded to another rod of a neighbouring chain by means of two Te···X bonds. Anyway, 4- and 12-membered rings

g. Finally, four pairs of structures were found, each pair with its own arrangement: two

Fig. 7. Less frequent supramolecular arrangements of compounds containing the Te(-X)2

This unit shows a T disposition derived of the tendency of halogen atoms to occupy axial positions (angle X-Te-X near to 180º). The dimeric arrangement (a) is adopted by most structures. The simple chain (b) and the chain of 4-membered rings (c) are present but are

Sd

four neighbours, with two bonds from Te and one from every halogen.

tetramers found are centrosymmetric.

chains and two sheets (Figure 7).

Cc Cd

unit: Cc and Cd chains; Sc and Sd sheets

Sc

much less usual (Figure 8, Table 4).

**3.4 Structures of compounds containing the Te(-X)3 unit** 

are present.

This arrangement implies the existence of two non-equivalent rods, thus forcing the structure to have more than one molecule in the asymmetric unit (Z' > 1). All the


Table 3. Summary of structures containing the Te(-X)2 unit

a. Dimers formed by Te(-X)2 have the same connectivity as those described for Te(-X)1, *i.e.* two Te···X secondary bonds, and the majority are also centrosymmetric. Non centrosymmetric dimers are almost planar in absence of other interactions.

Most X-Te···X angles are lesser than 90º, *i.e.* two rods are "moved away" relative to the rectangular disposition. This is a small difference respect to the Te(-X)1 dimers, where deviation from 90º were present in both directions. Only three dimers of angular Te(-X)2 were found, centrosymmetric all of them.


The three types of chain have also different internal symmetry. In the chains of dimers, 4-membered rings are centrosymmetric (rhomboids) and are disposed in zigzag. In six of the more symmetric polymers, there are symmetry centres in the middle of all rings, and moreover, binary axes, perpendicular to the chain direction, through the Te atoms, and glide planes. One symmetric polymer is helical, generated by a screw 4-fold axis, vs the zigzag disposition found in the other 6 structures. At last, polymers with two different secondary bonds between neighbours are generated by glide planes and adopt a zigzag conformation.

d. Another finite arrangement of Te(-X)2 is a cyclic tetramer, where a Te(-X)2 unit is bonded to every neighbour with two secondary bonds in a step-like manner. The tetramer has two different types of tellurium atoms: the two "middle" Te atoms defining a Te2X2 ring are different from the two "terminal" Te atoms placed out of the Te2X2 ring.

**Dimer** 2 18 7 18 45 **Simple chain** 0 17 10 4 31 **Chain of 4-membered rings** 2 11 5 6 24 **Tetramer** 0 5 1 3 9 **Sheet** 0 2 0 2 4 **3D-Network** 0 1 2 2 5 **Less frequent arrangements** 2 1 2 3 8 **Total** 6 55 27 38 126

a. Dimers formed by Te(-X)2 have the same connectivity as those described for Te(-X)1, *i.e.* two Te···X secondary bonds, and the majority are also centrosymmetric. Non

b. The Te(-X)2 simple chain is also referable to Te(-X)1 simple chains but here, planar chains are absent, the reason being that planar chains have the translation as unique symmetry element. In the case of Te(-X)2, this would imply the presence of an additional Te···X contact leading to a different kind of chain. So, rods in Te(-X)2 simple chains are

c. The third most common arrangement is a di-bridged chain made by 4-membered rings sharing opposite vertices (Te atoms). Three types of chain (polymer) can be considered when Te···X distances are analyzed. So, if 4-membered rings are not equal (6 structures), a dimer is present and this type of polymer will be named chain of dimers. If all 4-membered rings are equal, the basic unit in the polymer is an X-Te-X rod and two cases are possible. In the more symmetric one (7 structures), the two secondary bonds between neighbour rods are equal while in the less symmetric one (11 structures) are not. These two types of polymer will be named 1d- and 2d-polymer respectively. The three types of chain have also different internal symmetry. In the chains of dimers, 4-membered rings are centrosymmetric (rhomboids) and are disposed in zigzag. In six of the more symmetric polymers, there are symmetry centres in the middle of all rings, and moreover, binary axes, perpendicular to the chain direction, through the Te atoms, and glide planes. One symmetric polymer is helical, generated by a screw 4-fold axis, vs the zigzag disposition found in the other 6 structures. At last, polymers with two different secondary bonds between neighbours are generated by glide planes and adopt

d. Another finite arrangement of Te(-X)2 is a cyclic tetramer, where a Te(-X)2 unit is bonded to every neighbour with two secondary bonds in a step-like manner. The tetramer has two different types of tellurium atoms: the two "middle" Te atoms defining a Te2X2 ring are different from the two "terminal" Te atoms placed out of the

Most X-Te···X angles are lesser than 90º, *i.e.* two rods are "moved away" relative to the rectangular disposition. This is a small difference respect to the Te(-X)1 dimers, where deviation from 90º were present in both directions. Only three dimers of angular

centrosymmetric dimers are almost planar in absence of other interactions.

Table 3. Summary of structures containing the Te(-X)2 unit

Te(-X)2 were found, centrosymmetric all of them.

equivalent by screw binary axes or by glide planes.

a zigzag conformation.

Te2X2 ring.

**F Cl Br I Total** 

This arrangement implies the existence of two non-equivalent rods, thus forcing the structure to have more than one molecule in the asymmetric unit (Z' > 1). All the tetramers found are centrosymmetric.


Fig. 7. Less frequent supramolecular arrangements of compounds containing the Te(-X)2 unit: Cc and Cd chains; Sc and Sd sheets

#### **3.4 Structures of compounds containing the Te(-X)3 unit**

This unit shows a T disposition derived of the tendency of halogen atoms to occupy axial positions (angle X-Te-X near to 180º). The dimeric arrangement (a) is adopted by most structures. The simple chain (b) and the chain of 4-membered rings (c) are present but are much less usual (Figure 8, Table 4).

Supramolecular Arrangements in Organotellurium Compounds *via* Te**···**Halogen Contacts 123

These compounds are ionic (or zwitterionic) and the coordination around the Te can be described as a tetragonal pyramid with the halogens and the tellurium in the basal plane and the carbon in the apical position of the pyramid. Two supramolecular patterns are

Fig. 9. Main supramolecular arrangements of compounds containing the Te(-X)4 unit

**Dimer** 0 6 4 6 16 **Simple chain** 0 2 3 2 7 **Total** 0 8 7 8 23

a. Dimers. As in Te(-X)1, Te(-X)2 and Te(-X)3, dimers contain two secondary bonds. These bonds complete an octahedral coordination for every Te. All dimers are

b. Simple chains. Again, the secondary bond completes the octahedral coordination of tellurium atom. As in Te(-X)2 and Te(-X)3 chains, units in Te(-X)4 simple chains are

This group is very heterogeneous from a chemical point of view, nevertheless some subsets can be established (Figure 10). A first subset (12 structures) was considered where neutral

This subset can be considered a general case of the compounds studied in the previous sections: now the tellurium atom and the halogens are separated by more than one covalent bond, hereinafter Te(---X)n. Therefore some above described arrangements were also found here: dimer (4 structures), simple chain (2 structures), and chain of dimers (2 structures). In a second subset of 11 neutral ditellurides, known patterns were also found in more than half the cases, considering them as X---Te-Te---X. Every Te---X unit affords its own arrangement of secondary bonds: dimers (3 structures), and simple chains (3 structures).

**F Cl Br I Total** 

two Te···X distances (glide planes).

*a*) *b*)

**3.5 Structures of compounds containing the Te(-X)4 unit** 

relevant: (a) dimers and (b) simple chains (Figure 9, Table 5).

dimer (D) simple chain (SC)

Table 5. Summary of structures containing the Te(-X)4 unit

equivalent by screw axes or by glide planes.

molecules contain one Te and halogen atoms.

centrosymmetric except one with a binary axis instead.

**3.6 Structures of compounds without Te-X units [Te(-X)0]** 

dispositions can be adopted: chain of dimers (centrosymmetric rings) and polymer with

Fig. 8. Main supramolecular arrangements of compounds containing the Te(-X)3 unit: dimer (D); simple chain involving only axial halogen atoms (SC) or equatorial halogen atoms (SCeq); 4-membered ring chain: chain of dimers (RC-CD), 2d-polymer involving only axial halogen atoms (RC-2d), and 2d-polymer involving equatorial (RC-2d-eq) halogen atoms


Table 4. Summary of structures containing the Te(-X)3 unit


dispositions can be adopted: chain of dimers (centrosymmetric rings) and polymer with two Te···X distances (glide planes).
