Review
Stereochemical activity of lone pairs of electrons and supramolecular aggregation patterns based on secondary interactions involving tellurium in its 1,1-dithiolate structures

https://doi.org/10.1016/j.ccr.2009.09.007Get rights and content

Abstract

A survey of the crystallographic literature of tellurium(II)/(IV) 1,1-dithiolates (dithiocarbamate, xanthate, dithiophosphate, or dithiophosphinate) is presented. Coordination numbers range from a low of three in some organotellurium(II) 1,1-dithiolates to a high of eight in the binary tellurium(IV) dithiocarbamates. The coordination geometries are rich and varied due to the stereochemical influence exerted by up to two lone pairs of electrons and the penchant of tellurium to increase its coordination number by forming secondary Te⋯X interactions, where X = sulphur, halide, tellurium, oxygen, and, in one case, a π system defined by a four-membered TeS2C chelate. Stereochemical roles of the lone pairs of electrons are always evident in the tellurium(II) structures. By contrast, a stereochemical position is not always evident for the lone pair of electrons in the tellurium(IV) derivatives, in particular in circumstances where the tellurium centre has a high coordination number. Supramolecular aggregation mediated by Te⋯X secondary interactions often leads to the formation of dimeric aggregates but sometimes to supramolecular polymers, and rarely three-dimensional networks. Comparisons between closely related structures clearly indicate that the dithiocarbamate ligand is a more effective chelating ligand compared with the other 1,1-dithiolate ligands covered in this survey. This difference in coordinating ability is clearly correlated with the observation that non-dithiocarbamate structures are more likely to form high-dimensional supramolecular architectures.

Introduction

Metal 1,1-dithiolate compounds continue to attract significant attention owing to their many and varied applications ranging from agriculture, to medicine, and organic synthesis; see Fig. 1 for chemical structures of selected examples of 1,1-dithiolate anions relevant to the present review. In agriculture, a prominent example is the continued use of the pesticide Mancozeb®, an ethylenebis(dithiocarbamate) containing manganese and zinc [1], [2], [3]. In medicine, the aldehyde dehydrogenase inhibitor tetraethylthiuram disulfide (Disulfiram, Antabuse®), an oxidation product of the diethyldithiocarbamate anion, is still used as a treatment for chronic alcoholism and, when co-administered with metals, as an anti-cancer agent [4], [5], [6]. In addition, there is an ever increasing number of metal compounds being evaluated for biological activity with gold [7], [8], [9] and bismuth [10] dithiocarbamates, in particular, attracting attention as potential anti-tumour agents. The 1,1-dithiolate anions themselves may be used in organic synthesis [11], [12], [13]. Many of their metal compounds serve as highly efficient precursors for metal sulphide nanoparticle generation [14], [15], [16], [17], [18]. The 1,1-dithiolate ligands are relatively easy to prepare and once made, many of their metal complexes are stable [19]. As such, and given the practical importance of metal 1,1-dithiolates, crystallographic studies are a favoured mode of structural characterisation [20], [21], [22], [23]. Consequently, the relative ease of crystallisation of metal dithiolate complexes has resulted in their being exploited in the rapidly emerging field of crystal engineering, i.e. in the realm of both transition metal [24], [25], [26], [27] and main group element chemistry [28], [29], [30], [31], [32], [33]. In a related theme and as an example of “data mining”, the availability of a relatively large number of structures has allowed structural correlations to be made whereby different types of intermolecular interactions are investigated in closely related structures. Specifically, the prevalence of secondary bonding interactions operating in the crystal structures of main group element compounds has been investigated [34], [35], [36], [37]. Secondary interactions have been long recognized as important in stabilising crystal structures, see the seminal discussions of Alcock [38], [39], and in their simplest form may be regarded as solid-state Lewis acid (metal centre)⋯Lewis base (sulphur or other donor atom) interactions. The aforementioned systematic surveys have shown that it is possible to control the formation of secondary interactions by varying the steric bulk of organic groups, either/or in a remote substituent of a ligand or directly bound to the metal centre, as in organometallic derivatives [34], [35], [36], [37]. It is the determination of the prevalence and, when formed, the persistence of Te⋯S secondary interactions operating in the crystal structures of tellurium 1,1-dithiolates that is one of two major motivations for the present survey of their crystallographically determined structures.

In addition to comments on structural aspects of tellurium compounds in the aforementioned reviews focussing on 1,1-dithiolate ligands [20], [21], [22], [23], more generally, the structural chemistry of tellurium has been reviewed periodically over the years by Abel et al. [40], Sudha and Singh [41], with the latest comprehensive survey, appearing in 1994, by Haiduc et al. [42].

The complementary focus of this survey of tellurium 1,1-dithiolate structures is a systematic investigation of the coordination environments in these molecules which may be influenced by two lone pairs of electrons in the tellurium(II) structures or one lone pair in the case of tellurium(IV) species. The pivotal role of stereochemically active lone pairs of electrons in rationalising geometries is readily appreciated by the wide applicability of the Valence Shell Electron Pair Repulsion (VSEPR) model for organic molecules [43], [44]. Stereochemically active lone pairs are also well known to influence coordination geometries in main group element compounds but in certain examples containing the heavier atoms, it is well known that the lone pair can be stereochemically inert [45], [46], [47]. This comes about as often greater coordination numbers are found in compounds of the heavier elements, meaning a diminishing contribution of the s-orbital to the overall bonding. An additional consequence of crowded coordination geometries is that it can sometimes be difficult to definitely detect the influence of a putative lone pair of electrons upon the molecular structure. A useful concept relating to the detection of lone pairs in high coordinate molecules involves considering the topological distribution of donor atoms about the central atom [48]. Here, a holodirected arrangement shows the ligand donor atoms to be distributed uniformly on the surface of sphere about the central donor which contrasts a hemidirected distribution whereby an obvious gap is apparent on the sphere that is ascribed to the presence of a lone pair of electrons [48]. Systematic studies of the heavier main group element compounds examining the influence of the lone pair of electrons are probably most developed for lead(II) compounds [49], [50], [51] with less attention been directed towards antimony(III) [35], [52], [53], [54] and bismuth [55], [56]. The role of lone pairs of electrons obviously has attracted considerable attention in tellurium structures [20], [21], [22], [23], [40], [41], [42] with the classic example of “stereochemical inertness” for tellurium(IV) compounds found in the [TeCl6]2− salts [57], [58].

With varying oxidation states, chemical compositions, and the putative influence of stereochemically active lone pairs, it is no surprise that a wide variety of coordination geometries are possible in the structures described herein. Table 1 summarises the more frequently encountered coordination geometries, and their designations. Coordination geometries are analysed in terms of formal covalent bonds along with the secondary Te⋯X interactions, whenever present. The criterion used to determine the “significance” of a Te⋯X interaction is simply based on the sum of the van der Waals radii, as tabulated by Bondi [59], e.g. 2.06A for tellurium, 1.80A for sulphur, etc.

In this survey, the structural chemistry of the tellurium(II) 1,1-dithiolates are described first followed by those of tellurium(IV). Within each division, binary compounds are discussed first, followed by ternary derivatives, usually containing one or more halide (pseudo-halide) donors. Finally, organotellurium compounds are described in order of increasing number of tellurium-bound organic substituents. All structural data were extracted from the Cambridge Crystallographic Data Centre [60]. Particularly relevant to the present survey are the 1,1-dithiolate ligands shown in Fig. 1, namely (I) N,N′-dialkyl(aryl)dithiocarbamate; (II) O-alkly(aryl)dithiocarbonate (xanthate); (III) O,O′-dialkyl(aryl)dithiophosphate; and (IV) dialkyl(aryl)dithiophosphinate, as all of these form compounds with tellurium(II)/(IV) that have been crystallographically determined. Within each of the specified categories, the structures are described in order of those containing (I), the most numerous, (II), (III) and finally, (IV), the least represented. When applicable, mixed 1,1-dithiolate ligand structures are discussed at the conclusion of each category. All crystallographic illustrations are original and were drawn with the aid of DIAMOND programme [61] using arbitrary spheres; hydrogen atoms are not illustrated to aid clarity.

Section snippets

Tellurium(II) compounds

Tellurium(II) 1,1-dithiolates are less numerous that their tellurium(IV) counterparts but, arguably display a greater diversity of coordination geometries and more varied supramolecular association patterns. An obvious explanation for the greater disparity in their coordination environments is explained in terms of the presence of two lone pairs of electrons around the tellurium(II) centre rather than one pair as for the tellurium(IV) structures.

Tellurium(IV) compounds

Tellurium(IV) is a reducing centre and 1,1-dithiolate ligands can be readily oxidised, e.g. S2CNEt2 to disulfiram, Et2NC(double bondS)SSC(double bondS)NEt2, S2COEt to dixanthogen, EtOC(double bondS)SSC(double bondS)COEt, and S2P(OEt)2 to (EtO)2P(double bondS)SSP(double bondS)(OEt)2, etc. [19]. Under these circumstances, the only binary 1,1-dithiolate compounds to have been characterised with tellurium(IV) are those containing dithiocarbamate ligands which are renowned for their ability to stabilise high oxidation states. Mixed ligand compounds, for example

Summary and conclusions

The foregoing description of the structural chemistry of crystallographically characterised tellurium 1,1-dithiolate compounds has focussed upon coordination geometries and supramolecular aggregation patterns. In terms of the former, significant influence exerted by lone pairs of electrons is evident. In the tellurium(II) species, the presence of two lone pairs of electrons is indicated in all coordination geometries. By contrast, often the lone pair of electrons in the tellurium(IV) structures

Acknowledgements

We thank CNPq, FAPESP and CAPES for financial support.

References (174)

  • O.H.J. Szolar

    Anal. Chim. Acta

    (2007)
  • H. Li et al.

    J. Inorg. Biochem.

    (2007)
  • D. Fan et al.

    Coord. Chem. Rev.

    (2007)
  • I. Haiduc et al.

    Polyhedron

    (1995)
  • N.W. Alcock

    Adv. Inorg. Chem. Radiochem.

    (1972)
  • E.W. Abel et al.

    Prog. Inorg. Chem.

    (1984)
  • N. Sudha et al.

    Coord. Chem. Rev.

    (1994)
  • R.J. Gillespie

    Coord. Chem. Rev.

    (2008)
  • R.L. Davidovich et al.

    Coord. Chem. Rev.

    (2009)
  • S.S. Dos Santos et al.

    J. Organomet. Chem.

    (2007)
  • P.C. Srivastava et al.

    Polyhedron

    (2008)
  • B.F. Hoskins et al.

    Inorg. Chim. Acta

    (1985)
  • J. Novosad et al.

    Polyhedron

    (1999)
  • B.F. Hoskins et al.

    Inorg. Chim. Acta

    (1985)
  • N.A.G. Bandeira et al.

    Inorg. Chim. Acta

    (2003)
  • R.K. Kumar et al.

    Polyhedron

    (1996)
  • R.K. Kumar et al.

    Polyhedron

    (1993)
  • R.W. Gable et al.

    Inorg. Chim. Acta

    (1983)
  • A.A. West et al.

    J. Organomet. Chem.

    (1988)
  • S. Cecconi et al.

    Curr. Pharm. Des.

    (2007)
  • C. Rafin et al.

    J. Agric. Food Chem.

    (2000)
  • B. Cvek et al.

    Curr. Pharm. Des.

    (2007)
  • R. Malcolm et al.

    Exp. Opin. Drug Saf.

    (2008)
  • Z.E. Sauna et al.

    Mol. Biosyst.

    (2005)
  • V. Milacic et al.

    Histol. Histopathol.

    (2008)
  • L. Ronconi et al.

    J. Med. Chem.

    (2006)
  • D. de Vos et al.

    Bioinorg. Chem. Appl.

    (2004)
  • B. Quiclet-Sire et al.

    Chem. Eur. J.

    (2006)
  • R.S. Grainger et al.

    Heteroatom Chem.

    (2007)
  • O.J. Plante et al.

    J. Am. Chem. Soc.

    (2001)
  • M.S. Vickers et al.

    J. Mater. Chem.

    (2006)
  • Y.W. Koh et al.

    Chem. Mater.

    (2003)
  • J.R. Castro et al.

    J. Mater. Chem.

    (2008)
  • N. Alam et al.

    Chem. Mater.

    (2008)
  • I. Haiduc
  • P.J. Heard

    Prog. Inorg. Chem.

    (2005)
  • G. Hogarth

    Prog. Inorg. Chem.

    (2005)
  • E.R.T. Tiekink et al.

    Prog. Inorg. Chem.

    (2005)
  • J. Cookson et al.

    Dalton Trans.

    (2007)
  • E.R. Knight et al.

    Dalton Trans.

    (2009)
  • E. Santacruz-Juárez et al.

    Inorg. Chem.

    (2008)
  • J. Cruz-Huerta et al.

    Inorg. Chem.

    (2008)
  • C.S. Lai et al.

    CrystEngComm

    (2002)
  • C.S. Lai et al.

    CrystEngComm

    (2004)
  • C.S. Lai et al.

    CrystEngComm

    (2004)
  • D. Chen et al.

    CrystEngComm

    (2006)
  • R.E. Benson et al.

    CrystEngComm

    (2007)
  • R.A. Howie et al.

    CrystEngComm

    (2008)
  • E.R.T. Tiekink

    CrystEngComm

    (2003)
  • Y. Liu et al.

    CrystEngComm

    (2005)
  • Cited by (48)

    • Main group metal coordination chemistry

      2023, Comprehensive Inorganic Chemistry III, Third Edition
    • Chalcogen bonding in coordination chemistry

      2022, Coordination Chemistry Reviews
      Citation Excerpt :

      In the last few decades, organotellurium compounds and their metal complexes have attracted considerable attention in view of their structural features, reactivity and unusual properties, as well as applications in functional devices, solar panels, catalysis and medicine [182–187]. In comparison to the lighter chalcogens, the Pauling electronegativity of tellurium is significantly lower [O (3.44), S (2.58), Se (2.55), Te (2.10)], and thus Te displays a stronger ChB donor ability towards nucleophiles in intra- or intermolecular interactions in organotellurium compounds or their metal complexes [188–191]. In fact, the noncovalent interactions involving tellurium that achieve the strength of chalcogen bonds can be important for improving functional properties of metal complex comprising materials, and in particular in crystal engineering namely supramolecular assembly/aggregation of tectons.

    View all citing articles on Scopus
    View full text