Crystal structure of a new polymeric thallium-lasalocid complex: lasalocide anion-thallium(I) containing aryl-Tl interactions

The title complex, [Tl(C 34 H 53 O 8 )] n , forms a pseudo individual monomer complex, in which the anionic oxygen of carboxylate group serves to neutralise the charge of Tl + , the other five O centres of the first lasalocid anionic ligand (Lasa 1) and in which this ligand is pentadentate O-ligand and bonded to a second Tl centre by using phenyl-metal coordination. A second lasalocid ligand (Lasa 2) is also pentadentate O-ligand and bridges the first Tl centre within the polymer. The monomeric unit is stabilized by strong intramolecular aryl-Tl type-metal half sandwich bonding interactions.


Introduction
Lasalocid A salt of sodium is one of the most commonly used veterinary antibiotics, where it has found wide spread application as an anticoccidial and to improve feed efficiency.The mechanism of action of lasalocid is clearly attributed to its ionophoric properties, because it has been reported to determine the influx of Na + in the cell of Gram positive and anaerobic bacteria, causing swelling, vacuolization, and death.At the origin of these processes, there is the property of forming lipophilic metal complexes, which can penetrate membranes and disrupt cation equilibria. 1,2he molecular basis of this action are still debated; more specifically which of the oxygen atoms are directly involved in cation coordination.To date, this problem has been the object of many investigations almost invariably taking advantage of the concerted use of several experimental and computational techniques, which demonstrate both the relevance of the problem and its intrinsic difficulty. 3he identity of the various complexes formed according to the nature of the cation, to the solvent, and to the solution composition has been initially faced with optical spectroscopy and circular dichroism (CD), possibly using lanthanides as probes. 4X-ray diffraction data became available for several cations, among others Na + , 5 and Ba 2+ . 6Often, it has been observed that aggregates of different stoichiometry can take place, leading to the formation of sandwiches, where the cation occupies a cavity between two ligand molecules. 3Molecular dynamic calculations have been reported both in vacuo, 7 and in solvent. 8Finally, there has recently appeared a series of papers on polyoxaalkyllasalocid esters/cation complexes making use of multinuclear NMR, IR, ESI-MS, and semiempirical methods. 9It has been proposed that antibacterial and fungicidal activity and also antitumor and anti-HIV-integrase inhibition of antibiotics lie in their ability to chelate the essential metals, which the micro-organisms need in their metabolism. 9

Results and Discussion
We report the synthesis and structure of the first compound of a series of Lasalocid-thallium(I) complexes that is readily prepared as its pure stochioisomer ligand/metal (1/1).This new thallium (I) complex, deriving from lasalocid / thallium coordination, is obtained through two simple and economical synthetic methods (Scheme 1).
] So it is difficult to give precise details about the site of coordination on the basis of NMR data (Tables 1 and 2).

Crystallographic study
The crystallographically complementary coordinating aryl group is located on a second lasalocid (Lasa 2).These two lasalocid ligands (Lasa 1 and Lasa 2) are not tied together by a threedimensional hydrogen-bonding network as it was observed previously by Akkurt et al. in the case of [Sr(Lasa) 2 (H 2 O)] as it is reported. 12These monomeric units are not stacked by any Van der Waals forces between the coordination spheres (Figures 1 and 2).To have a clear idea about the coordinative aspect of the lasalocid ligands leading to a polymeric aspect of this complex, the view for the complex [Tl(Lasa)] n has been added here as shown in Figure 4.This complex between thallium(I) and antibiotic lasalocid ligand is a polymer.It is based on dimeric, non centrosymmetric Tl 2 (Lasalocid) 2 units without 2 -bridging carboxylic groups resulting in Tl•••Tl separations of 7.65-7.70Å.These dimeric units are further linked to form infinite coordination polymers.In bis [(lasalocid anion)-thallium(I)] (1) are adjacent units are held together by secondary Tl-(phenyl) p-interactions resulting in a crystal organization which can be described as half sandwich, infinite two-dimensional polymers.Another characteristic structural motif is the tendency of the thallium ion to only use less than one hemisphere to coordinate ligands.This half-nakedness is due to the stereochemically active inert pair (6s 2 ), which thus plays a prominent role in controlling the structures of these compounds. 17The Tl + cations are in approximate pyramidal geometries, with five oxygen donor atoms in the basal plane and the stereoactive lone pair occupying the apex position of the pyramid.There are, on the naked side of the metal ions, relatively large spaces in nonpolar environments provided by neighboring phenyl groups.The distances between the planes of the phenyl rings and the Tl + cation are in the range 3.43-3.50Å, indicating that Tl + -phenyl 6 -interactions are important in the crystal organization.

Conclusions
In conclusion, we describe here what is to our knowledge the first solid-state structure obtained with a thallium-lasalocid complex.The tetra-butyl ammonium salt of lasalocid is able to form a stable 1:1 (ligand:metal) complex with monovalent cations such as thallium(I).The structure of this complex is completely different with the respective complexes with other monovalent cations and divalent cations (Mg 2+ and Ca 2+ ). 15n contrast to Sr-lasalocid complex, the study of in vitro biological activity of the Tl-Lasalocid on fungus F. oxysporum, at Oujda, shows that this compound is not biologically active.This contrast in this biological antifungal screening for the same ligand containing different metals is very important for future agricultural applications and deserves to be extended to a wide series of transition metals [Ru(II), Co(II), Fe(II)].

Experimental Section Preparation of complex (2)
Method (A).A solution of lasalocid free acid (1 mmole, prepared in 20 mL of CHCl 3 was stirred with 0.1 M aqueous Tl 2 CO 3 (0.7 mmole, prepared in 30 mL of H 2 O).The mixture was stirred at 20 °C for 2 hours.The organic layer was then dried over anhydrous Na 2 SO 4 , filtered and evaporated.The solid residue was dissolved in MeOH and the solvent was left to evaporate at 20 °C for 1 week in the dark.White crystals obtained proved suitable for X-ray analysis (83% Yield).

Method (B).
A solution of lasalocid free acid (1 mmole, prepared in 20 mL of CHCl 3 was stirred with 0.1 M aqueous TlOH (1.2 mmole, prepared in 30 mL of H 2 O).The mixture was stirred at 20 °C for 3 hours.The organic layer was then dried over anhydrous Na 2 SO 4 , filtered and evaporated.The solid residue was dissolved in MeOH and the solvent was left to evaporate at 20 °C for 1 week in the dark.White crystals obtained proved suitable for X-ray analysis (85% Yield).The complex (2) is characterised by 1 H and 13 C NMR by using Bruker AC 400 MHz spectrometer.The purity of product (2) is excellent (99.5%).
Crystal structure analysis.The crystal structure of the title compound, Tl(C 34 H 53 O 8 ), has been determined at room temperature.Diffraction data were collected using a Bruker SMART APEXII CCD diffractometer system, using graphite-monochromated MoKα radiation.The crystallographic details are given in Table 1.The structure was solved by direct methods by using SIR-97 program and refined by least-squares on Fobs 2 and by using SHELXL-97 programs.O1, O4 and O6 H atoms were located in a difference Fourier map and refined freely.All other H atoms were located in calculated positions and treated as riding on their parent atoms, with C-H = 0.96 (CH 3 ), 0.97 (CH 2 ) or 0.98 Å (CH), and with U iso (H) = 1.5U eq (CH 3 ) or 1.2U eq (CH 2 , CH).A displacement ellipsoid plot with the atomic numbering scheme of the title compound is shown in Figure 2; with selected bond lengths, bond and torsion angles angles, and hydrogen-bonding geometry in Tables 2 and 3 13 The crystal polymeric structure is stabilized by the metal-aryl Tl(i)---Aryl (Lasa i+1) and Tl(i+1)---Aryl (Lasa i+2) [ ring-metal interactions with π-Ph ≤ 4 Å -symmetry code: 1-x, 1/2+y, 1/2-z ] type-half sandwich bonding interactions (Table 2).The molecular and crystal structures are stabilized by the O-H O and C-H O typehydrogen bonding interactions (Table 5, Figure 2).(Δρ) min = -0.54eÅ -3 Measurements: Bruker SMART APEX-II CCD diffractometer 14 Structure determination: SIR97 15 Refinement: full matrix least-squares SHELXL-97 16 Note: CCDC 682527 contains the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic

Figure 1 .
Figure 1.An ORTEP view of the title compound, with the atom-numbering scheme.Displacement ellipsoids are drawn at the 50% probability level.

Figure 2 .
Figure 2. A view of the hydrogen bonding of the title compound.H atoms not involved in hydrogen bonding have been omitted for clarity.

Figures 3 .
Figures 3. A view of the aryl-Thallium and Thallium-Oxygen bonding of the title compound.This figure was obtained by displaying packing and short contacts.
, respectively.The title complex, [Tl(C 34 H 53 O 8 )], crystallizes with five-coordinated Tl atom three dimensionally interconnected into a polymeric structure.The thallium atom shows a distorted trigonalpyramidal coordination geometry formed by five O atoms.The mean Tl-O bond lengths 2.9352(3) Å.The geometric parameters of the present structure agree with those previously studied at room temperature but with significantly improved precision.Within the ligands, other geometric parameters (C-O and C-C distances, and O-C-O and O-C-C angles) all lie in the expected ranges.

Table 3 .
Crystal and experimental data.