Abstract
Abstract: Reactions of TlCl 3 with picolinic acid (Hpic), nicotinic acid (Hnic), isonicotinic acid (Hinic) and 3-hydroxy-picolinic acid (H3hpic) a¬ord the isolation of new chlorothallium(III) complexes. The compounds are characterized by IR, Raman and multinuclear NMR ( 1 H, 
Introduction
Complexes of pyridine carboxylic acids with \p", \d" and \f" metals have been studied in order to elucidate the coordination modes of these ligands. A survey of the reported molecular structure determinations for metal complexes reveals that the O,Nmonometallic biconnective (bidentate) (Scheme 1, structures I and II) is the most usual coordination pattern for the deprotonated form of the picolinic (Hpic) and 3-hydroxypicolinic (H3hpic) acids [1, 2, 3, 4] . Nicotinic (Hnic) and isonicotinic (Hinic) acids were found to coordinate: (i) as unidentate, neutral ligands only through the pyridyl nitrogen atom (Scheme 1, structures IIIa and IVa) [5, 6] , (ii ) as O,O-bimetallic biconnective (bridging) ligands (Scheme 1, structures IIIb and IVb) [7, 8] , and (iii ) as O,O; N -bimetallic triconnective (tridentate) groups (Scheme 1, structures IIIc and IVc) [9, 10] . The presence of the carboxylate group as substituent in position 2 of the pyridine ring usually leads to O,N -monometallic biconnective (chelate) coordination, while substitution in position 3 or 4 promotes the formation of supramolecular associations through bridging ligands.
The present work reports the reactions of TlCl 3 with Hpic, Hnic or Hinic in 1:2 molar ratio, and H3hpic 1:3 molar ratio, respectively, which a®ord the isolation of new chlorothallium(III) complexes. The compounds are characterized by IR, Raman and multinuclear NMR ( 1 H, 13 (4) are determinated by single-crystal X-ray di®raction.
Experimental
The starting materials were purchased from commercial sources: anhydrous TlCl 3 (Aldrich), picolinic acid (Merck), 3-hydroxypicolinic acid (Fluka), nicotinic acid (Merck), isonicotinic acid (Merck). All other chemicals were AR grade and used without further puri¯cation. Elemental analysis (C, H, N) was performed using a Fisons 1108 and Perkin Elmer analyzers. Melting points were determined with a BÄ uchi apparatus and molar conductivities with a Crison CM 2202 conductometer. IR spectra were recorded on a Bruker IFS-66 spectrometer using KBr pellets (4000-500 cm ¡1 ) and nujol mulls (500-100 cm ¡1 ). Raman spectra (3000-100 cm ¡1 ) were recorded using a FRA-106 module coupled with a Bruker IFS-66 spectrometer. The 1 H, 13 C and 205 Tl NMR spectra were recorded on a Bruker AMX-300 spectrometer kristinlang@example.com, 75.4 and 173.5 MHz, respectively, using DMSO-d 6 solutions, at room temperature. Chemical shifts are reported in ppm and were referenced to TMS using the solvent signal for 1 H and 13 C spectra ( 1 H: 2.50 ppm, 13 C: 39.50 ppm) and an aqueous TlClO 4 solution after extrapolation to in¯nite dilution for the 205 Tl spectra. (Table 1) A solution of TlCl 3 in acetonitrile (5 mL) was added drop-wise with magnetic stirring to a solution of corresponding pyridine carboxylic acid ( given in Table 2 and 3 along with other experimental parameters. The intensities were corrected for Lorentz polarization factors. The structures were solved using the Patterson method for heavy atoms and re¯ned by full matrix least-squares methods for the location of the remaining non-hydrogen atoms (SHELX 97 [12] ). All of the non-hydrogen atoms were treated anisotropically. Hydrogen atoms on carbons were included in the model at geometrically calculated positions. The acidic hydrogens, i.e. the H(1) attached to N(1) atom in 2 was calculated as bonded to N(1) although its real position is probably somewhere between N(1) and O(4); and H(1), H(5), H(9) and H(10) on O(3), O (6) , N(3) and O(9), respectively, in 4, were located in the di®erence map and re¯ned using a rigid model. For compound 1, the acidic hydrogens could not be localized from the di®erence map and due to the disorder in one oxygen of a carboxylate group [0.30, 0.35 and 0.35 occupancies for O(4a), O(4b) and O(4c), respectively] neither were calculated. The drawings were made using the ORTEP [13] and DIAMOND [14] programs.
Preparation of the thallium(III) complexes
Selected distances and bond angles are given in Tables 4 and 5 , and the molecules are displayed in the ORTEP diagrams in Figures 1, 2, 4 and 5. Additional material is available from the Cambridge Crystallographic Data Center comprising the¯nal atomic coordinates for all atoms, thermal parameters, and a complete listing of bond distances and angles.
Results and discussion
The reactions between TlCl 3 and picolinic acid (Hpic), nicotinic acid (Hnic) and isonicotinic acid (Hinic) (1:2 molar ratio) and with 3-hydroxypicolinic acid (H3hpic) (1:3 molar ratio) are carried out in a acetonitrile/ethanol or CH 3 CN/water solution, according to equations (1) { (3):
3
4
In all cases, the resulting white precipitate is¯ltered o®, washed with ethanol, and dried in vacuum over CaCl 2 /KOH. The results of the microanalyses (C, H, N) are consistent with the formulation of the isolated products as 1:1 adducts, i.e. and the Raman (500-100 cm ¡1 ) spectra of all four complexes [18, 19, 20] .
NMR spectra
The NMR spectra were recorded in DMSO-d 6 due to the low solubility of the complexes in the other organic solvents. The assignments of the 1 H and 13 C resonances are made by comparison with the spectra of the corresponding organic acids [4, 21] , using the numbering scheme given below:
For compounds 1, 2 and 4, one would expect two sets of resonances corresponding to the deprotonated and the neutral ligands from the molecular unit. However, a common feature of the 1 H and 13 (ii ) most of the thallium-oxygen bond distances are in the range 2.278(4)-2.474 (9) The crystal of 1 consists of discrete molecules separated by normal van der Waals distances. Two independent, very similar molecules 1a and 1b are present in the asymmetric unit of 1 and, in the subsequent discussion, we will refer only to molecule 1b since molecule 1a shows some disorder in one of the carboxylate groups (see experimental). Selected interatomic distances and angles are listed in Table 4 . Figure 1 shows the ORTEP-like view of the molecular structure of 1b with the atom numbering scheme. In order for compound 1 to be neutral, one of the organic ligands in the molecular unit should contain a COOH group, but the corresponding hydrogen could not be located. The possibility of having two deprotonated ligands on one molecule and two neutral ligands on the other one can probably be ruled out since the compound behaves as a non-electrolyte in DMF. The two organic ligands from the molecular unit of 1b act as O,N -monometallic biconnective moieties through one oxygen of the carboxylate group and the pyridyl nitrogen atom, resulting in¯ve-membered TlONC 2 rings. Although only one oxygen atom of a carboxylate group is involved in coordination to the metal center for molecule 1b, there are no signi¯cant di®erences in the C-O bond lengths (c.f. 1.241(11)-1.265(12) º A vs. 1.214(2) and 1.278(2) in the free acid [33] ).
The resulting TlCl 2 N 2 O 2 core is a distorted octahedron with cis-Tl-Cl bonds [Cl(3)-Tl(2)-Cl(4) 108.79 (7) o ] and oxygen atoms trans to the chlorine atoms [Cl (3) The presence of the carboxylate group as a substituent in position 3 of the heterocyclic moiety in the nicotinic acid precludes the O,N -monometallic biconnective coordination. In the molecular units of 2, the organic ligands are coordinated to the metal center through both oxygen atoms of the carboxylate group (Table 4) o , (') = 1-x, -y, 1-z] hydrogen bridges, forming a double chain as shown in Figure 3 .
The reaction of TlCl 3 with Hinic and H3hpic a®ords the chlorothallium(III) derivatives 3 and 4 instead of the dichlorothallium(III) complexes. Selected interatomic distances and angles for these compounds are listed in Table 5 . Despite the monodentate or strongly asymmetric bidentate nature of a carboxylate group, the carbon-oxygen bond lengths are of the same magnitude within experimental error [range 1.238(7) -1.284(7) º A], probably due to the intramolecular hydrogen bonding established with the hydroxy substituents on the aromatic rings (Table 6 ). Moreover, in the crystal, the molecular units of 4 are associated through intermolecular N(3)-H(9)¢ ¢ ¢O(4') bridges into discrete dimers (Fig. 6 ).
Supplementary material
Crystallographic data for the structural analysis of compounds [1] [2] [3] [4] 

{'paper_id': '96023938', 'title': 'New thallium(III) chloride complexes with pyridine carboxylic acids: from molecular compounds to supramolecular associations', 's2_url': 'https://api.semanticscholar.org/CorpusID:96023938', 'source': 'S2ORC'}