The crystal structure of diethyl(salicylaldehydato)thallium(III)
The complex, Et2(C7H5O2)Tl, which gives an alkaline aqueous solution and is monomeric in chloroform, has been shown by three-dimensional X-ray crystal structure analysis to be a chain polymer in the solid. There are four formula units in a triclinic unit cell having a= 8·00, b= 20·71, c= 7·71 Å, α= 100·7, β= 101·6, γ= 88·4°, and space group C. The thallium, oxygen, and carbon atoms were unequivocally located by Patterson and Fourier methods; hydrogen atoms were neglected. Refinement by least-squares, allowing for anisotropic vibration of the thallium atom and individual isotropic vibration parameters for the other atoms, gave an R-value of 0·095.
The striking feature of the structure is that infinite chains Tl[graphic omited]Tl[graphic omited]Tl run through the crystal in the direction of the a-axis. Each chain consists of centrosymmetrical four-membered rings which are formed alternately from phenolic, O(1), and aldehydic, O(2), oxygen atoms. These rings are nearly coplanar, the angle between their normals being 6°, and are closely parallel to (001), a marked cleavage plane. The chains are separated by half a unit cell along b and one unit cell along c.
Each thallium atom is 6-co-ordinated, by two ethyl groups with Tl–C = 2·17 ± 0·04 Å and C–Tl–C = 172·3 ± 1°, by two oxygen atoms in a chelating salicylaldehydato group with Tl–O(1)= 2·46 ± 0·02 Å and Tl–O(2)= 2·61 ± 0·02 Å and two more oxygen atoms which are part of chelate rings on neighbouring thallium atoms at Tl–O(1)′= 2·65 ± 0·02 Å and Tl–O(2)′= 3·15 ± 0·02 Å, so the polymer-forming Tl–O bonds are longer than those in the chelate ring. The C–Tl–O bond angles are all close to 90°; in the chelate ring O(1)–Tl–O(2)= 71·2 ± 0·7°, in the 4-membered Tl–O–O–Tl rings O(1)–Tl–O(2)′= 81·0 ± 0·7°, O(2)–Tl–O(2)′= 86·1 ± 0·7°, and the remaining angle, O(1)′–Tl–O(2)′= 122·0 ± 0·7°. The bond lengths in the ligand molecules are all normal. The salicylaldehydato group is planar, and the thallium atom is 0·85 Å from this plane.