X-RAY INVESTIGATION OF INTERNAL COMPLEXES OF 8-MERCAPTO-QUINOLINE AND ITS DERIVATES WITH TRANSITION METALS.

Lucija Pech¹ , Jurii Bankovsky¹ , Vitaly Belsky², Andrejs Kemme³, Elga Silina¹, Janis Ashaks¹, Aivars Sturis¹.

¹Institut of Inorganic Chemistry , Latvian Academy of Sciences, 34 Miera Street, Salaspils, LV-2169;
²Karpov Institute of Physical Chemistry Moscow, Russia;
³Latvian Institute of Organic Synthesis, 21 Aizkraukles Street, Riga, LV-1006, Latvia.
E-mail: director@iic.iph.sal.lv

Keywords: inorganic coordination compounds, transition metals, 8-mercapto-quinoline and its derivatives

The aim of the present study is to juxtapose the molecular and crystal structure of 23 ( I-XXIII ) internal complexes of 8-mercaptoquinoline and its derivatives and to establish the regularities of their spatial structure depending on the nature of complexing metal and that of substituents and their position in the quinoline ring [1]. The following structures are discussed: palladium, platinum, nickel and copper 8-mercaptoquinolinates ( compounds I, IV, VII and X, respectively), palladium and platinum 5-phenylthio-8-mercaptoquinolinates (II, V), palladium and nickel 5-trimethylsilylmethylthio -8-mercaptoquinolinates ( III and IX ), platinum 7-methyl-8-mercaptoquinolinate ( VI ), nickel 5-propylthio-8-mercaptoquinolinate ( VIII ), copper 5- and 7-methylthio-8-mercaptoquinolinates ( XI and XII, respectively) possessing a planar structure with the complexing metal atom in the center of symmetry of complexes. The particular significance of contacts between the metal atom and ligand atoms of the neighbouring molecules in the general structure of crystals I-XII has been demonstrated. The planar complexes bound mainly by the mentioned interaction form stacks along one, mostly the shortest, crystallographic axis in the structures. Some parameters of the crystal surrounding of the metal atom in the mentioned compounds are:

					Bond length A											 coodination polyhedron 

			M			 M-S			 M-N			 M...X 

I		       Pd			 2.282			 2.01			 Pd...C5 3.86				 square-planar 

II		       Pd			 2.304(2) 			2.039(1)  				  "	

III		       Pd			 2.294(1)			 2.039(3) 				     " 

VI		       Pt			 2.265			 2.05			 Pt...C5 3.94  		  "

V 		       Pt			 2.302(3)			 2.023(3)    										"

VI		       Pt			 2.302(1)			 2.029(5)											 " 

VII		       Ni 			 2.40			 2.06			 Ni...S1 2.60					 octahedron 

VIII                Ni			 2.195(2)			 1.987(7) 			 Ni... S2 3.61					 square-planar 

IX                  Ni    			 2.179(2)			 1.937(5)											 " 

X                   Cu 			 2.31			 2.08			 Cu...S1 3.07					 lengthened octahedron 

XI		      Cu 			 2.278(2)			 2.040(7)			 Cu...S2 3.30						 " 

XII		      Cu 			 2.264(2)			 2.032(5)			 Cu ...C5 3.41						 " 

The presented data give evidence how the real coordination of the M atom as well as the length of M-N and M-S1 bonds is changed depending on the strength of the M...X contacts. The occurrence of the strong interaction Ni...S1 in the complex VII leads to the almost regular octahedral surrounding of the nickel atom and to the essential weakening of the Ni-N and Ni-S1 bonds in comparison with the nickel complex VIII. In the isostructural complex of copper X the contacts Cu...S1 due to the Jan Teller effect are longer. According to the weakening of the Cu...X interaction in the series of complexes of copper X, XI, XII the certain minor, nevertheless regular strengthening of the Cu-N and Cu-S1 bonds can be observed.The strongest intermolecular contacts M...X cause the irregularity of the planar structure of the metal-containing cycles.The molecules VII, X and XII possessing the step-shaped form. In the complexes I, IV, VIII in which the metal-ligand contacts depend on the weak electrostatic interactions the metal and sulfur atoms lie in the planes of quinoline nucles.

Nonplanar palladium, platinum, nickel and cobalt 2-methyl-8-mercaptoquinolinates ( compounds XIII, XIV, XVII and XXI, respectively ), platinum and copper 2,7-dimethyl-8-mercaptoquinolinates ( XV and XX ), platinum, nickel and cobalt 2-isoprophyl-8-mercaptoquinolinates ( XVI, XVIII and XXII ), nickel and cobalt 2-phenyl-8-mercaptoquinolinates ( XIX and XXIII) possessing the more or less distorted tetrahedral structure. Such a distortion is caused by sterical hindrance of substituent in position "2". On the basis of date obtained by X-ray diffraction analysis the reasons of changes in strength of the bonds "metal-sulfur" and "metal-nitrogen" have been analysed; the intermolecular contacts in crystals have been investigated.

It was established that the greatest changes of the structure of the central coordination angle and the geometry of the complex, on the whole, are observed upon transition from complexes of 8-mercaptoquinoline to the complexes of its 2-substitutes with introduction of substituents of other positions of the quinoline ring, these changes are negligible.

From the degree of distortion of the square -planar structure of 8-mercaptoquinoline on transition to the tetrahedral structure due to the sterical hindrance of the subtituent in position "2" the relative strength of the chemical bond in relation of nature of metal and ligand atoms have been evaluated.

The ascertainment of such effect allows to explain the changes in physicochemical properties of 2-substituted 8-mercaptoquinolinates (hypsochromic shift of absorption maxima, decrease of the amount of ligands connected to the central atom, decrease of stability, increase of solubility in organic solvents ) in comparison with 8-mercaptoquinolinates.

1. A.P.Sturis, Yu.A.Bankovsky, L.J.Pech. Izv. Akad. Nauk Latv. SSR, Ser. Khim. 3 (1990) 259-277.