SYNTHESES AND COORDINATION PROPERTIES OF DERIVATIVES OF PIPERAZINE THIOMORPHOLINE AND MORPHOLINE

Abstract

A series of ligands containing two N-benzoylpiperazine units linked by alkyl bridges of two-, three-, four- and six-carbon atoms are synthesised. 1,2- bis(N-benzoylpiperazino)ethane acts in a bidentate fashion in its zinc(II) and cobalt(II) complexes as confirmed by X-ray crystallography. 1,3-Bis(N- benzoylpiperazino)propane chelates with zinc(II) chloride in a similar bidentate manner. Acid hydrolysis of 1,3-bis(N-benzoylpiperazino)propane affords 1,3- bis(piperazino)propane This ligand forms complexes with nickel(II), copper(II) and palladium(II) ions. In its palladium(II) perchlorate complex, the ligand behaves as a tetradentate chelating agent using its four nitrogen atoms as the donors. The coordination structure is a distorted square plane. 1H NMR spectra show that at low temperatures all the eight protons are magnetically different. 1,3-Bis(N-methylpiperazino)propane was prepared for comparison, whose palladium(II) complex possesses a distorted square planar coordination structure too. Three thiomorpholine derivatives, 1,3-bis(thiomorpholino)propane, 2,6- bis(thiomorpholinomethyl)pyridine and 1, 1, 1-tris(thiomorpholinomethyl)ethane were also synthisised. 1,3-Bis(thiomorpholino)propane can act in two manners: bidentate and tetradentate. In its zinc(II) chloride complex, the ligand coordinates to the central atom using its two nitrogen atoms, together with the two chlorine atoms, to form a tetrahedral coordination structure. In its palladium(II) perchlorate and rhodium(III) chloride complexes, the ligand acts in a tetradentate fashion using all of four hetero atoms. It appears that its coordinating ability depends on the nature of the metal atoms. 2,6-Bis(thiomorpholinomethyl)pyridine is potentially a pentadentate ligand. Its complexes with nitrates of palladium(II), nickel(II) and copper(II) were prepared and characterised. In all the three complexes, the ligand functions as a tridentate ligand utilising its three nitrogen atoms while the two sulphur ones remain free. The Pd complex possesses a distorted square planar coordination geometry with one of the two nitrato groups coordinating as a unidentate ligand and the another ionic. The Pd-N(pyridine) bond length is 1.857(4) Å, which is believed to be the shortest Pd-N separation ever observed. In the Cu complex, the copper atom is five-coordinated in a distorted square planar arrangement with the two nitrato groups acting as unidentate ligands and occupying the apex and one equatorial position. The Ni complex has a distorted octahedral coordination sphere; one nitrato group behaves in a chelating fashion and the other unidentate. 1, 1, 1-Tris(thiomorpholinomethyl)ethane forms an 1:1 complex with palladium( II) perchlorate using its two thiomorpholine units to give a square planar coordination structure. The third thiomorpholine ring is not involved in bonding. Ligand 1-morpholino-3-piperazinopropane contains both a morpholine ring and a piperazine ring. Crystal structure shows that in its palladium(II) complex, chloro(1-morpholino-3-piperazinopropane)palladium(II) hexafluoro- phosphate, the ligand coordinates to the Pd(II) atom using its three nitrogen atoms and the oxygen atom is not involved in bonding.