Crystal structures of Pt(II) and Pd(II) complexes with the free radical 4-aminoTEMPO

Pt(II) and Pd(II) compounds containing the free radical 4-aminoTEMPO (4amTEMPO) were synthesized and characterised by X-ray diffraction methods. The disubstituted complexes cis- and trans-Pt(4amTEMPO)2I2 were studied. The trans isomer was prepared from the isomerisation of the cis analogue. The two Pd(II) compounds trans-Pd(4amTEMPO)2X2 (X = Cl and I) were also characterised by crystallographic methods. A mixed-ligand complex cis-Pt(DMSO)(4amTEMPO)Cl2 was synthesized from the isomerisation of the trans isomer in hot water. Its crystal structure was also determined. In all the complexes, the 4amTEMPO ligand is bonded to the metal through the –NH2 group, since the nitroxide O atom is not a good donor atom for the soft Pt(II) and Pd(II) metals. The conformation of the 4-aminoTEMPO ligand was compared to those of the few reported structures in the literature.