Síntese e caracterização de compostos binucleares de rutênio e ferro com o ligante bis(4-Piridilmetil)dissulfeto

Abstract

The mononuclear Na3[(CN)5FeBPMS].3H2O and [(NH3)5RuBPMS](PF6)2 complexes were obtained by the reaction of monocoordenative ions [(CN)5FeNH3]3- and [Ru(NH3)5OH2]2+ with the ligand bis(4-pyridilmethyl)dissulfide, BPMS. The complexes have been characterized by microanalyses, vibrational and eletronic spectroscopies and electrochemical techniques. Kinetic study data of the ligand substitution reaction have shown consistence with the assignment of dissociative mechanism. The activation parameters ΔH# = 99,78 kj mol-1 and ΔS# = 33,72 J mol-1K-1 have been calculated and fit in the isokinect curve correlation of a wide series of similar complexes with N-heterocyclic ligands. The rate constant kobs = 1,25 x 10-3 s-1 was found to be very close to that observed for pyridine derivatives complexes indicating that the pyridine ring coordinated to these metal centers are equally influenced concerning to their lability. The electrochemical studies of the mononuclear complexes were performed by using cycle voltammetry and differential pulse polarography techniques. The collected data have been consistent with the reversibility of the M(III)/M(II) redox processes. The plot of the potential values along with those related in the Iiterature for similar systems have pointed out the role of the "back-bonding" dπ-->pπ* on the stabilization of the reduced metal center, M(II), compared with oxidized. M(III), specie. The symmetric binuclear complexes [(NH3)5RuBPMSRu(NH3)5](PF6)4 and Na6[(CN)5FeBPMSFe(CN)5].3H2O were isolated and characterized by using spectroscopic and electrochemical techniques. The comproportionation constants values indicate weak electronic coupling between the metal centers following the behavior of Robin and Day class I compounds. This observation in both RuBPMSRu and FeBPMSFe systems reinforce the assignment of electron transfer mechanism in the DTDP binuclear complexes thought to be trough bond involving the sulfur d orbitals. In the particular bis(4-pyridilmethyl)disulfide system the sulfur d orbital participation would be inhibited by the presence of two CH2 groups by blocking the eletronic delocalization trom dπ M(II)-->pπ*(Py ring) "back-bonding" to M(III) trough the -SS-bridge.