Magnetic and Spectroscopic Studies on some New Bis- and Tris-complexes of Iron(II) with 3,5-Dimethy1- 1-(2`-pyridyl)pyrazole : Indication of 5T2 'Ai Equilibrium

Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Calcutta-700 009 The synthesis and physicochemical characterisation (including magnetic measure­ments over a temperature range and MOssbauer spectra) of a host of bis- and tris­iron(u) complexes with the title ligand, viz. 3,5-dimethy1-1-(2'-pyridyl)pyrazole (DPyPz) are reported. The tis-complexes Fe(DPyPz)2X2.nH2O (X =Cl, Br, NCS ; n = 0, 2) are clearly of high-spin type (µe f =5.00— 5.40 B.M. at 298 K) with temperature-independent magnetic moment values, whereas the bis-perchlorate, the tris-perchlorate and the tris-iodide species show intermediate magnetic moment values (µeff =2.56 and 2.28 B.M. respectively at 293 K) which have been rationalised in terms of 5T2→1A1 equilibrium. The diffuse reflectance spectra of all the iron(II) complexes are indicative of 5T2g→5 Eg transition in an octahedral environment. An approximate octahedral configuration around iron(II) nucleus has also been ascertained from the values of isomeric shift and quadrupole splitting of 57Fe Mossbauer spectrum of a representative complex. ir data point out the pyrazolyl and the pyridine nitrogens of the title ligand as the bonding sites when complexed with iron(II) ; the counterions (X) are mostly coordinated in the bis-species while the same retain their ionic character in the tris­complexes