Spin Equilibria in Octahedral Iron(II) Complexes with Some Hexadentate Ligands of the Tetrakis(2-pyridylmethyl)ethylenediamine Type and a Spectral Correlation With Their Cobalt(III) and Nickel(II) Analogs.

Abstract

N,N,N',N'-Tetrakis(2-pyridylmethyl)propylenediamine (tppn), N,N,N',N'-tetrakis(2-pyridylmethyl)trimethylenediamine (tptn), N,N,N',N'-tetrakis(2-pyridylmethyl)-trans-1,2-cyclohexanediamine (tpchxn), N-(6-methyl-2-pyridylmethyl)-N,N',N'-tris(2-pyridylmethyl)ethylenediamine (ltpen) and N,N'-bis(6-methyl-2-pyridylmethyl)-N,N'-bis(2-pyridylmethyl)ethylenediamine(blbpen) and their complexes with Fe(II), Co(III), and Ni(II) are prepd. Magnetic susceptibility measurements at 300-400 K of [FeL](ClO4)2.nH2O are reported (L = tppn, tptn, tpchxn, ltpen, blbpen, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (tpen)). The results show that the complexes of Fe(II) with L = tpen, tppn, and tpchxn exist in a temp.-dependent high-spin 5T2 .dblarw. low-spin 1A1 equil. with spin transition-temps. Tc = 380 K for [Fe(tpen)]2+, 492 K for [Fe(tppn)]2+, and 445 K for [Fe(tpchxn)]2+. The complexes of Fe(II) with L = tptn are low-spin and L = blbpen are high-spin over the temp. range investigated. The electronic spectra of the Fe(II) complexes show that the crit. value of Delta 1 (high-spin), where 1A1 becomes the ground state, is 12.6 kK in accordance with predictions based on the electronic spectra of the Ni(II) complexes. The 13C NMR spectra of the Co(III), Ru(II), and Zn(II) complexes demonstrate that the ligands are hexadentate and that the complexes have pseudooctahedral symmetry. [on SciFinder (R)]