Synthesis and properties of [MII(L6)2][ClO4]2(M = Fe, Co and Ni): structures of Co and Ni complexes and spin-state transition by Fe complex (L6= 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine)

Singh, Shubha ; Mishra, Vibha ; Mukherjee, Jhumpa ; Seethalekshmi, N. ; Mukherjee, Rabindra Nath (2003) Synthesis and properties of [MII(L6)2][ClO4]2(M = Fe, Co and Ni): structures of Co and Ni complexes and spin-state transition by Fe complex (L6= 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine) Dalton Transactions (17). pp. 3392-3397. ISSN 1477-9226

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Official URL: http://pubs.rsc.org/en/Content/ArticleLanding/2003...

Related URL: http://dx.doi.org/10.1039/B305574D

Abstract

A new non-planar tridentate ligand 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine (L6) and its mononuclear bis-ligand complexes [M(L6)2][ClO4]2 [M = Fe (1), Co (2) and Ni (3)] have been synthesized. In the dications of six-co-ordinate complexes of 2 and 3, each L6 is arranged in a meridional mode. Structural analyses reveal that the M-Npyrazole bond length is appreciably shorter than the M-Npyridine bond lengths. Due to the weak field nature of L6 (absorption spectral analyses) towards Fe(II), Co(II) and Ni(II) the complexes are uniformly high-spin at room-temperature. Temperature-dependent magnetic susceptibility measurements reveal that while Co(II) and Ni(II) complexes remain high-spin over the entire range investigated (6-300 K for 2 and 63-300 K for 3), the Fe(II) complex exhibits a temperature-induced (5.2-300 K) spin transition in going from the S = 2 state at 300 K to predominantly an S = 0 state below 80 K. From the linear ln Keq [1A1 (ls) ↔ 5T2 (hs)] vs. 1/T relationship (190-250 K) the derived thermodyanamic parameters are: ΔH = 9.7 ± 0.04 kJ mol-1 and ΔS = 56 ± 0.18 J K-1 mol-1. While complex 1 displays in MeCN an irreversible MIII/MII redox process [anodic peak potential, Epa = 1.06 V vs. SCE], for complex 2 such a redox process is reversible [E½ = 0.74 V vs. SCE and ΔEp = 80 mV].

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Deposited On:04 Dec 2010 10:48
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