Exchange and Double-Exchange Phenomena in Linear Homo- and Heterotrinuclear Nickel(II,III,IV) Complexes Containing Six 2-Ph
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- 作者：Thomas Beissel ; Frank Birkelbach ; Eckhard Bill ; Thorsten Glaser ; Frank Kesting ; Carsten Krebs ; Thomas Weyhermü ; ller ; Karl Wieghardt ; Christian Butzlaff ; and Alfred X. Trautwein
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：December 11, 1996
- 年：1996
- 卷：118
- 期：49
- 页码：12376 - 12390
- 全文大小：756K
- 年卷期：v.118,no.49(December 11, 1996)
- ISSN：1520-5126
文摘
A series of homo- and heterotrinuclear complexescontaining three face-sharing octahedra has beensynthesized by using the pendent arm macrocyclic ligands1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, L0H3, and1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane,LH3:[{L0NiII}2NiII](1) and[{LCoIII}2CoIII](PF6)3(2);[{LCoIII}2Ni]n+(n = 2 (3), 3 (4), 4(5));[{LNi}2CoIII]n+(n = 1 (6), 2 (7), 3 (8))and itslinkage isomers[{LNi}Ni{CoIIIL}]n+(n = 1 (9), 2 (10), 3(11)) and, finally, the complexes[{LNi}2Ni]n+ (n= 0(12), 1 (13), 2 (14), 3(15)). In complex 1 three octahedralNiII ions form a linear array with two terminal[L0NiII]-moieties in a facial N3O3 donor set and acentral NiII ion which is connected to the terminal ionsvia six phenolatebridging pendent arms of L0. In complexes2-15 the three metal ions are always in thesame ligand matrix yieldinganN3M(
-S)3M(-S)3MN3first-coordination sphere regardless of the nature of the metal ions(nickel or cobalt) ortheir formal oxidation states. From temperature dependent magneticsusceptibility measurements it has been determinedthat 1 has an S = 3 ground state whereas in12 it is S = 1. In order to understandthis difference in exchangecoupling (ferromagnetic in 1 and antiferromagnetic in12) in two apparently very similar complexes themagneticproperties of 2-15 have been investigated.Complex 3 has an S = 1 and 4 anS = 1/2, and 5 isdiamagnetic (S =0) as is its isoelectronic counterpart 2. Thisindicates the availability of the oxidation states II, III, and IV ofthecentral NiS6 unit. In the isostructural complexes6, 7, and 8, two terminal nickel ionsare bridged by a centraldiamagnetic CoIII. The exchange coupling between twoterminal paramagnetic nickel ions was studied as afunctionof their formal oxidation state. In 6 the twoNiII ions are ferromagnetically coupled (S =2); the mixed-valentNiIINiIII species 7 has anS = 3/2 ground state and in8 most probably two NiIII ions (d7low spin) give rise to an S= 1 ground state. In contrast, in the series 9,10, and 11 where two nickel ions are in aposition adjacent to eachother 9 has an S = 0 (antiferromagneticcoupling), but in the mixed-valent complex 10 anS = 3/2 ground state(ferromagnetic coupling) is observed. In 11 anS = 1 ground state prevails which may be achieved byferromagneticcoupling between two NiIII ions. For the trinuclearnickel complexes 12-15 an S = 1ground state has been determinedfor 12, an S = 3/2 forthe mixed valent complex 13, and an S = 2 for14, and 15 exhibits an S =3/2 ground state.The Goodenough-Kanamori rules do not provide a consistentexplanation for the observed ground states in allcases. The concept of double exchange, originally introduced byZener in 1951, appears to provide a more appropriatedescription for the mixed-valent species 7, 10,13, 14, and 15. This picture iscorroborated by the electrochemistryand EPR spectroscopy of complexes.
-S)3M(-S)3MN3first-coordination sphere regardless of the nature of the metal ions(nickel or cobalt) ortheir formal oxidation states. From temperature dependent magneticsusceptibility measurements it has been determinedthat 1 has an S = 3 ground state whereas in12 it is S = 1. In order to understandthis difference in exchangecoupling (ferromagnetic in 1 and antiferromagnetic in12) in two apparently very similar complexes themagneticproperties of 2-15 have been investigated.Complex 3 has an S = 1 and 4 anS = 1/2, and 5 isdiamagnetic (S =0) as is its isoelectronic counterpart 2. Thisindicates the availability of the oxidation states II, III, and IV ofthecentral NiS6 unit. In the isostructural complexes6, 7, and 8, two terminal nickel ionsare bridged by a centraldiamagnetic CoIII. The exchange coupling between twoterminal paramagnetic nickel ions was studied as afunctionof their formal oxidation state. In 6 the twoNiII ions are ferromagnetically coupled (S =2); the mixed-valentNiIINiIII species 7 has anS = 3/2 ground state and in8 most probably two NiIII ions (d7low spin) give rise to an S= 1 ground state. In contrast, in the series 9,10, and 11 where two nickel ions are in aposition adjacent to eachother 9 has an S = 0 (antiferromagneticcoupling), but in the mixed-valent complex 10 anS = 3/2 ground state(ferromagnetic coupling) is observed. In 11 anS = 1 ground state prevails which may be achieved byferromagneticcoupling between two NiIII ions. For the trinuclearnickel complexes 12-15 an S = 1ground state has been determinedfor 12, an S = 3/2 forthe mixed valent complex 13, and an S = 2 for14, and 15 exhibits an S =3/2 ground state.The Goodenough-Kanamori rules do not provide a consistentexplanation for the observed ground states in allcases. The concept of double exchange, originally introduced byZener in 1951, appears to provide a more appropriatedescription for the mixed-valent species 7, 10,13, 14, and 15. This picture iscorroborated by the electrochemistryand EPR spectroscopy of complexes.