Issue 9, 2002
From the journal:

Journal of the Chemical Society, Dalton Transactions

Exchange-coupled high-spin, low-spin and spin-crossover dicobalt(ii) complexes of a pyridazine-containing Schiff-base macrocycle: control of cobalt(ii) spin state by choice of axial ligands

Sally Brooker,*a   Duncan J. de Geest,a   Robert J. Kelly,a   Paul G. Plieger,a   Boujemaa Moubaraki,b   Keith S. Murray*b  and  Geoffrey B. Jamesonc  

* Corresponding authors

a Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand
E-mail: sbrooker@alkali.otago.ac.nz

b School of Chemistry, Monash University, PO Box 23, Clayton, Victoria 3800, Australia

c Institute of Fundamental Sciences, Chemistry, Massey University, PO Box 11222, Palmerston North, New Zealand

Abstract

A series of doubly pyridazine-bridged dicobalt(II) macrocyclic complexes, 1–7, is reported. The pyridazine-containing Schiff-base macrocycle L1 [derived from the (2 + 2) condensation of 3,6-diformylpyridazine and 1,3-diaminopropane] provides four nitrogen donor atoms, disposed in an approximately square-planar manner, to each cobalt ion. Variation of the axial donors alters the spin state of the cobalt(II) ions from high spin, [Co2L1(H2O)4](ClO4)4 (2), [Co2L1(H2O)4](S2O6)2·4(H2O) (3·8H2O), [Co2L1(N3)2](ClO4)2 (4) and [Co2L1(NCO)3]ClO4 (5), to spin crossover, [Co2L1(MeCN)4](ClO4)4 (1·4MeCN) and [Co2L1(NCS)2(SCN)2] (6), to low spin, [Co2L1Cl2](ClO4)2 (7). Detailed magnetic susceptibility studies have yielded small, negative 2J values (−7 to −20 cm−1) for complexes 2 to 5. Compounds 1, 1·4MeCN and 6 are rare examples of binuclear complexes displaying simultaneous spin crossover (3/2 ⇔ 1/2) at high temperatures and antiferromagnetic exchange of the low-spin d7–d7 ions at low temperatures (2J = −10 to −14 cm−1).

Graphical abstract: Exchange-coupled high-spin, low-spin and spin-crossover dicobalt(ii) complexes of a pyridazine-containing Schiff-base macrocycle: control of cobalt(ii) spin state by choice of axial ligands

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Article information

DOI
https://doi.org/10.1039/B111267H
Article type
Paper
Submitted
11 Dec 2001
Accepted
19 Feb 2002
First published
02 Apr 2002

J. Chem. Soc., Dalton Trans., 2002, 2080-2087

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Exchange-coupled high-spin, low-spin and spin-crossover dicobalt(II) complexes of a pyridazine-containing Schiff-base macrocycle: control of cobalt(II) spin state by choice of axial ligands

S. Brooker, D. J. de Geest, R. J. Kelly, P. G. Plieger, B. Moubaraki, K. S. Murray and G. B. Jameson, J. Chem. Soc., Dalton Trans., 2002, 2080 DOI: 10.1039/B111267H

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