Cu - O - Cu superexchange of some polyolate-bridged copper(II) clusters

Abstract

The magnetic properties of two tris-{µ-propanetriolato(3-)} tricuprate clusters:2); and of a polyolato metallate cluster of sixteen Cu 2+ ions: Li 8 [Cu 16 (C 6 H 8 O 6 ) 4 (C 6 H 10 O 6 ) 4 ]•44H 2 O ( 3) are investigated. The Cu-O-Cu intracluster superexchange constants determined by measurements of the magnetic susceptibility are antiferromagnetic. They depend strongly on the corresponding Cu-O-Cu bonding angle and take values up to 400 cm −1 . The interplay of exchange narrowing and dipolar, hyperfine and g-anisotropy broadening for clusters of strongly exchange coupled Cu 2+ ions is studied using electron spin resonance (ESR) at 9.5 GHz and 245 GHz.

New concepts for molecular magnets

“…Inset: schematic structure of 1 and 2. Dots: experimental results, solid lines: calculation (Pilawa and Schuhmacher 1996). parallel orientation of the magnetic field are observed at the high-field side of the spectra.…”

“…The analysis of the magnetic susceptibility of the two tris-{m-propanetriolato(3-)} tricuprate clusters Li 3 [Cu 3 (m-C 3 H 5 O 3 ) 3 ] 18H 2 O (1) and Na 3 [Cu 3 (m-C 3 H 5 O 3 ) 3 ] 9H 2 O (2) is shown in Fig. 45 (Klaassen and Klu È fers 1993, Klu È fers and Schuhmacher 1994, Pilawa and Schuhmacher 1996. The complex 1 is characterized by a threefold symmetry axis with a 120X8 and Jak B À60 K. 2 is characterized by a mirror plane so that there are two bridging angles a 125 and 145 , which lead to the exchange constants J 1 ak B À60 K and J 2 ak B À648 K, respectively.…”

“…For non-symmetric trinuclear spin s 1a2 compounds the degeneracy of the spin terms S 1a2 is removed. The eigenvalues of the spin Hamiltonian (Pilawa and Schuhmacher 1996).…”

“…The exchange interaction is also influenced by the chemical surrounding of the oxygen atom. The analysis of the magnetic susceptibility of the two tris-{m-propanetrio- (Klaassen and Klu È fers 1993, Klu È fers and Schuhmacher 1994, Pilawa and Schuhmacher 1996. The complex 1 is characterized by a threefold symmetry axis with a 120X8 and Jak B À60 K. 2 is characterized by a mirror plane so that there are two bridging angles a 125 and 145 , which lead to the exchange constants J 1 ak B À60 K and J 2 ak B À648 K, respectively.…”

“…In the following paragraphs the magnetic properties of four different kinds of spin cluster compounds are discussed. Spin cluster 1 represents a torus which is formed by an triangular network of Cu II ions Schuhmacher 1994, Pilawa andSchuhmacher 1996). The mixed valence manganese spin cluster 3 displays a super- paramagneticlike behavior at low temperatures (Pilawa et al 1998b).…”