Encouraging Chromium(III) Ions to Form Larger Clusters: Syntheses, Structures, Magnetic Properties and Theoretical Studies of Di- and Octametallic Cr Clusters
✍ Scribed by Caytie E. Talbot-Eeckelaers; Gopalan Rajaraman; Joan Cano; Guillem Aromí; Eliseo Ruiz; Euan K. Brechin
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 270 KB
- Volume
- 2006
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Reaction of anhydrous CrCl~2~ with the tripodal ligands 1,1,1‐tris(hydroxymethyl)ethane (H~3~thme), 1,1,1‐tris(hydroxymethyl)propane (H~3~tmp) and pentaerythritol (H~4~peol) produces three new Cr^III^ clusters that have been structurally and magnetically characterised. The dimeric complex [Cr~2~(H~2~tmp)~2~Cl~4~]·2MeOH (1·2MeOH) is generated under reflux. An analogous reaction, but under solvothermal conditions produces the octametallic species [Cr~8~O~2~(thme)~2~(Hthme)~4~Cl~6~]·2MeOH (2·2MeOH) and [Cr~8~O~2~(Hpeol)~2~(H~2~peol)~4~Cl~6~]·3MeOH (3·3MeOH). Complex 1 is a simple dimeric species whereas the structures of 2 and 3 are based on the decametallate {M~10~O~28~}^26–^ ion. Variable‐temperature direct‐current (dc) magnetic susceptibility data were collected for complexes 1 and 2 in the 1.8–300 K temperature range in fields up to 5.0 T. Complex 1 has a ground state of S = 0 with the best‐fit parameters J = –12.30 ± 0.04 cm^–1^ and g = 1.990 ± 0.003. Electronic structure calculations based on density functional theory (DFT) on 1 and 2 have been carried out and good agreement with the experimental data was found for 1. For 2, the theoretical results have been used as starting point to fit the J values to the experimental data, revealing the presence of competing antiferromagnetic (J~4,7~ = –39.0 cm^–1^; J~3,7~ = J~4,6~ = +1.1 cm^–1^, J~4,5~ = J~3,4~ = –20.0 cm^–1^, J~3,6~ = –16.0 cm^–1^ and J~1,3~ = J~1,6~ = J~1,4~ = J~1,7~ = –4.8 cm^–1^) exchange interactions between the Cr^III^ centres that suggests a singlet ground state with very close S = 1, 2, 3 and 4 excited states. Magneto‐structural correlations developed on a model complex based on 1 show a strong dependence of J with Cr–O–Cr angle. A similar magneto‐structural correlation is found for the J values obtained by theoretical calculations on 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)