Encouraging Chromium(III) Ions to Form Larger Clusters: Syntheses, Structures, Magnetic Properties and Theoretical Studies of Di‐ and Octametallic Cr Clusters

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)