Formation of Ho III Trinuclear Clusters and Gd III Monodimensional Polymers Induced by ortho and para Regioisomers of Pyridyl‐Functionalised β‐Diketones: Synthesis, Structure, and Magnetic Properties

Reaction of GdCl 3 (H 2 O) 6 and 1,3‐bis(pyridin‐4‐yl)propane‐1,3‐dione in methanol with an excess of triethylamine produced a monodimensional polymeric chain [Gd( p ‐dppd ) 3 (H 2 O)] ∞ , whereas treatment of HoCl 3 (H 2 O) 6 with 1,3‐bis(pyridin‐2‐yl)propane‐1,3‐dione yielded a trinuclear cluster [Ho 3 ( o ‐dppd ) 3 (μ 3 ‐OH) 2 (H 2 O) 4 Cl 2 ]Cl 2 . The compounds were characterised by elemental analysis, IR spectroscopy and magnetism, and their structures were investigated by X‐ray crystallography. The 8.20‐μ B magnetic‐moment value of the polymeric [Gd( p ‐dppd ) 3 (H 2 O)] ∞ , between 300 and 20 K, and the magnetisation isotherms (2–20 K; fields 0–5 T), are in agreement with essentially uncoupled single‐ion Gd 3+ f 7 centres, a small decrease in μ eff below 20 K being indicative of zero‐field splitting. A temperature‐dependent dc‐susceptibility and magnetisation investigation of the trinuclear (triangular) [Ho 3 ( o ‐dppd ) 3 (μ 3 ‐OH) 2 (H 2 O) 4 Cl 2 ]Cl 2 revealed that spin‐orbit and ligand‐field effects on the Ho 3+ centres, leading to thermal depopulation of Zeeman levels and consequent decreases in μ eff values with decreasing temperature, are occurring rather than weak intra‐cluster antiferromagnetic coupling. Frequency‐ and temperature‐dependent ac‐susceptibility studies on this homometallic Ho 3+ cluster did not show clear evidence for slow magnetisation reversal, characteristic of single‐molecule magnetism (SMM), and this contrasts with such behaviour recently reported, elsewhere, for a Dy 3+ triangle having the same core structure but with different chelating { O , O } ligands.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)