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

Abstract

AbstractReaction of GdCl3(H2O)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(H2O)]∞, whereas treatment of HoCl3(H2O)6 with 1,3‐bis(pyridin‐2‐yl)propane‐1,3‐dione yielded a trinuclear cluster [Ho3(o‐dppd)3(μ3‐OH)2(H2O)4Cl2]Cl2. The compounds were characterised by elemental analysis, IR spectroscopy and magnetism, and their structures were investigated by X‐ray crystallography. The 8.20‐μB magnetic‐moment value of the polymeric [Gd(p‐dppd)3(H2O)]∞, between 300 and 20 K, and the magnetisation isotherms (2–20 K; fields 0–5 T), are in agreement with essentially uncoupled single‐ion Gd3+ f7 centres, a small decrease in μeff below 20 K being indicative of zero‐field splitting. A temperature‐dependent dc‐susceptibility and magnetisation investigation of the trinuclear (triangular) [Ho3(o‐dppd)3(μ3‐OH)2(H2O)4Cl2]Cl2 revealed that spin‐orbit and ligand‐field effects on the Ho3+ centres, leading to thermal depopulation of Zeeman levels and consequent decreases in μeff values with decreasing temperature, are occurring rather than weak intra‐cluster antiferromagnetic coupling. Frequency‐ and temperature‐dependent ac‐susceptibility studies on this homometallic Ho3+ 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 Dy3+ triangle having the same core structure but with different chelating {O,O} ligands.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)