Enhanced Vapor-Phase Processing in Fluorinated Fe4Single-Molecule Magnets

A new tetrairon(III) single-molecule magnet with enhanced volatility and processability was obtained by partial fluorination of the ancillary beta-diketonato ligands. Fluorinated proligand Hpta = pivaloyltrifluoroacetone was used to assemble the bis(alkoxido)-bridged dimer [Fe-2(OEt)(2)(pta)(4)] (1) in crystalline form, from which the new tetranuclear complex [Fe-4(L)(2)(pta)(6)] (2) was synthesized in a one-pot reaction with H3L = 2-hydroxymethyl-2-phenylpropane-1,3-diol, NaOEt, and FeCl3 in a Et2O:EtOH solvent mixture. The structure of compound 2 was inferred from H-1 NMR, mass spectrometry, magnetic measurements, and DFT calculations. Direct current magnetic data are consistent with the expected metal-centered triangular topology for the iron(III) ions, with an antiferromagnetic coupling constant J = 16.20(6) cm(-1) between the central iron and the peripheral ones and consequent stabilization of an S = 5 spin ground state. Alternating current (ac) susceptibility measurements in 0 and 1 kOe static applied fields show the presence of a thermally activated process for magnetic relaxation, with tau(0) = 2.3(1) 10(-7) s and U-eff/k(B) = 9.9(1) K at zero static field and tau(0) = 2.0(2) 10(-7) s and U-eff/k(B) = 13.0(2) K at 1 kOe. At a pressure of 10(-7) mbar, compound 2 sublimates at (440 +/- 5) K vs (500 +/- 10) K for the nonfluorinated variant [Fe-4(L)(2)(dpm)(6)] (Hdpm = dipivaloylmethane). According to XPS, ToF-SIMS, and ac susceptibility studies, the chemical composition, fragmentation pattern, and slow magnetic relaxation of the pristine material are retained in sublimated samples, suggesting that the molecular structure remains totally unaffected upon vapor-phase processing.