Search

Reacting [MnIII(5-TMAM(R)-salmen)(H2O)2](ClO4)3·H2O with [MIII(CN)6]3− moieties yields a series of discrete cyano-bridged heterodinuclear complexes, [MnIII(5-TMAM(R)-salmen)(H2O)MIII(CN)6]·7H2O·MeCN (where 5-TMAM(R)-salmen=(R)-N,N′-(1-methylethylene)bis(5-trimethylammoniomethylsalicylideneiminate; M=Fe (1), Mn (2), and Cr (3)). dc magnetic susceptibility and magnetization studies on powdered samples showed that the MnIII(5-TMAM(R)-salmen) moiety had significant uniaxial anisotropy and that [MIII(CN)6]3− moieties of 1 and 2 had magnetic anisotropy due to unquenched orbital angular momenta, which significantly affects the magnetic behavior of this system. Frequency-dependent ac susceptibility signals indicated that slow magnetic relaxation was occurring, meaning that 1 and 2 behave as single-molecule magnets. [ABSTRACT FROM AUTHOR]

Abstract: Three novel Mn(III) cyclam complexes, [Mn(cyclam)(NCBH3)2](CF3SO3), [Mn(cyclam)(NCBPh3)2](CF3SO3), and [Mn(cyclam)(NCSe)2](CF3SO3)·H2O, have been synthesized. These complexes are in the high-spin state between 4 and 350K, and show large zero-field splittings. The crystal structure of [Mn(cyclam)(NCBH3)2](CF3SO3) was determined where the axial elongation of Mn–N bonds is found to be the largest among the homologue complexes. Ligand field in the [Mn(cyclam)X2]+ complex series was examined by angular-overlap model calculation. [Copyright &y& Elsevier]

Abstract: The reactions of 2-hydroxyphenylethanone oxime (Me-H2salox) and (2-hydroxy-phenyl)-phenyl-methanone oxime (Ph-H2salox) with Mn(ClO4)2·6H2O in MeOH afford trinuclear manganese complexes of [Mn3O(Me-salox)3(MeOH)3(ClO4)]·MeOH (1·MeOH) and [Mn3O(Ph-salox)3(MeOH)3(ClO4)]·2MeOH (2·2MeOH), respectively. X-ray analysis shows that both complexes contain a manganese triangle core, [MnIII 3O]7+. The structural distortion from the twisting of the oxime ligands dominates the ferromagnetic interactions within the three Mn ions in both compounds and results in an S = 6 ground state. The frequency dependence of out-of-phase signals in the alternating current (AC) magnetic susceptibility measurements and the temperature-dependent and sweep-rate-dependent hysteresis loops are indicative of single-molecule magnet behavior. Moreover, both complexes show step-wise magnetization, indicating the occurrence of quantum tunneling of magnetization (QTM). Interestingly, a tail to tail arrangement in the crystal packing of complex 1·MeOH results in strong intermolecular H-bonding interactions and leads to the exchange-bias effect from the antiferromagnetic interaction between the adjacent Mn3 molecules. In contract, QTM steps of complex 2·2MeOH show an absence of the exchange-bias effect due to a weak intermolecular interaction from a head to tail arrangement. [Copyright &y& Elsevier]

The syntheses and physical properties are reported for three single-molecule magnets (SMMs) with the composition [Ni(hmp)(ROH)Cl]4, where R is CH3 (complex 1), CH2CH3 (complex 2) or CH2CH2C(CH3)3 (complex 3) and hmp− is the monoanion of 2-hydroxymethylpyridine. The core of each complex is a distorted cube formed by four NiII ions and four alkoxide hmp− oxygen atoms at alternating corners. Ferromagnetic exchange interactions give a S=4 ground state. Single crystal high-frequency EPR spectra clearly indicate that each of the complexes has a S=4 ground state and that there is negative magnetoanisotropy, where D is negative for the axial zero-field splitting DSˆz2. Magnetization versus magnetic field measurements made on single crystals with a micro-SQUID magnetometer indicate these Ni4 complexes are SMMs. Exchange bias is seen in the magnetization hysteresis loops for complexes 1 and 2. [Copyright &y& Elsevier]