Butterfly M₂^IIIEr₂ (M^III = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of <i>N</i>-(2-pyridylmethyl)­iminodiethanol (H₂L, pmide), FeCl₂·4H₂O or AlCl₃·6H₂O with ErCl₃·6H₂O and <i>p</i>-Me-PhCO₂H in the ratio of 2:1:1:4 in the presence of Et₃N in MeOH and MeCN yielded compounds [Fe₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>1</b>) and [Al₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>2</b>). These two complexes are isostructural, possessing a planar butterfly motif with the Er^III ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al₂Er₂] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe₂Er₂] compound reveals that the Fe–Fe and Fe–Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al₂Er₂] case

Butterfly M₂^IIIEr₂ (M^III = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of <i>N</i>-(2-pyridylmethyl)­iminodiethanol (H₂L, pmide), FeCl₂·4H₂O or AlCl₃·6H₂O with ErCl₃·6H₂O and <i>p</i>-Me-PhCO₂H in the ratio of 2:1:1:4 in the presence of Et₃N in MeOH and MeCN yielded compounds [Fe₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>1</b>) and [Al₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>2</b>). These two complexes are isostructural, possessing a planar butterfly motif with the Er^III ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al₂Er₂] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe₂Er₂] compound reveals that the Fe–Fe and Fe–Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al₂Er₂] case

Butterfly M₂^IIIEr₂ (M^III = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of <i>N</i>-(2-pyridylmethyl)­iminodiethanol (H₂L, pmide), FeCl₂·4H₂O or AlCl₃·6H₂O with ErCl₃·6H₂O and <i>p</i>-Me-PhCO₂H in the ratio of 2:1:1:4 in the presence of Et₃N in MeOH and MeCN yielded compounds [Fe₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>1</b>) and [Al₂Er₂(μ₃-OH)₂(pmide)₂(<i>p</i>-Me-PhCO₂)₆]·2MeCN (<b>2</b>). These two complexes are isostructural, possessing a planar butterfly motif with the Er^III ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al₂Er₂] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe₂Er₂] compound reveals that the Fe–Fe and Fe–Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al₂Er₂] case

Slow Magnetic Relaxation in Trigonal-Planar Mononuclear Fe(II) and Co(II) Bis(trimethylsilyl)amido ComplexesA Comparative Study

Alternating current magnetic investigations on the trigonal-planar high-spin Co²⁺ complexes [Li­(15-crown-5)] [Co­{N­(SiMe₃)₂}₃], [Co­{N­(SiMe₃)₂}₂(THF)] (THF = tetrahydrofuran), and [Co­{N­(SiMe₃)₂}₂(PCy₃)] (Cy = −C₆H₁₃ = cyclohexyl) reveal that all three complexes display slow magnetic relaxation at temperatures below 8 K under applied dc (direct current) fields. The parameters characteristic for their respective relaxation processes such as effective energy barriers <i>U</i>_eff (16.1(2), 17.1(3), and 19.1(7) cm^–1) and relaxation times τ₀ (3.5(3) × 10^–7, 9.3(8) × 10^–8, and 3.0(8) × 10^–7 s) are almost the same, despite distinct differences in the ligand properties. In contrast, the isostructural high-spin Fe²⁺ complexes [Li­(15-crown-5)] [Fe­{N­(SiMe₃)₂}₃] and [Fe­{N­(SiMe₃)₂}₂(THF)] do not show slow relaxation of the magnetization under similar conditions, whereas the phosphine complex [Fe­{N­(SiMe₃)₂}₂(PCy₃)] does, as recently reported by Lin et al. (Lin, P.-H.; Smythe, N. C.; Gorelsky, S. I.; Maguire, S.; Henson, N. J.; Korobkov, I.; Scott, B. L.; Gordon, J. C.; Baker, R. T.; Murugesu, M. <i>J. Am. Chem. Soc.</i> <b>2011</b>, <i>135</i>, 15806.) Distinctly differing axial anisotropy <i>D</i> parameters were obtained from fits of the dc magnetic data for both sets of complexes. According to density functional theory (DFT) calculations, all complexes possess spatially nondegenerate ground states. Thus distinct spin–orbit coupling effects, as a main source of magnetic anisotropy, can only be generated by mixing with excited states. This is in line with significant contributions of excited determinants for some of the compounds in complete active space self-consistent field (CASSCF) calculations done for model complexes. Furthermore, the calculated energetic sequence of d orbitals for the cobalt compounds as well as for [Fe­{N­(SiMe₃)₂}₂(PCy₃)] differs significantly from the prediction by crystal field theory. Experimental and calculated (time-dependent DFT) optical spectra display characteristic d–d transitions in the visible to near-infrared region. Energies for lowest transitions range from 0.19 to 0.35 eV; whereas, for [Li­(15-crown-5)]­[Fe­{N­(SiMe₃)₂}₃] a higher value is found (0.66 eV). Zero-field ⁵⁷Fe Mößbauer spectra of the three high-spin iron complexes exhibit a doublet at 3 K with small and similar values of the isomer shifts (δ), ranging between 0.57 and 0.59 mm/s, as well as an unusual small quadrupole splitting (Δ<i>E</i>_Q = 0.60 mm/s) in [Li­(15-crown-5)]­[Fe­{N­(SiMe₃)₂}₃]

Field-Induced Slow Magnetic Relaxation in the Ni(I) Complexes [NiCl(PPh₃)₂]·C₄H₈O and [Ni(N(SiMe₃)₂)(PPh₃)₂]

Direct current (dc) and alternating current (ac) magnetic measurements have been performed on the three Ni­(I) complexes: [NiCl­(PPh₃)₃], [NiCl­(PPh₃)₂]·C₄H₈O, and [Ni­(N­(SiMe₃)₂)­(PPh₃)₂]. Fits of the dc magnetic data suggest an almost similar behavior of the three compounds, which display only moderate deviations from the spin-only values. The ac magnetic investigations reveal that the two complexes with trigonal planar coordination[NiCl­(PPh₃)₂]·C₄H₈O and [Ni­(N­(SiMe₃)₂)­(PPh₃)₂]display slow magnetic relaxation at low temperatures under applied dc fields, whereas tetrahedral [NiCl­(PPh₃)₃] does not. Ground and excited states as well as magnetic data were calculated by ab initio wave function based multi-configurational methods, including dynamic correlation as well as spin–orbit coupling. The two trigonal planar complexes comprise well-isolated <i>S</i> = ¹/₂ ground states, whereas two <i>S</i> = ¹/₂ states with a splitting of less than 100 cm^–1 were found in the tetrahedral compound

Molecular Iron(III) Phosphonates: Synthesis, Structure, Magnetism, and Mössbauer Studies

The reaction of Fe­(ClO₄)₂·6H₂O with <i>t</i>-BuPO₃H₂ or Cl₃CPO₃H₂ in the presence of an ancillary pyrazole phenolate as a coligand, H₂phpzH [H₂phpzH = 3(5)-(2-hydroxyphenyl)­pyrazole], afforded tetra- and pentanuclear Fe­(III) phosphonate complexes [Fe₄(<i>t</i>-BuPO₃)₄(HphpzH)₄]·5CH₃CN·5CH₂Cl₂ (<b>1</b>) and [HNEt₃]₂[Fe₅(μ₃-O)­(μ-OH)₂ (Cl₃CPO₃)₃­(HphpzH)₅­(μ-phpzH]·3CH₃CN·2H₂O (<b>2</b>). Single-crystal X-ray structural analysis reveals that <b>1</b> possesses a cubic double-4-ring (D4R) core similar to what is found in zeolites. The molecular structure of <b>2</b> reveals it to be pentanuclear. It crystallizes in the chiral <i>P</i>1 space group. Magnetic studies on <b>1</b> and <b>2</b> have also been carried out, which reveal that the bridging phosphonate ligands mediate weak antiferromagnetic interactions between the Fe­(III) ions. Magnetization dynamics of <b>1</b> and <b>2</b> have been corroborated by a Mössbauer spectroscopy analysis

Spontaneous Resolution in Homochiral Helical [Ln(nic)₂(Hnic)(NO₃)] Coordination Polymers Constructed from a Rigid Non-chiral Organic Ligand

A series of homochiral lanthanide nicotinate helical coordination polymers [Ln^III(nic)₂(Hnic)­(NO₃)] (Ln = Eu (<b>1</b>), Gd (<b>2</b>), Tb (<b>3</b>); Hnic = nicotinic acid) has been solvothermally synthesized using nicotinic acid. In the resulting chains, chirality is not induced by a chiral agent but appears spontaneously <i>via</i> intrachain hydrogen bondings. Compounds <b>2</b> and <b>3</b> were magnetically characterized, and luminescent properties were observed for compounds <b>1</b> and <b>3</b>

Developing a “Highway Code” To Steer the Structural and Electronic Properties of Fe^III/Dy^III Coordination Clusters

In the recently established field of 3d/4f coordination cluster (CC) chemistry several burning questions still need to be addressed. It is clear that combining 3d and 4f metal ions within a coordination cluster core has the potential to lead to electronic structures that will be very difficult to describe but can also be extremely interesting. Furthermore, understanding why certain core topologies seem to be favored is difficult to predict. Here we show that the secondary coordination sphere provided by the ligands influences the favored product, as demonstrated for the compound [Fe₄Dy₂(μ₃-OH)₂(<i>n-</i>bdea)₄­(C₆H₅CO₂)₈]·MeCN (<b>1</b>), which has a 2Fe:2Dy:2Fe core and was made using [Fe^III₃O­(C₆H₅)­CO₂)­(L)₃]⁺ as starting material plus Dy­(NO₃)₃ and <i>N</i>-<i>n</i>-butyl-diethanolamine (<i>n-</i>bdeaH₂), compared with the compound made using a methyl meta-substituent (R) on the phenyl ring of the benzoate, [Fe^III₃O­(C₆H₄Me)­CO₂)­(L)₃]⁺ as starting material, which resulted in the “square-in-square” compound [Fe₄Dy₄(μ₃-OH)₄(<i>n-</i>bdea)₄­(O₂CC₆H₄CH₃)₁₂]·MeCN (<b>2</b>) when using ambient conditions. Changing reaction conditions from ambient to solvothermal leads to “double-propeller” compounds [Fe₄Dy₄(μ₄-O)₃(<i>n-</i>bdea)₃­(C₆H₅CO₂)₁₂]·13MeCN (<b>3</b>) and [Fe₄Dy₄(μ₄-O)₃(<i>n-</i>bdea)₃­(O₂CC₆H₄CH₃)₁₂]·MeCN (<b>4</b>) forming with this core, resulting irrespective of the substitution on the iron benzoate starting material. Furthermore, compounds <b>1</b> and <b>2</b> can be transformed into compounds <b>3</b> and <b>4</b>, respectively, using a solvothermal method. Thus, compounds <b>3</b> and <b>4</b> appear to be the thermodynamically most stable species. The factors steering the reactions toward these products are discussed. The electronic structures have been investigated using magnetic and Mössbauer studies. All compounds are cooperatively coupled 3d/4f systems, with compound <b>1</b> showing single-molecule magnet behavior

Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism

The Schiff-base proligand 4-<i>tert</i>-butyl-2,6-bis-[(2-hydroxy-phenylimino)­methyl]­phenol (H₃L) was prepared in situ from 4-<i>tert</i>-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H₃L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy₄(L)₃(DBM)₄]­[Et₃NH]} (<b>1</b>) and pentanuclear compound {[Dy₅(μ₃-OH)₂(L)₃(DBM)₄(MeOH)₄]·4­(MeOH)} (<b>2</b>) were obtained from the ligand (L)^3– and dibenzoylmethane. The tetranuclear compounds {[Dy₄(μ₄-OH)­(L)₂(acac)₄(MeOH)₂(EtOH)­(H₂O)]·(NO₃)·2­(MeOH)·3­(EtOH)} (<b>3</b>) and {[Ln₄(μ₃-OH)₂(L)­(HL)­(acac)₅(H₂O)] (HNEt₃)­(NO₃)·2­(Et₂O)} (Ln = Tb (<b>4</b>), Dy (<b>5</b>), Ho (<b>6</b>), and Tm (<b>7</b>)) resulted when the ligand (L)^3– was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound <b>1</b> adopts a linear arrangement of metal atoms, while tetranuclear compound <b>3</b> has a square grid arrangement of metal atoms, and tetranuclear compounds <b>4</b>–<b>7</b> have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound <b>1</b> and <b>3</b>–<b>7</b> is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds <b>1</b> suggest the presence of weak ferromagnetic interactions, whereas compounds <b>2</b>–<b>6</b> exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds <b>1</b>,<b> 2</b>, and <b>3</b> also show single-molecule magnet behavior under an applied dc field

Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism

The Schiff-base proligand 4-<i>tert</i>-butyl-2,6-bis-[(2-hydroxy-phenylimino)­methyl]­phenol (H₃L) was prepared in situ from 4-<i>tert</i>-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H₃L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy₄(L)₃(DBM)₄]­[Et₃NH]} (<b>1</b>) and pentanuclear compound {[Dy₅(μ₃-OH)₂(L)₃(DBM)₄(MeOH)₄]·4­(MeOH)} (<b>2</b>) were obtained from the ligand (L)^3– and dibenzoylmethane. The tetranuclear compounds {[Dy₄(μ₄-OH)­(L)₂(acac)₄(MeOH)₂(EtOH)­(H₂O)]·(NO₃)·2­(MeOH)·3­(EtOH)} (<b>3</b>) and {[Ln₄(μ₃-OH)₂(L)­(HL)­(acac)₅(H₂O)] (HNEt₃)­(NO₃)·2­(Et₂O)} (Ln = Tb (<b>4</b>), Dy (<b>5</b>), Ho (<b>6</b>), and Tm (<b>7</b>)) resulted when the ligand (L)^3– was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound <b>1</b> adopts a linear arrangement of metal atoms, while tetranuclear compound <b>3</b> has a square grid arrangement of metal atoms, and tetranuclear compounds <b>4</b>–<b>7</b> have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound <b>1</b> and <b>3</b>–<b>7</b> is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds <b>1</b> suggest the presence of weak ferromagnetic interactions, whereas compounds <b>2</b>–<b>6</b> exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds <b>1</b>,<b> 2</b>, and <b>3</b> also show single-molecule magnet behavior under an applied dc field