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The employment of the [1+1] condensation approach for the preparation of new macrocyclic scaffolds (LN6 and LN3O3) towards high-performance Dy(III) single-molecule magnets (SMMs) with pseudo-D6h symmetry is described. Engineering of the macrocycles denticity from LN6 to LN3O3 leads to a mononuclear SMM with a large Ueff value of 1300 K. The experimental results are supported by ab initio calculations, which indicate relaxation of the magnetization via the second-excited state. [ABSTRACT FROM AUTHOR]

The combined use of 2-(2-pyridyl)-1,3-propane-diol (pypdH2) and 2-hydroxymethyl-2-(2-pyridyl)-1,3-propane-diol (pyptH3) in Cu2+/4f chemistry has afforded a new family of isostructural [Cu6M4(pypt)4(pypdH)4(NO3)8] [M = Gd (1), Tb (2), Dy (3), and Y (4)] complexes. These compounds are based on an unprecedented three-layered symmetric [Cu6M4(μ-OR)16]8+ structural core, formed from the connection of the metal ions by bridging alkoxide arms of the organic ligands. Direct current magnetic susceptibility studies for complexes 1–3 revealed the presence of dominant ferromagnetic exchange interactions, suggesting the existence of large spin ground state values. Alternating current magnetic studies indicate the presence of slow-magnetic relaxation in 1–3. [ABSTRACT FROM AUTHOR]

The first use of the organic chelate N-hydroxy-1,8-naphthalimide (hynadH) in DyIII chemistry has unveiled access to a synthetic 'playground' composed of four new dinuclear complexes, all of which possess the same planar {Dy2(µ-OR)2}4+ diamond-shaped core, resulting from the bridging and chelating capacity of the hynad-groups. The structural stability of the central {Dy2} core has allowed for the modulation of the peripheral coordination sites of the metal ions, and specifically the NO3 -/hynad-ratio of capping groups, thus affording the compounds [Dy2(hynad)2(NO3)4(DMF)2] (1), (Me4N)2[Dy2(hynad)2(NO3)6] (2), [Dy2(hynad)4(NO3)2(H2O)2] (3), and [Dy2(hynad)6(H2O)2] (4). Because of the chemical and structural modifications in the series 1-4, the DyIII coordination polyhedra are also dissimilar, comprising the muffin (1 and 3), tetradecahedral (2), and spherical tricapped trigonal prismatic (4) geometries. Complexes 1, 2, and 4 exhibit a ferromagnetic response at low temperatures, while 3 is antiferromagnetically coupled. All compounds exhibit out-of-phase (?''M) ac signals as a function of ac frequency and temperature, thus behaving as single-molecule magnets (SMMs), in the absence or presence of applied dc fields. Interestingly, the hynad--rich and nitrato-free complex 4, demonstrates the largest energy barrier (Ueff = 69.62(1) K) for the magnetization reversal which is attributed to the presence of the two axial triangular faces of the spherical tricapped trigonal prism by the negatively charged O-atoms of the hynad-ligands. [ABSTRACT FROM AUTHOR]

The synthesis, crystal structures, Mössbauer spectra and variable temperature dc and ac magnetic susceptibility studies of a new family of trinuclear heterometallic Fe3+/Ln3+ complexes, [Fe2Ln(PhCO2)3((py)2CO2)((py)2C(OMe)O)2(NO3)Cl] (Ln = Gd (1/Gd), Tb (1/Tb), Dy (1/Dy), and Ho (1/Ho)), where (py)2CO22− and (py)2C(OMe)O− are the anions of the gem-diol and hemiketal derivatives of di-2-pyridyl ketone, are reported. Compounds 1/Ln are based on an asymmetric "V-shaped" [Fe3+(μ-OR)Ln(μ-OR)2Fe3+]6+ structural core formed from the connection of the two terminal Fe3+ centers to the central Ln3+ ion either through one or two alkoxide groups originating from the alkoxide-type bridging ligands. Direct current magnetic susceptibility studies reveal the presence of weak antiferromagnetic interactions between the Fe3+ ions. Alternating current magnetic studies indicate the presence of a slow-magnetic relaxation process in 1/Dy with an energy barrier Ueff = 6.7 (±0.3) K and a pre-exponential factor, τ0 = 2.2 (±0.4) × 10−7 s. The electronic, magnetic and relaxation properties of the complexes were further monitored by variable temperature 57Fe Mössbauer spectroscopy. At T > 80 K the spectra from the complexes comprise two quadrupole doublets the hyperfine parameters of which reflect the distinct coordination environment of the two Fe3+ terminal sites. At T < 20 K, the Mössbauer spectra for 1/Dy are affected by magnetic relaxation effects. At 1.5 K, the spectrum of 1/Dy comprises well defined magnetic sextets indicating relaxation times slower than the characteristic time of the Mössbauer technique (10−7 s) in agreement with the dynamic magnetic measurements. 1/Gd exhibits broad unresolved magnetic sextets at 1.5 K indicating that the spin relaxation time is of the order of the Mössbauer characteristic time at this temperature. For 1/Tb, 1/Ho the Mössbauer spectra exhibit slight broadening even at the lowest available temperature consistent with magnetic relaxation times less than 10−7 s. [ABSTRACT FROM AUTHOR]

A new family of radical-bridged compounds, (Cp*2Co)[M2Cl4(dpq)] (M = Fe (1), Co (2), Zn (3)), (dpq = 2,3-di(2-pyridyl)-quinoxaline) is reported. Magnetic studies, DFT and ab initio calculations reveal strong antiferromagnetic metal–radical interactions with coupling constants of J = −213.1 and −218.8 cm−1 for 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

Structural, magnetic and theoretical studies of three octahedral mononuclear DyIII complexes with triphenylphosphine oxide and halide ligands are reported. The Cl− and Br− analogues exhibit SMM behavior with energy barriers of 49.1 K and 70.9 K, respectively under a small dc field. Ab initio calculations were performed, the results of which predict higher energy barriers for iodide containing SMMs. [ABSTRACT FROM AUTHOR]

Self-assembly reactions of CoII ions in the presence of the 2,2-bipyrimidine (bpym) ligand produced both a dinuclear and an octanuclear cation with the nuclearity being governed by hydrogen-bonding versus anion–π interactions between the anions and the ligands. [ABSTRACT FROM AUTHOR]

Two new homoleptic DyIII compounds [Dy(TpMe2)2][DyCl3(TpMe2)]·CH2Cl2 (1) and [Dy(TpMe2)2]I (3) as well as a heteroleptic (NMe4)[DyCl3(TpMe2)] (2) (TpMe2 = tris(3,5-dimethylpyrazolyl)borate) species are reported. Magnetic studies revealed that 1 is a single-molecule magnet (SMM) with an energy barrier of Ueff = 80.7 K with τ0 = 6.2 × 10−7 s under a zero applied field. Compound 3 exhibits a Ueff of 13.5 K with τ0 = 1.6 × 10−6 s under a 0.08 T applied field. Ab initio CASSCF + RASSI-SO calculations were performed to further investigate the magnetic behavior of complexes 1–3. The results support experimental magnetic data for 1 and 3 and indicate that an intermolecular dipolar interaction of (zJ = −0.1 cm−1) is responsible for the SMM behavior of 1. [ABSTRACT FROM AUTHOR]

Two dinuclear lanthanide complexes (Gd and Dy) were prepared and characterized by X-ray, magnetic and computational methods. The Dy analogue shows SMM behavior with an energy barrier of 98.4 K in the absence of an applied dc field. Theoretical calculations were performed on model complexes which support the hypothesis that the energy barrier will increase if the soft-donor atoms S and Se are used in lieu of an O donor. [ABSTRACT FROM AUTHOR]

The synthesis of a new family of ferromagnetically-coupled {Ni10} clusters counterbalanced by various [Ln(NO3)5]2− ions is herein described. The resulting compounds are organic chelate-free and the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology reminiscent of the structure of the brucite mineral. [ABSTRACT FROM AUTHOR]

A new family of mononuclear lanthanide complexes, where the eight coordinate lanthanide ions adopt a very rare cubic coordination geometry is reported. The Dy analogue exhibits SMM behavior with a Ueff value 95.7 K under a 0.02 T applied dc field. Ab initio calculations support the observed magnetic behavior. [ABSTRACT FROM AUTHOR]

A new family of {Cu4Ln2} (Ln = Gd, Tb and Dy) complexes bearing the gem-diol form of di-2-pyridyl ketone [(py)2CO] ligand is reported. Magnetic studies reveal the presence of predominant ferromagnetic exchange interactions between the metal ions. As a result, the hexanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present. [ABSTRACT FROM AUTHOR]

A family of nanosized {Cu6Ln12} clusters with a ‘windmill’-like topology was prepared from the employment of 2,6-diacetylpyridine dioxime, in conjunction with bridging N3−, in 3d/4f-metal chemistry; the octadecanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present. [ABSTRACT FROM AUTHOR]

A pair of related dinuclear lanthanide compounds, viz., [Dy(tmhd)3]2(bptz) (1) and {Cp2Co}{[Dy(tmhd)3]2(bptz)} (2) (tmhd = 2,2,6,6-tetramethyl-3,5-heptane dionate; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) are reported. These molecules represent the first study of rare earth ions in which an organic ligand bridged species is isolated in both the neutral and radical anion forms. Both compounds exhibit out-of-phase signals below 4 K. The radical compound is highly air stable, with minimal changes in magnetic behavior after exposure to the atmosphere for two weeks. [ABSTRACT FROM AUTHOR]

A family of interwoven molecular inorganic knots, shaped like the ‘Star of David’, was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion. [ABSTRACT FROM AUTHOR]

The targeted replacement of acetate groups in the optically inactive [MnIII3O(O2CMe)3(mpko)3](ClO4) single-molecule magnet with their naphthalene, anthracene, and pyrene fluorescent analogues has led to three new emissive SMMs with enhanced photo-luminescence properties and potential applications in the field of molecular electronics. [ABSTRACT FROM AUTHOR]

The combined use of 2-(2-pyridyl)-1,3-propane-diol (pypdH 2 ) and 2-hydroxymethyl-2-(2-pyridyl)-1,3-propane-diol (pyptH 3 ) in Cu 2+ /4f chemistry has afforded a new family of isostructural [Cu 6 M 4 (pypt) 4 (pypdH) 4 (NO 3 ) 8 ] [M = Gd (1), Tb (2), Dy (3), and Y (4)] complexes. These compounds are based on an unprecedented three-layered symmetric [Cu 6 M 4 (μ-OR) 16 ] 8+ structural core, formed from the connection of the metal ions by bridging alkoxide arms of the organic ligands. Direct current magnetic susceptibility studies for complexes 1-3 revealed the presence of dominant ferromagnetic exchange interactions, suggesting the existence of large spin ground state values. Alternating current magnetic studies indicate the presence of slow-magnetic relaxation in 1-3.

The first use of the organic chelate N -hydroxy-1,8-naphthalimide (hynadH) in Dy III chemistry has unveiled access to a synthetic 'playground' composed of four new dinuclear complexes, all of which possess the same planar {Dy 2 (μ-OR) 2 } 4+ diamond-shaped core, resulting from the bridging and chelating capacity of the hynad - groups. The structural stability of the central {Dy 2 } core has allowed for the modulation of the peripheral coordination sites of the metal ions, and specifically the NO 3 - /hynad - ratio of capping groups, thus affording the compounds [Dy 2 (hynad) 2 (NO 3 ) 4 (DMF) 2 ] (1), (Me 4 N) 2 [Dy 2 (hynad) 2 (NO 3 ) 6 ] (2), [Dy 2 (hynad) 4 (NO 3 ) 2 (H 2 O) 2 ] (3), and [Dy 2 (hynad) 6 (H 2 O) 2 ] (4). Because of the chemical and structural modifications in the series 1-4, the Dy III coordination polyhedra are also dissimilar, comprising the muffin (1 and 3), tetradecahedral (2), and spherical tricapped trigonal prismatic (4) geometries. Complexes 1, 2, and 4 exhibit a ferromagnetic response at low temperatures, while 3 is antiferromagnetically coupled. All compounds exhibit out-of-phase ( χ '' M ) ac signals as a function of ac frequency and temperature, thus behaving as single-molecule magnets (SMMs), in the absence or presence of applied dc fields. Interestingly, the hynad - -rich and nitrato-free complex 4, demonstrates the largest energy barrier ( U eff = 69.62(1) K) for the magnetization reversal which is attributed to the presence of the two axial triangular faces of the spherical tricapped trigonal prism by the negatively charged O-atoms of the hynad - ligands.

The synthesis, crystal structures, Mössbauer spectra and variable temperature dc and ac magnetic susceptibility studies of a new family of trinuclear heterometallic Fe 3+ /Ln 3+ complexes, [Fe 2 Ln(PhCO 2 ) 3 ((py) 2 CO 2 )((py) 2 C(OMe)O) 2 (NO 3 )Cl] (Ln = Gd (1/Gd), Tb (1/Tb), Dy (1/Dy), and Ho (1/Ho)), where (py) 2 CO 2 2- and (py) 2 C(OMe)O - are the anions of the gem -diol and hemiketal derivatives of di-2-pyridyl ketone, are reported. Compounds 1/Ln are based on an asymmetric "V-shaped" [Fe 3+ (μ-OR)Ln(μ-OR) 2 Fe 3+ ] 6+ structural core formed from the connection of the two terminal Fe 3+ centers to the central Ln 3+ ion either through one or two alkoxide groups originating from the alkoxide-type bridging ligands. Direct current magnetic susceptibility studies reveal the presence of weak antiferromagnetic interactions between the Fe 3+ ions. Alternating current magnetic studies indicate the presence of a slow-magnetic relaxation process in 1/Dy with an energy barrier U eff = 6.7 (±0.3) K and a pre-exponential factor, τ 0 = 2.2 (±0.4) × 10 -7 s. The electronic, magnetic and relaxation properties of the complexes were further monitored by variable temperature 57 Fe Mössbauer spectroscopy. At T > 80 K the spectra from the complexes comprise two quadrupole doublets the hyperfine parameters of which reflect the distinct coordination environment of the two Fe 3+ terminal sites. At T < 20 K, the Mössbauer spectra for 1/Dy are affected by magnetic relaxation effects. At 1.5 K, the spectrum of 1/Dy comprises well defined magnetic sextets indicating relaxation times slower than the characteristic time of the Mössbauer technique (10 -7 s) in agreement with the dynamic magnetic measurements. 1/Gd exhibits broad unresolved magnetic sextets at 1.5 K indicating that the spin relaxation time is of the order of the Mössbauer characteristic time at this temperature. For 1/Tb, 1/Ho the Mössbauer spectra exhibit slight broadening even at the lowest available temperature consistent with magnetic relaxation times less than 10 -7 s.

Self-assembly reactions of CoII ions in the presence of the 2,2-bipyrimidine (bpym) ligand produced both a dinuclear and an octanuclear cation with the nuclearity being governed by hydrogen-bonding versus anion-π interactions between the anions and the ligands.

The synthesis of a new family of ferromagnetically-coupled {Ni 10 } clusters counterbalanced by various [Ln(NO 3 ) 5 ] 2- ions is herein described. The resulting compounds are organic chelate-free and the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology reminiscent of the structure of the brucite mineral.

A new family of {Cu4Ln2} (Ln = Gd, Tb and Dy) complexes bearing the gem-diol form of di-2-pyridyl ketone [(py)2CO] ligand is reported. Magnetic studies reveal the presence of predominant ferromagnetic exchange interactions between the metal ions. As a result, the hexanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

A family of nanosized {Cu 6 Ln 12 } clusters with a 'windmill'-like topology was prepared from the employment of 2,6-diacetylpyridine dioxime, in conjunction with bridging N 3 - , in 3d/4f-metal chemistry; the octadecanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

The targeted replacement of acetate groups in the optically inactive [Mn(III)3O(O2CMe)3(mpko)3](ClO4) single-molecule magnet with their naphthalene, anthracene, and pyrene fluorescent analogues has led to three new emissive SMMs with enhanced photoluminescence properties and potential applications in the field of molecular electronics.

A Mn(III)(4)Ni(II)(4) molecular square exhibiting slow magnetization relaxation has been prepared from the reaction of a Mn(II)(4)Mn(III)(6)Mn(IV)(2) cluster and a simple Ni(II) source., (This journal is © The Royal Society of Chemistry 2012)