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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.

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.

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.

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.

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.

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)