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The density functional theory calculations were used to explore the S=11 ground states of the [Mn.sup.7] family of mixed-valence complexes with a metal-centered hexagonal topology. The topology was observed to arise by spin frustration involving small differences in the magnitudes of the two weakest interactions controlling the alignment of the central spin which lead to formation of complex with maximum S = 16 ground state.

Various studies are conducted to describe the properties of single-molecule magnetism (SMM) in triangular manganese(III) complexes. The results show that structural distortions of a magnetic core induced by ligands can easily 'switch on' the properties of SMM.

The distortion imposed on a [Mn3O](super 7+) member of the venerable class of triangular, oxide, centered [M3O](super 6+,7+) complexes by a tridentate oximate ligand switches the exchange coupling to ferromagnetic and makes [Mn(super III)3O](super 7+) the initial example of a triangular single-molecule magnet (SMM). This suggests that it may also be possible to modify other triangular structures with chelating and/or bridging ligands to switch on the properties of a SMM.

Energy splittings resulting from anisotropy and exchange interactions in the dimer of single-molecule magnets [Mn4O3Cl4(O2CEt)2(py)3]2.8MeCN are determined for both an undeuterated and a partially deuterated sample using inelastic neutron scattering. The antiferromagnetic (AF) exchange coupling between the two Mn4 subunits strongly depends on their separation.

The reaction between oxide-centered, triangular [MnIII3O(O2CR)6(py)3](ClO4) (R = Me (1), Et (2), Ph (3)) compounds and methyl 2-pyridyl ketone oxime (mpkoH) affords a new family of Mn/carboxylato/oximato complexes, [MnIII3O(O2CR)3(mpko)3](ClO4) [R = Me (4), Et (5), and Ph (6)]. As in 1-3, the cations of 4-6 contain an [MnII3(μ3-O)]7+ triangular core, but with each Mn2 edge now bridged by an η¹/η¹:μ-RCO2- and an η¹:η¹:η¹:μ-mpko- group. The tridentate binding mode of the latter causes a buckling of the formerly planar [MnIII3(μ3-O)]7+ core, resulting in a relative twisting of the three MnIII octahedra and the central O2- ion now lying ~0.3 Å above the Mn3 plane. This structural distortion leads to ferromagnetic exchange interactions within the molecule and a resulting S = 6 ground state. Fits of dc magnetization data for 4-6 collected in the 1.8-10.0 K and 10-70 kG ranges confirmed S= 6 ground states, and gave the following 0 and g values: -0.34 cm-1 and 1.92 for 4, -0.34 cm-1 and 1.93 for 5, and -0.35 cm-1 and 1.99 for 6, where 0 is the axial zero-field splitting (anisotropy) parameter. Complexes 4-6 all exhibit frequency-dependent out-of-phase (χ′M ac susceptibility signals suggesting them possibly to be single-molecule magnets (SMMs). Relaxation rate vs T data for complex 4 down to 1.8 K obtained from the χ′M vs T studies were supplemented with rate vs T data measured to 0.04 K via magnetization vs time decay studies, and these were used to construct Arrhenius plots from which was obtained the effective barrier to relaxation (Ueff) of 10.9 K. Magnetization vs dc field sweeps on single-crystals of 4·3CH2Cl2 displayed hysteresis loops exhibiting steps due to quantum tunneling of magnetization (QTM). The loops were essentially temperature-independent below ~0.3 K, indicating only ground-state QTM between the lowest- lying Ms = ±6 levels. Complexes 4-6 are thus confirmed as the first triangular SMMs. High-frequency EPR spectra of single crystals of 4·3CH2Cl2 have provided precise spin Hamiltonian parameters, giving 0 = -0.3 cm-1, B40 = -3 · 10-5 cm-1, and g = 2.00. The spectra also suggest a significant transverse anisotropy of E ≥ 0.015 cm-1. The combined work demonstrates the feasibility that structural distortions of a magnetic core imposed by peripheral ligands can "switch on" the properties of an SMM. [ABSTRACT FROM AUTHOR]

Abstract: The use of 2-pyridyl oximes (L’H) in reactions with has led to complexes . Ferromagnetic exchange interactions between the three MnIII ions in the complexes lead to spin ground states of S =6. The complexes display the temperature- and scan rate-dependent hysteresis loops that are indicative of single-molecule magnetism behaviour. [Copyright &y& Elsevier]

Energy splittings resulting from anisotropy and exchange interactions in the dimer of single-molecule magnets [Mn4O3Cl4(O2CEt)3(py)3]2•8MeCN are determined for both an undeuterated and a partially deuterated sample using inelastic neutron scattering. The antiferromagnetic (AF) exchange coupling between the two Mn4 aubunits strongly depends on their separation. The Cl•••Cl distance between the two subunits can be modified either by exchanging the solvent of crystallization or by deuteration of the C-H•••Cl hydrogen bonds, The exchange of acetonitrile for n-hexane leads to a five times greater shortening of the CI•••Cl separation than does full deuteration of all the hydrogen bonds. As a result, the AF exchange coupling constants between the subunits are 0.0073(4) and 0.0103-(9) meV in the samples with acetonitrile and n-hexane solvent molecules, respectively, in the crystal structure. On the other hand, the effect of C-H•••Cl deuteration on the AF exchange coupling is not detectable within the experimental accuracy of INS. [ABSTRACT FROM AUTHOR]

The use of both azide and triethanolamine, with or without the presence of carboxylate groups, has provided new Mn17, Mn18and {Mn62}ncomplexes with aesthetically-pleasing cage, layered, and linked-chain-type structures; two are also new single-molecule magnets. [ABSTRACT FROM AUTHOR]

This article focuses on a study related to single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex. Single-molecule magnets are individual molecules that function as nanoscale magnetic particles. They derive their properties from the combination of a large ground-state spin and a magnetoanisotropy of the king-type. An ideal material for a white-light emitting intrinsic layer would be robust, emit over the entire visible spectrum, have high quantum efficiency, not suffer from self absorption, be easy to produce on a large scale, and not waste energy producing wavelengths beyond the visible spectrum.

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [Fe 7 O 3 (O 2 CPh) 9 (mda) 3 (H 2 O)] ( 1 ), [Fe 22 O 14 (OH) 3 (O 2 CMe) 21 (mda) 6 ](ClO 4 ) 2 ( 2 ), and [Fe 24 O 15 (OH) 4 (OEt)(O 2 CMe) 21 (mda) 7 ](ClO 4 ) 2 ( 3 ), where mdaH 2 is N -methyldiethanolamine. 1 was prepared from the reaction of [Fe 3 O(O 2 CPh) 6 (H 2 O) 3 ](NO 3 ) with mdaH 2 in a 1:2 ratio in MeCN, whereas 2 and 3 were prepared from the reaction of FeCl 3 /NaO 2 CMe/mdaH 2 in a 2:∼13:2 ratio and FeCl 3 /NaO 2 CMe/mdaH 2 /pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of 1 consists of a central octahedral Fe III ion held within a nonplanar Fe 6 loop by three μ 3 -O 2- and three μ 2 -RO - arms from the three mda 2- chelates. The cores of the cations of 2 and 3 consist of an A : B : A three-layer topology, in which a central Fe 6 ( 2 ) or Fe 8 ( 3 ) layer B is sandwiched between two Fe 8 layers A . The A layers structurally resemble 1 with the additional Fe added at the center to retain virtual C 3 symmetry. The central Fe 6 layer B of 2 consists of a {Fe 4 (μ 4 -O) 2 (μ 3 -OH) 2 } 6+ cubane with an Fe on either side attached to cubane O 2- ions, whereas that of 3 has the same cubane but with an {Fe 3 (μ 3 -O)(μ-OH)} unit attached on one side and a single Fe on the other. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling in all complexes leading to ground-state spins of S = 5 / 2 for 1 and S = 0 for 2 and 3 . All Fe 2 pairwise exchange parameters ( J ij ) for 1 - 3 were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity Fe III /O complexes. The two approaches gave satisfyingly similar J ij values, and the latter allowed rationalization of the experimental ground states by identification of the spin frustration effects operative and the resultant relative spin vector alignments at each Fe III ion.

The use of both azide and triethanolamine, with or without the presence of carboxylate groups, has provided new Mn(17), Mn(18) and {Mn(62)}(n) complexes with aesthetically-pleasing cage, layered, and linked-chain-type structures; two are also new single-molecule magnets.