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We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R2NH2](3) [Cr6F11 (O2CCMe3)(10)]}(2)] (in which R=nPr 1, Et 2, nBu 3), [{Et2NH}(2) {[Et2NH2](3)[Cr7F12(O2C-CMe3)(12)][HO2CCMe3](2)}(2)] (4), [{[Me2NH2](3)[Cr6F11(O2CCMe3)(10)]center dot 2.5 H2O}(4)] (5) and [I{iPr(2)NH(2)](3)[Cr7F12(O2CCMe3)(12)]}(2)] (6). The structures all contain horseshoes of chromium centres, with each Cr center dot center dot center dot Cr contact within the horseshoe bridged by a fluoride and two pivalates. The horseshoes are linked through hydrogen bonds to the secondary ammonium cations in the structure, leading to di- and tetrahorseshoe structures. Through magnetic measurements and inelastic neutron scattering studies we have determined the exchange coupling constants in 1 and 6. In 1 it is possible to distinguish two exchange interactions, J(A) = -1.1 meV and J(B) = -1.4 meV; J(A) is the exchange interactions at the tips of the horseshoe and JB is the exchange within the body of the horseshoe (1 meV = 8.066 cm(-1)). For 6 only one interaction was needed to model the data: J=-1.18meV The single-ion anisotropy parameters for Cr-III were also derived for the two compounds as: for 1, D-Cr = -0.028 meV and vertical bar ECr vertical bar = 0.005meV; for 6, D-Cr=-0.031meV. Magnetic-field-dependent inelastic neutron scattering experiments on I allowed the Zeeman splitting of the first two excited states and level crossings to be observed. For the tetramer of horseshoes (5), quantum Monte Carlo calculations were used to fit the magnetic susceptibility behaviour, giving two exchange interactions within the horseshoe (-1.32 and -1.65 meV) and a weak inter-horseshoe coupling of +0.12meV. Multi-frequency variable-temperature EPR studies on 1, 2 and 6 have also been performed, allowing further characterisation of the spin Hamiltonian parameters of these chains.

We feature our recent work in the field of single-molecule magnets (SMMs) using inelastic neutron scattering (INS). The term "pressure" in the title has a triple meaning. First, there is the expectation from research-funding agencies and the public to make some significant steps towards applications. Second, the synthesis of new compounds and the applications of physical techniques for their understanding are being pushed to their limits. And third, by applying hydrostatic pressure, valuable insight into the mechanisms behind the SMM phenomena can be gained. Examples from our research have been taken to illustrate these points. After a brief introduction to the technique, the strength of INS for the accurate determination of exchange and anisotropy interactions in SMMs is highlighted. We hope to demonstrate that, by pushing INS measurements to their limits, i.e., using the best available neutron sources and instrumentation, combined with high quality samples, new insights into the relevant physical processes in SMMs can be gained.

A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.

A series of bimetallic, trigonal bipyramidal clusters of type {[Co(N-N)(2)](3)[Fe(CN)(6)](2)} are reported. The reaction of {Co(tmphen)(2)}(2+) with [Fe(CN)(6)](3)(-) in MeCN affords {[Co(tmphen)(2)](3)[Fe(CN)(6)](2)} (1). The cluster can exist in three different solid-state phases: a red crystalline phase, a blue solid phase obtained by exposure of the red crystals to moisture, and a red solid phase obtained by desolvation of the blue solid phase in vacuo. The properties of cluster 1 are extremely sensitive to both temperature and solvent content in each of these phases. Variable-temperature X-ray crystallography; (57)Fe Mossbauer, vibrational, and optical spectroscopies; and magnetochemical studies were used to study the three phases of 1 and related compounds, Na{[Co(tmphen)(2)](3)[Fe(CN)(6)](2)}(ClO(4))(2) (2), {[Co(bpy)(2)](3)[Fe(CN)(6)](2)}[Fe(CN)(6)](1/3) (3), and {[Ni(tmphen)(2)](3)[Fe(CN)(6)](2)} (4). The combined structural and spectroscopic investigation of 1-4 leads to the unambiguous conclusion that 1 can exist in different electronic isomeric forms, {Co(III)(2)Co(II)Fe(II)(2)} (1A), {Co(III)Co(II)(2)Fe(III)Fe(II)} (1B), and {Co(II)(3)Fe(III)(2)} (1C), and that it can undergo a charge-transfer-induced spin transition (CTIST). This is the first time that such a phenomenon has been observed for a Co/Fe molecule.

Molecular magnets are crystalline materials made up of interacting magnetic centres within each molecule. Each such “spin-cluster” is magnetically well isolated from its neighbours due to the surrounding ligands. The resulting magnetic properties are governed by exchange interactions between neighbouring spins and magneto-crystalline anisotropy. We present a brief overview of the salient features observed in three very different molecular magnets (Mn 4 , Ni 12 and V 15 ) where magnetic frustration plays a crucial role. It is demonstrated that Inelastic Neutron Scattering (INS) is an excellent technique to elucidate complex behaviour associated with geometrically frustrated molecular magnets.

The magnetic exchange interactions in the mixed-valence dodecanuclear polyoxovanadate compounds Na-4[V(8)(IV)V(4)(V)A(8)(III)O(40)(H2O)].23H(2)O, Na-4[(V8V4As8O40)-V-IV-As-V-O-III(D2O)].16.5D(2)O, and (NHEt3)(4)[(V8V4As8O40)-V-IV-As-V-O-III(H2O)].H2O were investigated by an inelastic neutron scattering (INS) study using cold neutrons. In addition, the synthesis procedures and the single-crystal X-ray structures of these compounds have been investigated together with the temperature dependence of their magnetic susceptibilities. The magnetic properties below 100 K can be described by simply taking into account an antiferromagnetically exchange coupled tetramer, consisting of four vanadium(IV) ions. Up to four magnetic transitions between the cluster S = 0 ground state and excited states could be observed by INS. The transition energies and the relative INS intensities could be modeled on the basis of the following exchange Hamiltonian: (S) over cap (ex) = -2J(12)(xy)((S) over cap (1x)(S) over cap (2x) + (S) over cap (3x)(S) over cap (4x) + (S) over cap (1y)(S) over cap (2y) + (S) over bar (3y)(S) over bar (4y)) - 2J(12)(z)((S) over bar (1z)(S) over bar (2z) + (S) over bar (3z)(S) over bar (4z)) - 2J(23)(xy)((S) over bar (2x)(S) over bar (3x) + (S) over bar (1x)(S) over cap (4x)+ (S) over cap (2y)(S) over cap (3y)+ (S) over cap (1y)(S) over cap (4y)) - 2J(23)(z)((S) over cap (2z)(S) over cap (3z) + (S) over cap (1z)(S) over cap (4z)). The following sets of parameters were derived: for Na-4[V12As8O40(H2O)].23H(2)O, J(12)(xy) = J(12)(z) = -0.80 meV, J(23)(xy) = J(23)(z) = -0.72 meV; for Na-4[V12As8O40(D2O)].16.5D(2)O, J(12)(xy) = J(12)(z) = J(23)(xy) = J(23)(z) = -0.78 meV; for (NHEt3)(4)[V12As8O40(H2O)].H2O, J(12)(xy) = -0.80 meV, J(12)(z) = -0.82 meV, J(23)(xy) = -0.67 meV, J(23)(z) = -0.69 meV. This study of the same {V12As8}-type cluster in three different crystal environments allows us to draw some conclusions concerning the applicability on INS in the area of nondeuterated molecular spin clusters. In addition, the effects of using nondeuterated samples and different sample container shapes for INS were evaluated.

We report an Inelastic Neutron Scattering (INS) study of the fully deuterated molecular compound K6[V15As6O42].9(D2O) (V15). Due to geometrical frustration, the essential physics at low temperatures of the V15 cluster containing 15 coupled V4+ (S=1/2) is determined by three weakly coupled spin-1/2 on a triangle. The INS spectra at low-energy allow us to directly determine the effective exchange coupling J0 = 0.211 meV within the triangle and the gap 2 \Delta = 0.035(2)meV between the two spin-1/2 doublets of the ground state. Results are discussed in terms of deviations from trigonal symmetry and Dzyaloshinskii-Moriya (DM) interactions., Comment: 8 pages, 4 figures. to appear in Europhysics Letters

A theoretical concept for setting up 1D magnetic interactions between organic radicals aligned into chains within channels of inclusion compounds is presented by calculating collinear intermolecular binding energies using ab initio methods, followed by a Markov model to predict the characteristic length of chains. Experimentally, inclusion crystals providing radicals in channels of perhydrotriphenylene (PHTP) and tris(o-phenylenedioxy)cyclotriphosphazene (TPP) were obtained by co-crystallisation or in-diffusion of the 1,3,5-trithia-2,4,6-triazapentalenyl radical (TTTA).

The molecular spin cluster V15 is a polyoxovanadate with 15 spins s=1/2 but total spin ground state S=1/2 due to strong antiferromagnetic (AFM) interactions. Below 1 K, the relaxation of the magnetisation exhibits a very peculiar behaviour in connection of the multi-spin character of the cluster and the ground state is composed of two non-degenerate S=1/2 Kramers doublets separated by a gap of about 0.3 K. The mechanism leading to such gap formation in the ground state has been elucidated using inelastic neutrons scattering (INS) under magnetic field. The observation and characterisation of several field-dependent INS transitions enable a comprehensive understanding of the low-energy quantum spin states. The energy gap between the two Kramers doublets is caused by slight deviations from the trigonal symmetry (symmetry lowering) of the cluster. The INS data are successfully mapped onto an S=1/2 AFM Heisenberg triangle with scalene distortion and a quantitative description of the wavefunction mixing (entanglement) within the ground state is derived. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; [(iC3H7)2NH2][Cr8NiF9(O2CCMe)18], or Cr8Ni, is a prominent example of an odd-membered antiferromagnetic "wheel." A detailed characterization of the magnetic properties of Cr8Ni has been conducted. Inelastic neutron scattering (INS) is used to investigate the energy and momentum transfer dependence of the low-lying spin excitations, including excited states inaccessible by other experimental techniques. The richness of the INS data, in conjunction with microscopic spin Hamiltonian simulations, enables an accurate characterization of the magnetic properties of Cr8Ni. Nearest-neighbor exchange constants of JCrCr = 1.31 meV and JCrNi = 3.22 meV are determined, and clear evidence of axial single-ion anisotropy is found. The parameters determined by INS are shown to fit magnetic susceptibility. The spectroscopic identification of several successive S=1 excited total spin states and lowest spin band excitations show that the rotational band picture, valid for bipartite AFM wheels, breaks down for this odd-numbered wheel. The exchange constants determined here differ from previous efforts based on bulk measurements, and possible reasons are discussed. The large JCrNi/JCrCr ratio in Cr8Ni puts this wheel into a regime with strong quantum fluctuations in which the ground state can be described with a valence bond solid state picture.

We report on inelastic neutron scattering (INS) measurements on the molecular spin ring CsFe$_8$, in which eight spin-5/2 Fe(III) ions are coupled by nearest-neighbor antiferromagnetic Heisenberg interaction. We have recorded INS data on a non-deuterated powder sample up to high energies at the time-of-flight spectrometers FOCUS at PSI and MARI at ISIS, which clearly show the excitation of spin waves in the ring. Due to the small number of spin sites, the spin-wave dispersion relation is not continuous but quantized. Furthermore, the system exhibits a gap between the ground state and the first excited state. We have modeled our data using exact diagonalization of a Heisenberg-exchange Hamiltonian together with a small single-ion anisotropy term. Due to the molecule's symmetry, only two parameters $J$ and $D$ are needed to obtain excellent agreement with the data. The results can be well described within the framework of the rotational-band model as well as antiferromagnetic spin-wave theories., 10 pages, 9 figures, REVTEX 4

A field-dependent inelastic neutron scattering (INS) experiment on an array of oriented single crystals of Mn12-acetate is reported. The experimental results provide clear evidence that the minority species observed in the INS spectra is the fast-relaxing species observed in, for instance, AC-susceptibility measurements.

The antiferromagnetic molecular finite chain Cr6 was studied by inelastic neutron scattering. The observed magnetic excitations at 2.6 and 4.3 meV correspond, due to the open boundaries of a finite chain, to standing spin waves. The determined energy spectrum revealed an essentially classical spin structure. Hence, various spin-wave theories were investigated in order to assess their potential for describing the elementary excitations of finite spin systems., Comment: 6 pages, 6 figures, accepted for publication in Europhysics Letters

The Q dependence of the inelastic neutron scattering (INS) intensity of transitions within the ground-state spin multiplet of single-molecule magnets (SMMs) is considered. For these transitions, the Q dependence is related to the spin density map in the ground state, which in turn is governed by the Heisenberg exchange interactions in the cluster. This provides the possibility to infer the exchange-coupling constants from the Q dependence of the INS transitions within the spin ground state. The potential of this strategy is explored for the M = +-10 -> +- 9 transition within the S = 10 multiplet of the molecule Mn12 as an example. The Q dependence is calculated for powder as well as single-crystal Mn12 samples for various exchange-coupling situations discussed in the literature. The results are compared to literature data on a powder sample of Mn12 and to measurements on an oriented array of about 500 single-crystals of Mn12. The calculated Q dependence exhibits significant variation with the exchange-coupling constants, in particular for a single-crystal sample, but the experimental findings did not permit an unambiguous determination. However, although challenging, suitable experiments are within the reach of today's instruments., 11 pages, 6 figures, REVTEX4, to appear in PRB

We feature our recent work in the field of single-molecule magnets (SMMs) using inelastic neutron scattering (INS). The term "pressure" in the title has a triple meaning. First, there is the expectation from research-funding agencies and the public to make some significant steps towards applications. Second, the synthesis of new compounds and the applications of physical techniques for their understanding are being pushed to their limits. And third, by applying hydrostatic pressure, valuable insight into the mechanisms behind the SMM phenomena can be gained. Examples from our research have been taken to illustrate these points. After a brief introduction to the technique, the strength of INS for the accurate determination of exchange and anisotropy interactions in SMMs is highlighted. We hope to demonstrate that, by pushing INS measurements to their limits, i.e., using the best available neutron sources and instrumentation, combined with high quality samples, new insights into the relevant physical processes in SMMs can be gained.

The low-lying magnetic excitations in the dimers of single-molecule magnets [Mn{sub 4}O{sub 3}Cl{sub 4}(O{sub 2}CEt){sub 3}(py){sub 3}]{sub 2}, or (Mn{sub 4}){sub 2}, are studied by inelastic neutron scattering as a function of hydrostatic pressure. The anisotropy parameters D and B{sub 0}{sup 4}, which describe each Mn{sub 4} subunit, are essentially pressure independent, while the antiferromagnetic exchange coupling J between the two Mn{sub 4} subunits strongly depends on pressure, with an increase of 42% at 17 kbar. Additional pressure-dependent powder x-ray measurements allow a structural interpretation of the findings.

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 subunits 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 Cl...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.

The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties of the isosceles triangular Co(3) spin cluster is anisotropic and is expressed as H = - 2sigma(alpha)(=)(x,y,z)(J(alpha)(12)S(1alpha)S(2alpha) + J(alpha)(23)S(2alpha)S(3alpha) + J(alpha)(13)S(1alpha)S(3alpha)), where J(alpha) are the components of the exchange interactions between the Co(II) ions. To reproduce the INS data, nonparallel anisotropic exchange tensors needed to be introduced, which were directly connected to the molecular symmetry of the complex. The following range of parameters (value +/- 0.5 cm(-1)) was found to reproduce all experimental information while taking magnetostructural relations into account: J(x)(12) = J(y)(13) = 8.6 cm(-1); J(y)(12) = J(x)(13) = 1.4 cm(-1); J(z)(12) = J(z)(13) = 10.0 cm(-1); J(x)(23) = J(y)(23) = 6.5 cm(-1) and = 3.4 cm(-1).

Reactions between the complex [MnII(L)]2+, where L is a N3O2 macrocyclic ligand, and different cyanometalate precursors such as [M(CN)n]m- (M(III) = Cr, Fe; M(II) = Fe, Ni, Pd, Pt) lead to cyano-bridged molecular assemblies exhibiting a variety of structural topologies. The reaction between [MnII(L)]2+ and [FeII(CN)6]4- forms a trinuclear complex with formula [(MnII(L)(H2O))2(FeII(micro-CN)2(CN)4)] x 2MeOH x 10H2O (1) which crystallizes in the triclinic space group P1. The reaction between [MnII(L)]2+ and [M(II)(CN)4]2-, where M(II) = Ni (2), Pd (3), Pt (4), gives rise to three isostructural linear chain compounds with stoichiometry [(MnII(L))(M(II)(micro-CN)2(CN)2)]n and which crystallize in the monoclinic space group C2/c. The self-assembly between [MnII(L)]2+ with [M(III)(CN)6]3-, where M(III) = Cr (5), Fe (6, 7, 8), forms three types of compounds. Compounds 5 and 6 are isostructural (monoclinic, space group P2(1)/n), and the structures comprise anionic linear chains [(MnII(L))(M(III)(micro-CN)2(CN)4)]n(n-) with cationic trinuclear complexes [(MnII(L)(H2O))2(M(III)(micro-CN)2(CN)4)]+ as counterions. Using an excess of K3[FeIII(CN)6], an analogous compound to 6 but with K+ as counterion is obtained (7), which crystallizes in the triclinic space group P1. Compound 8 consists of 2-D layers with formula [(MnII(L))3(FeIII(micro-CN)4(CN)2)(FeIII(micro-CN)2(CN)4)]n x 2nMeOH; it crystallizes in the monoclinic space group P2(1)/n. The magnetic properties were investigated for all samples. In particular, compound 5, which shows antiferromagnetic exchange interactions between Mn(II) and Cr(III) ions through cyanide bridging ligands, has been studied in detail; the magnetic exchange parameter amounts to J = -7.5(7) cm(-1). Compound 8 shows a magnetically ordered phase below 6.4 K which is confirmed by Mössbauer spectroscopy; two hyperfine split spectra were observed below Tc from which IJI values of 2.1 and 1.6 cm(-1) could be deduced.

We report inelastic neutron scattering (INS) studies on a series of Mn(12) derivatives, [Mn(12)O(12)(O2CC6F5)16(H2O)4]z, in which the number of unpaired electrons in the cluster is varied. We investigated three oxidation levels: z = 0 for the neutral complex, z = -1 for the one-electron reduced species and z = -2 for the two-electron reduced complex. For z = 0, the ground state is S = 10 as in the prototypical Mn12-acetate. For z = -1, we have S = 19/2, and for z = - 2, an S = 10 ground state is retrieved. INS studies show that the axial zero-field splitting parameter D is strongly suppressed upon successive electron reduction: D = -0.45 cm(-1) (z = 0), D = -0.35 cm(-1) (z = -1), and D approximately -0.26 cm(-1) (z = -2). Each electron reduction step is directly correlated to the conversion of one anisotropic (Jahn-Teller distorted) Mn3+ (S = 2) to one nearly isotropic Mn2+ (S = 5/2).

A high resolution inelastic neutron scattering (INS) study of fully deuterated Mn$_{12}$-acetate provides the most accurate spin Hamiltonian parameters for this prototype single molecule magnet so far. The Mn$_{12}$-clusters deviate from axial symmetry, a non-zero rhombic term in the model Hamiltonian leading to excellent agreement with observed positions and intensities of the INS peaks. The following parameter set provides the best agreement with the experimental data: $D=-0.0570(1)$ meV, $B_{4}^0=-2.78(7)\cdot 10^{-6}$ meV, $B_{4}^4=-3.2(6)\cdot 10^{-6}$ meV and $\mid$\textit{E}$\mid =6.8(15)\cdot 10^{-4}$ meV. Crystal dislocations are not the likely cause of the symmetry lowering. Rather, this study lends strong support to a recently proposed model, which is based on the presence of several molecular isomers with distinct spin Hamiltonian parameters., 4 pages, 4 figures

The anisotropy splitting in the ground state of the single-molecule magnet ${\mathrm{Mn}}_{4}{\mathrm{O}}_{3}\mathrm{Br}{(\mathrm{O}\mathrm{Ac})}_{3}{(\mathrm{dbm})}_{3}$ is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetization relaxation at low temperatures. The value of the negative axial anisotropy parameter ${D}_{\text{cluster}}$ changes from $\ensuremath{-}0.0627(1)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at ambient to $\ensuremath{-}0.0603(3)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at $12\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from $1.260(5)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}1.213(9)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Since the $\mathrm{Mn}\mathrm{Br}$ bond is significantly softer and thus more compressible than the $\mathrm{Mn}\mathrm{O}$ bonds, pressure induces a tilt of the single ion ${\mathrm{Mn}}^{3+}$ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy.

The synthesis and structural characterisation of three small nickel(II) cages are reported, all stabilised by pivalate ligands. The magnetic properties of the cages have been studied by a combination of susceptibility measurements and inelastic neutron scattering. For a dinuclear cage, [Ni2(μ-OH2)(O2CCMe3)4(HO2CCMe3)4] 1 the ground state is S = 2, with a ferromagnetic exchange interaction between the Ni(II) centres of J = 0.32 meV and DS=2 = −0.09 meV in the ground state. For a tetranuclear heterocubane cage, [Ni4(μ3-OMe)4(O2CCMe3)4(MeOH)4] 2, two ferromagnetic exchange interactions are found and an S = 4 ground state observed. While the zero-field splitting of this state cannot be determined unambigiously the most likely value is DS=4 = −0.035 meV. For a tetranuclear nickel butterfly, [Ni4(μ3-OH)2(O2CCMe3)6(EtOH)6] 3, three exchange interactions are required, two anti-ferromagnetic and one weakly ferromagnetic; the resulting ground state is S = 0. The data enable us to estimate the zero-field splitting of single Ni(II) ions involved in the cage as Di = +1.0 meV. Both 1 and 2 are therefore expected to be new single molecule magnets.

We perform inelastic neutron scattering measurements on the molecular nanomagnet ${\mathrm{Mn}}_{12}$-acetate to measure the excitation spectrum up to $45\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ $(500\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. We isolate magnetic excitations in two groups at $5--6.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ $(60--75\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and $8--10.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ $(95--120\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, with higher levels appearing only at $27\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.2em}{0ex}}(310\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and $31\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.2em}{0ex}}(360\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. From a detailed characterization of the transition peaks we show that all of the low-energy modes appear to be separate $S=9$ excitations above the $S=10$ ground state, with the peak at $27\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.2em}{0ex}}(310\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ corresponding to the first $S=11$ excitation. We consider a general model for the four exchange interaction parameters of the molecule. The static susceptibility is computed by high-temperature series expansion and the energy spectrum, matrix elements, and ground-state spin configuration by exact diagonalization. The theoretical results are matched with experimental observation by inclusion of cluster anisotropy parameters, revealing strong constraints on possible parameter sets. We conclude that only a model with dominant exchange couplings ${J}_{1}\ensuremath{\sim}{J}_{2}\ensuremath{\sim}5.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.2em}{0ex}}(65\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and small couplings ${J}_{3}\ensuremath{\sim}{J}_{4}\ensuremath{\sim}0.6\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.3em}{0ex}}(7\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ is consistent with the experimental data.

Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. Mössbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species.

The anisotropy splitting in the ground state of the single-molecule magnet [Mn4O3Br(OAc)3(dbm)3] is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetisation relaxation at low temperatures. The value of the negative axial anisotropy parameter $D_{\rm cluster}$ changes from -0.0627(1) meV at ambient to -0.0603(3) meV at 12 kbar pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from 1.260(5) meV to 1.213(9) meV. Since the $\rm Mn-Br$ bond is significantly softer and thus more compressible than the $\rm Mn-O$ bonds, pressure induces a tilt of the single ion Mn$^{3+}$ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy., 4 pages, 3 figures

We review our recent work in the field of molecular spin clusters and single-molecule magnets, showing how inelastic neutron scattering (INS) can be used to determine magnetic exchange interactions and anisotropy splittings. A general introduction to neutron scattering precedes selected examples, building upon the first determination of exchange coupling in a transition metal complex using INS, through anisotropic exchange in cobalt(II) spin clusters to the determination of exchange interactions in a dodecanuclear nickel(II) wheel. The strength of INS for the accurate determination of anisotropy splittings in single-molecule magnets is revealed. Not only can one determine the axial zero-field splitting parameter D, which plays a key role in single-molecule magnet behavior, but also higher-order terms important in understanding the quantum tunneling behavior. Finally, we review two of our synthetic approaches towards new single-molecule magnets based on nickel, manganese, and iron.

The tetramer-based compound α-MnMoO 4 exhibits four prominent peaks in the inelastic neutron scattering (INS) spectrum between 0.5 and 2.0 meV below 10 K. They are assigned to magnetic excitations of the (Mn 2 + ) 4 rhombus shaped cluster, with resulting values of the exchange parameters J= +0.051 meV and J' = -0.019 meV along the edges and the short diagonal, respectively. The interactions within the tetramer are treated exactly in an isotropic quantum mechanical model leading to an S = 10 cluster ground state. The weaker antiferromagnetic (AFM) intercluster interactions, J i n t = -4.5×10 3 meV, are treated in a molecular-field model below the AFM transition temperature T N = 10.7 K. INS and susceptibility are in quantitative agreement with this approach.

A charge-transfer-induced spin transition (CTIST) is observed in the discrete cyanide-bridged complex, {[Co(tmphen)2]3[Fe(CN)6]2}. Single-crystal X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetic susceptibility were used collectively to describe the oxidation states of the Co and Fe ions in this cluster as a function of temperature. This pentanuclear complex represents the first example of a CTIST at the discrete molecular level.

Time-resolved inelastic neutron scattering measurements on an array of single-crystals of the single-molecule magnet Mn12ac are presented. The data facilitate a spectroscopic investigation of the slow relaxation of the magnetization in this compound in the time domain., Comment: 3 pages, 4 figures, REVTEX4, to appear in Appl. Phys. Lett., for an animation see also http://www.dcb.unibe.ch/groups/guedel/members/ow2/trins.htm

Crucial to the commercial exploitation of any service combining UMTS and DVB-T is the availability of standardised APIs adapted to the hybrid UMTS and DVB-T network and to the technical limitations of mobile/portable terminals. This paper describes work carried out in the European Commission Framework Programme 5 (FP5) project CONFLUENT to demonstrate the feasibility of such Application Programme Interfaces (APIs) by enabling the reception of a Multimedia Home Platform (MHP) based application transmitted over DVB-T on five different terminals with parts of the service running on a mobile phone.

The cover picture shows the principles of inelastic neutron scattering (INS) in magnetic molecular clusters. An incoming monochromatic neutron beam is scattered by a target sample (here a tetranuclear nickel(II) complex) both elastically (no energy transfer) and inelastically (positive or negative energy transfer). Scattered neutrons of varying velocity are then collected in detector banks that span a wide angular range. The interactions between the magnetic moments of the sample and the neutrons that occur during INS allow the investigation of the magnetic properties of the material and the accurate determination of the relevant parameters, including those associated with exchange interactions and magnetoanisotropy. This is nicely illustrated by the inelastic peaks, observed on both sides of the elastic line, which correspond to magnetic energy transfer between the neutrons and the sample. INS is a unique technique that affords a detailed insight into the magnetic levels over a large energy range (up to 1000 cm−1) and thus can provide crucial information for a wide variety of magnetic materials. For more information, see the review by Gudel and co-workers on pages 910–926.

We report an inelastic neutron scattering (INS) study under a magnetic field on the frustrated molecular spin cluster $V_{15}$. Several field-dependent transitions are observed and provide a comprehensive understanding of the low-energy quantum spin states. The energy gap $2 \Delta_{0}\approx 27(3)\mu$eV between the two lowest $S=1/2$ Kramers doublets is unambiguously attributed to a symmetry lowering of the cluster. The INS data are mapped onto an S=1/2 Antiferromagnetic Heisenberg triangle with scalene distortion. A quantitative description of the wavefunction mixing within the ground state is derived., Comment: To be published in Europhysics Letters 7 pages, 3 figures