[(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.

A series of isomorphous [M-2(ip)(2)(L)(2)](n) (M = Co, Ni; ip = isophthalate; L = 4,4'-dipyridyl and pyrazine) coordination polymers was synthesized via in situ ligand transformation reactions, in which 1,2,3-benzene tricarboxylic acid (1,2,3-btcH(3)) undergoes decarboxylation to isophthalate (ip), which was found to be highly dependent on the reaction temperature. The polymers crystallize in the same crystal triclinic system P (1) over bar. The magnetic properties were investigated by a Quantum Design physical property measurement system (PPMS); all four compounds feature almost isostructural M(II) dimers having ferromagnetic (FM) interactions. The interdimer interactions mediated by two different carboxylate groups of ip are weak, while there is no significant magnetic exchange via the 4,4'-dipyridyl ligands along the chain direction. However, substitution with pyrazine leads to antiferromagnetic exchange of nearest neighbor dimers.

A 3D metal-organic framework, [Na{Mn(3)(Hbtc)(2)(btc)}.5H(2)O](n) () (H(3)btc = 1,3,5-benzene tricarboxylic acid), was synthesized under hydrothermal conditions. The structure of was established by single crystal X-ray diffraction analysis; crystallizes in the monoclinic space group P2/c, a = 9.753(3) A, b = 12.751(2) A, c = 14.174(4) A, beta = 109.41(1) degrees . The complex is isostructural to previously reported MIL-45 and consists of one dimensional wave like chains of carboxylate bridged hexa-coordinated Mn(ii) ions. Variable temperature magnetic susceptibility measurements revealed dominant antiferromagnetic exchange interactions and the intra-chain exchange constants J(1) = -2.4 cm(-1) and J(2) = -0.6 cm(-1) compare well with literature values for similar materials. Inter-chain interactions are expected to be very small in this compound and there is no indication of magnetic ordering phenomena in the temperature range from 300-2 K.

An unprecedented architecture comprising of three isolated coordination polymers within the same crystalline structure has been obtained, in which two independent infinite one dimensional polymer chains, Cu(bpy)(H2O), fill the voids generated by a third, two dimensional, host framework, Cu3(Hbtc)(btc)(bpy)2.

Seven new di-, tri-, tetra-, and hexanuclear iron complexes that incorporate a polydentate Schiff base and variously substituted catecholate ligands have been synthesized from the trinuclear precursor [Fe(3)(OAc)(3)(L)(3)] (1), where LH(2) = 2-[[(2-hydroxyethyl)imino]phenylmethyl]-phenol. These were isolated as the compounds [Fe(3)(OAc)(Cat)(L)(3)] (2), [Fe(6)(OAc)(2)(Cat)(4)(L)(4)] (3), [Fe(4)(3,5-DBCat)(2)(L)(4)] (4), [Bu(4)N][Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)] (5a, 5(-) is the complex monoanion [Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)](-)), [Fe(4)(OAc)(3,5-DBCat)(3)(3,5-DBSQ)(L)(2)] (6), [Fe(2)(Cl(4)Cat)(2)(L)(LH(2))(H(2)O)] (7), and [Et(3)NH](2)[Fe(2)(Cl(4)Cat)(2)(L)(2)] (8a, 8(2-) is the complex dianion [Fe(2)(Cl(4)Cat)(2)(L)(2)](2-)), where CatH(2) = catechol; 3,5-DBCatH(2) = 3,5-di-tert-butyl-catechol; 3,5-DBSQH = 3,5-di-tert-butyl-semiquinone, and Cl(4)CatH(2) = tetrachlorocatechol. While compounds 2-4, 5a, 7, and 8a were obtained by directly treating 1 with the appropriate catechol, compound 6 was synthesized by chemical oxidation of 5a. These compounds have been characterized by single crystal X-ray diffraction, infrared and UV-visible spectroscopy, voltammetry, UV-visible spectroelectrochemistry, and magnetic susceptibility and magnetization measurements. An electrochemical study of the three tetranuclear complexes (4, 5(-), and 6) reveals multiple reversible redox processes due to the o-dioxolene ligands, in addition to reductive processes corresponding to the reduction of the iron(III) centers to iron(II). A voltammetric study of the progress of the chemical oxidation of compound 5a, together with a spectroelectrochemical study of the analogous electrochemical oxidation, indicates that there are two isomeric forms of the one-electron oxidized product. A relatively short-lived neutral species (5) that possesses the same ligand arrangement as complex 5(-) is the kinetic product of both chemical and electrochemical oxidation. After several hours, this species undergoes a significant structural rearrangement to convert to complex 6, which appears to be largely driven by the preference for the 3,5-DBSQ(-) ligand to bind in a non-bridging mode. Variable temperature magnetic susceptibility measurements for compounds 3, 4, 5a, 6, 7, and 8a reveal behavior dominated by pairwise antiferromagnetic exchange interactions, giving rise to a poorly isolated S = 0 ground state spin for compound 3, well-isolated S = 0 ground state spins for complexes 4, 5(-), 7 and 8(2-), and a well-isolated S = 1/2 ground state spin for complex 6. The ground state spin values were confirmed by low temperature variable field magnetization measurements. The thermal variation of the magnetic susceptibility for compounds 3, 4, 5a, 6, 7, and 8a were fitted and/or simulated using the appropriate Hamiltonians to derive J values that are consistent with magnetostructural correlations that have been reported previously for alkoxo-bridged ferric complexes.

We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]}(2)] (in which R=nPr 1, Et 2, nBu 3), [{Et(2)NH}(2){[Et(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)][HO(2)CCMe(3)](2)}(2)] (4), [{[Me(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]2.5 H(2)O}(4)] (5) and [{[iPr(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)]}(2)] (6). The structures all contain horseshoes of chromium centres, with each Cr...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 tetra-horseshoe 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 J(B) 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=-1.18 meV. The single-ion anisotropy parameters for Cr(III) were also derived for the two compounds as: for 1, D(Cr)=-0.028 meV and |E(Cr)|=0.005 meV; for 6, D(Cr)=-0.031 meV. Magnetic-field-dependent inelastic neutron scattering experiments on 1 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 +0.12 meV. 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.

Folding under pressure: High-pressure crystallography of an Mn6 single-molecule magnet reveals dramatic changes in the intramolecular geometry of the magnetic core (see picture; Mn purple, O red, N blue). These structural changes effect the magnetic properties of the molecule: the magnitude of the ferromagnetic exchange between the metals is decreased, and under extreme pressure switches to antiferromagnetic.

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.

The Q dependence of the inelastic neutron scattering (INS) intensity of transitions within the ground-state spin multiplet of single-molecule magnets 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 Mn-12 as an example. The Q dependence is calculated for powder as well as single-crystal Mn-12 samples for various exchange-coupling situations discussed in the literature. The results are compared to literature data on a powder sample of Mn-12 and to measurements on an oriented array of about 500 single crystals of Mn-12. 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 reach of today's instruments.

The syntheses of two new polynuclear TbIII compounds are reported. A tetranuclear complex [Tb4(H2L)2(H4L)2(OAc)8] (1), with H4L=2-((2-hydroxy-benzylidene)-amino)-2-hydroxy-methyl-propane-1,3-diol, has a butterfly-type structure, while [Tb(OAc)3MeOH]∞ (2) is a linear chain. A novel binding mode for H2L2− is observed in 1, with two alkoxides each bridging three TbIII ions. The magnetic properties of 1 are determined by the superposition of the ligand field split 7F6 states of TbIII single-ions located on two crystallographically distinct sites. Weak antiferromagnetic exchange interactions possibly contribute to the lowering of the magnetic moment at the lowest temperatures.

Quantum tunneling of magnetization under static and pulse magnetic fields in a Mn7 wheel-shaped single-molecule magnet has been investigated. In their Full Paper on page 8445 ff., H. Oshio et al. present their latest result in this exciting field of nano-sized magnetic materials. Gas Sensors In his Concept article on page 8376 ff., M. Tiemann discusses how mesoporosity plays a vital role in the application of semiconducting metal oxides as gas sensors. Apart from exhibiting high sensitivities, due to large specific surface areas, sensors with well-defined porosity offer powerful opportunities with respect to selectivity, self-diagnosis, low operation temperatures or long-term stability.1 π-Radical Ligands Unlike the metal-centered oxidation, which produces the nice rusty surface on a steel mill's recuperator in the background, coordination compounds like the ones from R. Holm's group shown here undergo ligand-centered oxidation. The iron ions formally possess oxidation states of +III (top), +IV (middle), and +V (bottom), but the last two do not adopt a high valent d4 and d3 electronic configuration. This topic is discussed in more detail by K. Wieghardt, F. Neese et al. in their Full Paper on page 8390 ff.1 Molecular Springs In their Full Paper on page 8454 ff., I. Huc et al. describe how enlarging the diameter of a helically folded aromatic amide oligomer by using a 1,8-diazaanthracene monomer instead of pyridine unit results in a spectacular enhancement of its ability to form a double helical hybrid. The hybridization process implies a spring-like extension of the helically folded strands to double their pitch.1

The reaction of N-(2-hydroxy-5-nitrobenzyl)iminodiethanol (=H-3(5-NO2-hbide)) with Mn(OAc)(2)center dot 4H(2)O in methanol, followed by recrystallization from 1,2-dichloroethane, yielded a wheel-shaped single-molecule magnet (SMM) of [(Mn3Mn4III)-Mn-II(5-NO2-hbide)(6)]center dot 5C(2)H(4)Cl(2) (1). In 1, seven manganese ions are linked by six tri-anionic ligands and form the wheel in which the two manganese ions on the rim and the one in the center are Mn-II and the other four manganese ions are Mn-III ions. Powder magnetic susceptibility measurements showed a gradual increase with chi T-m values as the temperature was lowered, reaching a maximum value of 53.9 emu mol(-1)K. Analyses of magnetic susceptibility data suggested a spin ground state of S=19/2. The zero-field splitting parameters of D and B-4(0) were estimated to be -0.283(1)K and -1.64(1) x 10(-5) K, respectively, by high-field EPR measurements (HF-EPR). The anisotropic parameters agreed with those estimated from magnetization and inelastic neutron scattering experiments. AC magnetic susceptibility measurements showed frequency-dependent in- and out-of-phase signals, characteristic data for an SMM, and an Arrhenius plot of the relaxation time gave a re-orientation energy barrier (Delta E) of 18.1 K and a pre-exponential factor of 1.63 x 10(-7) s. Magnetization experiments on aligned single crystals below 0.7 K showed a stepped hysteresis loop, confirming the occurrence of quantum tunneling of the on magnetization (QTM). QTM was, on the other hand, suppressed by rapid sweeps of the magnetic field even at 0.5 K. The sweep-rate dependence of the spin flips can be understood by considering the Landau-Zener-Stuckelberg (LZS) model.

Nuclear and magnetic structures of sodium ruthenate (VI) have been studied by neutron powder diffraction in the temperature range 1.5–200 K. Na2RuO4 crystallizes in the monoclinic structure, with space group P 21/c. The structure consists of apical corner sharing RuO5 trigonal bipyramids forming infinite chains running along the b axis. These infinite [ RuO3O2/2] chains form a pseudo hexagonal close packing of rods with Ru–Ru distances of 3.51 Å within the chains and 5.30–5.47 Å between the chains. At TN=37.2 K a magnetic transition leads to an antiferromagnetic state. The Ru6+ magnetic moments are ordered antiferromagnetically along the chains (b-axis), while the inter-chain interaction is ferromagnetic. A classical infinite chain model was fitted to the magnetic susceptibility data in order to estimate the strength of the nearest-neighbor exchange interactions along and between the chains, resulting in an intrachain coupling parameter of 2J=-86 K, and an interchain parameter J⊥ with \(\vert \)2J⊥ \(\vert \) = 3 K.

Reactions between Co(OAc)(2) and 2-amino-2-methyl-1,3-propanediol (ampdH(2)) afford a hexanuclear complex [Co-6(H2O)(MeOH)(OAc)(6)(ampd)(4)] (1) and a one-dimensional coordination polymer comprised of discrete heptanuclear complexes covalently bound to mononuclear Co centers [Co-8(H2O)(2)(OAc)(7)(ampd)(6)](n) (2). While 1 is obtained under ambient reaction conditions, the formation of 2 requires solvothermal methods. Both products have been characterized crystallographically and found to be mixed-valent, containing divalent and trivalent Co centers. Down to 30 K, the variable-temperature magnetic susceptibility data of 1 and 2 are dominated by the single-ion properties of highspin Co-II centers with distorted-octahedral coordination geometries. Below this temperature, the effect of intramolecular ferromagnetic exchange interactions becomes apparent. The ferromagnetic coupling in 1 has been analyzed in terms of an anisotropic exchange model, and inelastic neutron scattering data are consistent with the proposed model. Although the structure of 2 precludes a quantitative interpretation, the magnetic data suggest ferromagnetic exchange within the heptanuclear unit and negligible interactions along the chain between the hepta- and mononuclear fragments.

The synthesis and crystal structures of a family of decametallic Cr(III) "molecular wheels" are reported, namely [Cr10(OR)20(O2CR')10] [R' = Me, R = Me (1), Et (2); R' = Et, R = Me (3), Et (4); R' = CMe3, R = Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R') the nearest neighbour CrCr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R = Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S = 0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S = 15 ground state expected for ferromagnetic coupling of ten Cr(III) ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J = 0, hence changing the sign of J.

Na(10)Co(4)O(10) was investigated by neutron powder diffraction at 230, 70, and 4 K. The crystal structure, determined previously by X-ray diffraction on single crystals, was confirmed. Na(10)Co(4)O(10) orders magnetically below 37 K. All observed magnetic reflections could be indexed by integers (hkl) with respect to the chemical unit cell and the magnetic propagation vector q=0. The refinement was performed in the Shubnikov space group C2/c and indicated a collinear antiferromagnetic spin structure. The determined spin arrangement is consistent with the magnetic intratetramer interactions suggested previously from the analysis of magnetic susceptibility data: the magnetic moments of the central Co(III) ions of the Co(4)O(10) tetramer lie parallel to each other and couple in an antiparallel fashion to the terminal Co(II) moments. The Rietveld analysis shows that the net moments of 0.64 mu(B) per tetramer form ferromagnetic layers parallel to the ab plane. Adjacent layers are coupled antiferromagnetically along c. The spins are aligned in the ac plane along the line connecting adjacent Co(II) and Co(III) ions of the tetramer. We have determined unusually low values for the ordered magnetic moments of 2.43(5) mu(B) and 2.11(6) mu(B) for Co(III) and Co(II), respectively. The occurrence of spontaneous magnetization below 37 K indicates a slight canting of 2.2 degrees of the antiferromagnetic structure. A representation analysis shows that a weak ferromagnetic component along b is compatible with the determined antiferromagnetic structure.

The reaction of Ni(OAc)2, NiX2 (X=Cl, Br) or CoCl2 with the proligand 2-amino-2-methyl-1,3-propanediol (ampdH2) affords a new family of tetranuclear complexes. The syntheses of [Ni4(OAc)4(ampdH)4] (1) and [M4X4(ampdH)4] (M=Ni, X=Cl, 2; M=Ni, X=Br, 3; M=Co, X=Cl, 4) are reported, together with the single crystal X-ray structures of 1, 2 and 4 and the magnetochemical characterization of 1, 3 and 4. Each member of this family of complexes displays a low symmetry structure that incorporates a {M4O4} core unit based on a distorted cubane. Magnetic measurements reveal ferromagnetic exchange interactions for 1, 3 and 4. These give rise to S=4 ground state spins for the tetranuclear Ni complexes and an anisotropic effective S′=2 ground state for the Co complex.

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 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).