Magnetic Properties of the Distorted Kagomé Lattice Mn3(1,2,4-(O2C)3C6H3)2.

Kagomé lattice types have been of intense interest as idealized examples of extended frustrated spin systems. Here we demonstrate how the use of neutron diffraction and inelastic neutron scattering coupled with spin wave theory calculations can be used to elucidate the complex magnetic interactions of extended spin networks. We show that the magnetic properties of the coordination polymer Mn3(1,2,4-(O2C)3C6H3)2, a highly distorted kagomé lattice, have been erroneously characterized as a canted antiferromagnet in previous works. Our results demonstrate that, although the magnetic structure is ferrimagnetic, with a net magnetic moment, frustration persists in the system. We conclude by showing that the conventions of the Goodenough-Kanamori rules, which are often applied to similar magnetic exchange interactions, are not relevant in this case.

Magnetism of linear [Ln3](9+) oxo-bridged clusters (Ln = Pr, Nd) supported inside a [R3PR'](+) phosphonium coordination material.

Two new isostructural phosphine coordination materials, Ln-PCM-21 (Ln = Pr, Nd), have been obtained using a tris(p-carboxylated) methyltriphenylphosphonium ligand that is formally dianionic when triply deprotonated, allowing access to materials based on uncommon metal-to-ligand ratios. The polymers of the formula [Ln3(mptbc)4]X·solv (X = Cl(-), NO3(-)) are cationic and contain unusual, linear oxo-bridged [Ln3](9+) clusters. Magnetic susceptibility data for both the Pr and Nd analogues has been compared to models based on three contrasting approaches.

Switchable magnetism: neutron diffraction studies of the desolvated coordination polymer Co3(OH)2(C4O4)2.

We report the magnetic structure of the two magnetically ordered phases of Co3(OH)2(C4O4)2, a coordination polymer that consists of a triangular framework decorated with anisotropic Co(II) ions. Neutron diffraction experiments allow us to confirm that the magnetic behavior changes upon dehydration and reveal the complex phase behavior of this system, relative to the hydrated compound Co3(OH)2(C4O4)2·3H2O. One phase is shown to display spin idle behavior, where only a fraction of the moments order at intermediate temperatures, while at the lowest temperatures the system orders fully, in this case with a net magnetic moment. This novel magnetic behavior is discussed within the framework of a simple Hamiltonian and representational analysis and rationalizes this multiphase behavior by considering the combination of frustration and anisotropy. The change in behavior on dehydration is also rationalized with respect to the changes in the single-ion anisotropy of the cobalt.

Formation of Ti28 ln cages, the highest nuclearity polyoxotitanates (Ln = La, Ce).

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln = La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type (see figure).

Two stage magnetic ordering and spin idle behavior of the coordination polymer Co3(OH)2(C4O4)2·3H2O determined using neutron diffraction.

We report the magnetic structure of two of the magnetically ordered phases of Co(3)(OH)(2)(C(4)O(4))(2)·3H(2)O, a coordination polymer that consists of a triangular framework decorated with anisotropic Co(II) ions. The combination of neutron diffraction experiments and magnetic susceptibility data allows us to identify one phase as displaying spin idle behavior, where only a fraction of the moments order at intermediate temperatures, while at the lowest temperatures the system orders fully. This novel magnetic behavior is discussed within the framework of a simple Hamiltonian and representational analysis and rationalizes this multiphase behavior by considering the combination of frustration and anisotropy.

A simple approach to coordination compounds of the pentacyanocyclopentadienide anion.

Deprotonation of [Et(3)NH][C(5)(CN)(5)] with metal bases provides a very simple approach to coordination compounds containing the pentacyanocyclopentadienide anion [C(5)(CN)(5)](-) (1). The three-dimensional polymer [Na(thf)(1.5)(1)](∞) and the molecular dimer [{(tmeda)(2)Na(1)}(2)] are obtained by reaction of this precursor with NaH in the presence of thf or tmeda (Me(2)NCH(2)CH(2)NMe(2)). Their single-crystal X-ray structures both reveal σ-bonded C≡N-Na arrangements and π stacking between [C(5)(CN)(5)](-) ions. DFT calculations on the [C(5)(CN)(5)](-) ion have been used to investigate the structures and bonding in [Na(thf)(1.5)(1)](∞) and [{(tmeda)(2)Na(1)}(2)]. The absence of π bonding of the metal ions in both complexes is due to dispersion of the negative charge from the C(5) ring unit to the C[triple chemical bond]N groups in the [C(5)(CN)(5)](-) ion, making the coordination chemistry of this anion distinctly different from that of cyclopentadienide C(5)H(5)(-).

Mixed alkali metal/transition metal coordination polymers with the mellitic acid hexaanion: 2-dimensional hexagonal magnetic nets.

The hexaanion of mellitic acid, mel = (C(6)(CO(2))(6))(6-), links metal ions into extensively connected magnetic coordination polymers. Reaction of alkali metal mellitate salts, M(6)(mel) (M = K, Rb), with M'Cl(2) precursors (M' = Mn, Co, Ni) under mild (473 K) hydrothermal conditions yields an extensive family of isostructural 3-dimensional mixed alkali metal/transition metal polymers of general formula M(2)[M'(2)(mel)(OH(2))(2)] (M/M' = K/Mn (1a); K/Co (1b); K/Ni (1c); Rb/Mn (2a); Rb/Co (2b); Rb/Ni (2c)). These materials incorporate distorted 2-dimensional magnetic hexagonal nets with a honeycomb topology that are exclusively based on metal-carboxylate-metal bridging interactions. A further isostructural alkali metal-free Co(2+) material with NH(4)(+) cations, (NH(4))(2)[Co(2)(mel)(OH(2))(2)] (3), produced by reaction of H(6)mel with [Co(NH(3))(6)]Cl(3) is also presented. The magnetic susceptibility data for 1a-c, 2a-c, and 3 are presented. The susceptibility data for the Mn(II)- and Ni(II)-containing phases have been analyzed using a simple Mean Field Theory approach, and have been modeled using a high temperature series expansion. The comparative magnetism of the Co(II) phases is also presented, and is more complicated because of significant spin-orbit coupling effects.

Pyridine-2,4-dicarboxylate: a versatile building block for the preparation of functional coordination polymers.

The hydrothermal reaction of the pyridine-2,4-dicarboxylate (2,4-pdc) dianion with various 3d metal(II) cations resulted in the formation of a series of one-, two- and three-dimensional coordination polymers with varied network topologies. 2,4-pdc reacted directly with MnCI2 or FeCl2 in water at 200 degrees C under mild basic conditions to give a dense three-dimensional polymer, [M(2,4-pdc)] (M = Mn, 1a; M = Fe, 1b), which supports a highly-connected three-dimensional magnetic exchange lattice. Both 1a and 1b undergo antiferromagnetic ordering and the latter Fe(II)-containing material exhibited spin-canting behavior below 6.5 K. Reaction of 2,4-pdc with CoCl2 under identical conditions gave an unusual zigzag chain polymer, [Co4(2,4-pdc)4(OH2)10] (2), that has large amounts of coordinated H2O. The magnetism of 2 based on isolated Co(II) dimers was modeled using a modified van Vleck approach. Adjustment of the reaction pH resulted in the formation of additional Co(II)-containing materials with strongly contrasting structures: at lower pH in the presence of oxalic acid, the same reaction components gave a protonated molecular species, [Co(2,4-pdcH)2(OH2)2]. 2H2O (3); at higher pH in the presence of excess hydroxide, a highly porous, three-dimensional material was obtained, [Co3(micro3-OH)2(2,4-pdc)2] x 9H2O (4a). 4a contains cobalt hydroxide chains, whose magnetic behavior has been studied in detail by neutron diffraction. A Ni(II)-containing analogue was also prepared using NiCI2 (4b), which shows weak antiferromagnetic coupling. Attempts to obtain a Zn(II)-based analogue of the porous material 4 gave instead a unique coordination material, [Zn(micro2-OH)2(2,4-pdc)] (5), which contains uncommon zinc hydroxide bridging modes.

Hydro-thermal synthesis and crystal structure of poly[bis-(µ3-3,4-di-amino-benzoato)manganese], a layered coordination polymer.

The hydro-thermal synthesis and crystal structure of the title two-dimensional coordination polymer, poly[bis-(µ3-3,4-di-amino-benzoato-κ3 N 3,O,O')manganese(II)], [Mn(C7H7N2O2)2] n , are described. The Mn2+ cation (site symmetry ) adopts a tetra-gonally elongated trans-MnN2O4 octa-hedral coordination geometry and the µ3-N,O,O' ligand (bonding from both carboxyl-ate O atoms and the meta-N atom) links the metal ions into infinite (10) layers. The packing is consolidated by intra-layer N-H⋯O and inter-layer N-H⋯N hydrogen bonds. The structure of the title compound is compared with other complexes containing the C7H7N2O2 - anion and those of the related M(C8H8NO2)2 (M = Mn, Co, Ni, Zn) family, where C8H8NO2 - is the 3-amino-4-methyl-benzoate anion.

Non-classical behaviour in an S = 5/2 chain with next nearest neighbour interactions observed from the inelastic neutron scattering of Mn(2)(OD)(2)(C(4)O(4)).

Low-dimensional and frustrated magnetic systems often show interesting quantum phenomena. The use of large moments such as S = 5/2 within such materials is uncommon, partly due to the evidence that the large manifold of states associated with these centres results in pseudo-classical behaviour. Here we report on the inelastic neutron scattering of Mn(2)(OD)(2)(C(4)O(4)), a well-isolated chain with next nearest neighbour interactions. We observe a magnetic excitation spectrum below 30 K whose characteristics resemble those of quantum spin singlets. Inelastic neutron scattering from a powdered sample is shown to yield a great deal of information about the nature of these effects.

Synthesis, structure and physical properties of the manganese(ii) selenide/selenolate cluster complexes [Mn(32)Se(14)(SePh)(36)(PnPr(3))(4)] and [Na(benzene-15-crown-5)(C(4)H(8)O)(2)](2)[Mn(8)Se(SePh)(16)].

The synthesis, molecular structures, and magnetic and optical properties of [Mn(32)Se(14)(SePh)(36)(PnPr(3))(4)] and [Na(benzene-15-crown-5)(C(4)H(8)O)(2)](2)[Mn(8)Se(SePh)(16)] have been investigated which are the first examples of manganese chalcogenide cluster complexes, despite known manganese oxo compounds, which comprise more than four manganese atoms.

A new Co(II) coordination solid with mixed oxygen, carboxylate, pyridine and thiolate donors exhibiting canted antiferromagnetism with T(C) approximately 68 K.

Reaction of Co(II) chloride with the sodium salt of 2-mercaptonicotinic acid in water at 200 degrees C results in the formation of Co4(2-mna)4(H2O), which orders as a canted antiferromagnet at 68 K.

Dynamics of the frustrated spin in the low dimensional magnet Co3(OH)2(C4O4)2.

We describe powder inelastic neutron scattering experiments on a porous coordination polymer Co3(OH)2(C4O4)2, which has two different ordered magnetic phases known to display spin frustrated behaviour, resulting in an idle-spin phase. The moment on each ion is represented by an effective total angular moment J(eff ) = ½. A non-dispersive magnetic mode was observed in the idle-spin phase which is described by a simple dimer model that assumes ΔJ = 0. The excitation was found to persist well above the long range ordering temperature into the paramagnetic region. A combination of frustration, the J(eff) = ½ and low dimensionality may induce these quantum phenomena.

An unusual coordination polymer containing Cu(+) ions and featuring possible Cu...Cu `cuprophilic' interactions: poly[di-µ-chlorido-(µ4-3,5-diaminobenzoato-κ(4)O:O':N:N')tricopper(I)(3 Cu-Cu)].

Compounds containing copper(I) are of interest for their role in biological processes. The nature of short (< ∼ 3.2 Å) Cu...Cu contacts within these compounds has been debated, being either described as weakly attractive (bonding) `cuprophilic' interactions, or simply as short metal-metal distances constrained by ligand geometry or largely ionic in nature. The title three-dimensional Cu(+)-containing coordination polymer, [Cu3(C7H7N2O2)Cl2]n, was formed from the in situ reduction of CuCl2 in the presence of 3,5-diaminobenzoic acid and KOH under hydrothermal conditions. Its complex crystal structure contains ten distinct Cu(I) atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near-linear CuOCl and CuN2, T-shaped CuOCl2 and distorted tetrahedral CuOCl3 groups. Each Cu(I) atom is also associated with two adjacent metal atoms, with Cu...Cu distances varying from 2.7350 (14) to 3.2142 (13) Å; if all these are regarded as `cuprophilic' interactions, then infinite [-101] zigzag chains of Cu(I) atoms occur in the crystal. The structure is consolidated by N-H...Cl hydrogen bonds.

Synthesis, structure and properties of the manganese-doped polyoxotitanate cage [Ti18MnO30(OEt)20(MnPhen)3] (Phen = 1,10-phenanthroline).

The novel heterometallic polyoxotitanate cage [Ti18MnO30(OEt)20(MnPhen)3] (1), obtained by solvothermal reaction of Ti(OEt)4 with Mn(AcO)3·(H2O)2 and 1,10-phenanthroline (Phen) in EtOH, has a C3 symmetric core structure containing an interstitial tetrahedral Mn(II) ion and is surrounded by three Mn(II)(Phen) fragments. The molecular structure is retained in thin film electrodes of 1 deposited by solution drop-casting onto fluorinated tin oxide (FTO). Both solid state and solution phase electrochemical measurements show dual redox couples, consistent with the two distinct Mn coordination environments in the cage structure. Sintering of 1 in air at 600 °C produces a black crystalline solid which consists of Mn-doped TiO2 (mainly in the rutile phase) together with α-Mn2O3. Such a composite semiconductor has an optical band gap of ca. 1.80 eV, similar to that of α-Mn2O3.

Layered metal organosulfides: hydrothermal synthesis, structure and magnetic behaviour of the spin-canted magnet Co(1,2-(O2C)(S)C6H4).

Reaction of cobalt(II) salts with the thiosalicylate dianion under hydrothermal conditions yields green lamellar Co((O2C)(S)C6H4) which displays canted antiferromagnetism.

Syntheses and magnetic properties of hexanuclear [Cp2Mn3(L1)4]2 and octanuclear [Mn8(L2)12(mu 4-O)2] (L1 = 2-HNC5H5N, L2 = 2-NH-3-Br-5-MeC5H3N, Cp = C5H5).

The reactions of manganocene, Cp2Mn, with 2-aminopyridine (L1H) or 2-amino-3-bromo-5-methylpyridine (L2H) give the novel hexanuclear and octanuclear Mn(II) amido cage compounds [Cp2Mn3(L1)4]2 (1) and [Mn8(L2)12(mu 4-O)2] (2); magnetic measurements on which provide a rare insight into the magnetic properties of amido-bridged metal clusters.

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania.

To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).

Reactions of Cp2M (M = Ni, V) with dilithium diamido-aryl reagents; retention and oxidation of the transition metal ions.

The reactions of dilithium 1,2-diamidobenzene, [1,2-(HN)2C6H4]Li2 (L(1)H2)Li2, and dilithium 1,8-diamidonaphthalene, [1,8-(NH)2C10H6]Li2 (L(2)H2)Li2, with Cp2Ni and Cp2V have been used to obtain the new complexes (L(2)H2)2Ni{Li(THF)2}2 (3), (L(2)H2)3V{Li(THF)2}3 (4) and (L(1)H2)6Ni6·{[(L(1)H2)3(L(1)H)3Ni6Li(THF)](2-)·2[Li(THF)4](+)} (5), in which retention or oxidation of the initial metal(ii) centre is observed. Whereas 3 and 4 contain one transition metal ion within ion-paired structures, 5 has a complicated co-crystalline composition which contains octahedral Ni6-cages constructed from six square-planar (16e) Ni(II) centres.