Paul T. Wood

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.

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.

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<sup>+</sup>-containing coordination polymer, [Cu<sub>3</sub>(C<sub>7</sub>H<sub>7</sub>N<sub>2</sub>O<sub>2</sub>)Cl<sub>2</sub>]<sub>n</sub>, was formed from thein situreduction of CuCl<sub>2</sub>in the presence of 3,5-diaminobenzoic acid and KOH under hydrothermal conditions. Its complex crystal structure contains ten distinct Cu<sup>I</sup>atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near-linear CuOCl and CuN<sub>2</sub>, T-shaped CuOCl<sub>2</sub>and distorted tetrahedral CuOCl<sub>3</sub>groups. Each Cu<sup>I</sup>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 [\overline{1}01] zigzag chains of Cu^Iatoms occur in the crystal. The structure is consolidated by N—H...Cl hydrogen bonds.

The syntheses and crystal structures of the layered coordination polymers M(C8H8NO2)2 [M = Mn ( 1), Co ( 2), Ni ( 3) and Zn ( 4)] are described. These isostructural compounds contain centrosymmetric ...

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.

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.

During an investigation of the synthesis of the new mono- and bis(guanidinate) complexes [{iPr2NC(···NiPr)2}GaCl2] (2) and [{iPr2NC(···NiPr)2}2GaCl] (3) from the in situ reactions of the lithium guanidinate [{iPr2NC(···NiPr)2}Li]n (1) with GaCl3, an unexpected new guanidinate expansion reaction was uncovered in which it is found that the nucleophilic addition of 2 to the carbodiimide, iPrN=C=NiPr, gives [iPrN{C(NiPr)=NiPr}{C(=NiPr)NiPr2}GaCl2] (4), containing an unusual bis(diguanidinate) ligand.

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).

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.

The reactions of dilithium 1,2-diamidobenzene, [1,2-(HN)₂C₆H₄]Li₂ (L¹111H₂222)Li₂, and dilithium 1,8-diamidonaphthalene, [1,8-(NH)₂C₁₀H₆]Li₂ (L²22H₂22)Li₂, with Cp₂Ni and Cp₂V have been used to obtain the new complexes (L²22H₂22)₂Ni{Li(THF)₂}₂ (3), (L²22H₂22)₃V{Li(THF)₂}₃ (4) and (L¹111H₂222)₆Ni₆·{[(L¹111H₂222)₃(L¹1H)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.