CCR2-dependent CX3CR1+ colonic macrophages promote Enterococcus faecalis dissemination.

Enterococci are common commensal bacteria that colonize the gastrointestinal tracts of most mammals, including humans. Importantly, these bacteria are one of the leading causes of nosocomial infections. This study examined the role of colonic macrophages in facilitating Enterococcus faecalis infections in mice. We determined that depletion of colonic phagocytes resulted in the reduction of E. faecalis dissemination to the gut-draining mesenteric lymph nodes. Furthermore, we established that trafficking of monocyte-derived CX3CR1-expressing macrophages contributed to E. faecalis dissemination in a manner that was not reliant on CCR7, the conventional receptor involved in lymphatic migration. Finally, we showed that E. faecalis mutants with impaired intracellular survival exhibited reduced dissemination, suggesting that E. faecalis can exploit host immune cell migration to disseminate systemically and cause disease. Our findings indicate that modulation of macrophage trafficking in the context of antibiotic therapy could serve as a novel approach for preventing or treating opportunistic infections by disseminating enteric pathobionts like E. faecalis.

Influence of Cation Substitution on Cycling Stability and Fe-Cation Migration in Li3Fe3-xMxTe2O12 (M = Al, In) Cathode Materials.

Li3Fe3Te2O12 adopts a crystal structure, described in space group Pnnm, related to that of LiSbO3, in which Te6+, Fe3+, and Li+ cations reside in a partially ordered configuration within an hcp array of oxide ions. Chemical or electrochemical insertion of lithium is accompanied by a fully reversible migration of some of the Fe cations with an initial capacity of 120 mA h g-1 (2.85 Li per formula unit). Long-term cycling stability is limited by the facile reduction of Te6+ to elemental Te, which leads to cathode decomposition. Partial substitution of Fe by In suppresses Te6+ reduction, such that Li3Fe2InTe2O12 shows no sign of this cathode decomposition pathway, even after 100 cycles. In contrast, Al-for-Fe substitution is chemically limited to Li3Fe2.6Al0.4Te2O12 and appears to have almost no influence on cathode longevity. These features of the Li3Fe3-xMxTe2O12 system are discussed on the basis of a detailed structural analysis performed using neutron and synchrotron X-ray diffraction.

Disproportionation of Co2+ in the Topochemically Reduced Oxide LaSrCoRuO5.

Complex transition-metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition-metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO6 , using Zr, yields LaSrCoRuO5 . This reduced phase contains an ordered array of apex-linked square-based pyramidal Ru3+ O5 , square-planar Co1+ O4 and octahedral Co3+ O6 units, consistent with the coordination-geometry driven disproportionation of Co2+ . Coordination-geometry driven disproportionation of d7 transition-metal cations (e.g. Rh2+ , Pd3+ , Pt3+ ) is common in complex oxides containing 4d and 5d metals. However, the weak ligand field experienced by a 3d transition-metal such as cobalt leads to the expectation that d7+ Co2+ should be stable to disproportionation in oxide environments, so the presence of Co1+ O4 and Co3+ O6 units in LaSrCoRuO5 is surprising. Low-temperature measurements indicate LaSrCoRuO5 adopts a ferromagnetically ordered state below 120 K due to couplings between S=1 /2 Ru3+ and S=1 Co1+ .

MnCaTa2O7-A Magnetically Ordered Polar Phase Prepared via Cation Exchange.

Reaction between the pseudo-Ruddlesden-Popper phase Li2CaTa2O7 and MnCl2 at 375 °C yields MnCaTa2O7, a paramagnetic polar phase (space group P21nm), which adopts an a-b-c+/b-a-c+ distorted, layered perovskite structure. Magnetization and neutron diffraction data show that MnCaTa2O7 adopts an antiferromagnetically ordered state below TN = 56 K and exhibits large lattice parameter anomalies and a transient increase in its polar distortion mode at TA = 50 K. However, in contrast to the related phase MnSrTa2O7, MnCaTa2O7 shows no strong signature of weak ferromagnetism and thus shows no signs of magnetoelectric coupling. The differences in physical behavior between the two MnATa2O7 phases appear to be related to their differing Mn cation-order and differing TaO6 tilting schemes and demonstrate that even subtle changes to these orderings can have large effects on the distortion-mode couplings, which drive complex behavior of this class of "hybrid improper" ferroelectric material.

Ca2MnO3X (X = Cl, Br) Oxyhalides with 1-Dimensional Ferromagnetic Chains of Square-Planar S = 2 Mn3.

Mixed anion oxyhalides with the formula Ca2MnO3X (X = Cl, Br) are synthesized using solid-state reaction methods. These two materials crystallize in a novel structure type due to the small ionic radius of Ca and the strong Jahn-Teller effect of Mn3+. The resulting structure (space group Cmcm) contains one-dimensional chains of MnO4 square planes, with an angle of ∼120° between neighboring planes. At low temperatures, the two materials adopt magnetic arrangements, with ferromagnetic chains coupled antiferromagnetically. On applying a magnetic field, both materials experience spin-flop transitions.

Fluorochemicals from fluorspar via a phosphate-enabled mechanochemical process that bypasses HF.

All fluorochemicals-including elemental fluorine and nucleophilic, electrophilic, and radical fluorinating reagents-are prepared from hydrogen fluoride (HF). This highly toxic and corrosive gas is produced by the reaction of acid-grade fluorspar (>97% CaF2) with sulfuric acid under harsh conditions. The use of fluorspar to produce fluorochemicals via a process that bypasses HF is highly desirable but remains an unsolved problem because of the prohibitive insolubility of CaF2. Inspired by calcium phosphate biomineralization, we herein disclose a protocol of treating acid-grade fluorspar with dipotassium hydrogen phosphate (K2HPO4) under mechanochemical conditions. The process affords a solid composed of crystalline K3(HPO4)F and K2-xCay(PO3F)a(PO4)b, which is found suitable for forging sulfur-fluorine and carbon-fluorine bonds.

Complex Magnetic Order in Topochemically Reduced Rh(I)/Rh(III) LaM0.5Rh0.5O2.25 (M = Co, Ni) Phases.

Topochemical reduction of the cation-disordered perovskite oxides LaCo0.5Rh0.5O3 and LaNi0.5Rh0.5O3 with Zr yields the partially anion-vacancy ordered phases LaCo0.5Rh0.5O2.25 and LaNi0.5Rh0.5O2.25, respectively. Neutron diffraction and Hard X-ray photoelectron spectroscopy (HAXPES) measurements reveal that the anion-deficient phases contain Co1+/Ni1+ and a 1:1 mixture of Rh1+ and Rh3+ cations within a disordered array of apex-linked MO4 square-planar and MO5 square-based pyramidal coordination sites. Neutron diffraction data indicate that LaCo0.5Rh0.5O2.25 adopts a complex antiferromagnetic ground state, which is the sum of a C-type ordering (mM5+) of the xy-components of the Co spins and a G-type ordering (mΓ1+) of the z-components of the Co spins. On warming above 75 K, the magnitude of the mΓ1+ component declines, attaining a zero value by 125 K, with the magnitude of the mM5+ component remaining unchanged up to 175 K. This magnetic behavior is rationalized on the basis of the differing d-orbital fillings of the Co1+ cations in MO4 square-planar and MO5 square-based pyramidal coordination sites. LaNi0.5Rh0.5O2.25 shows no sign of long-range magnetic order at 2 K - behavior that can also be explained on the basis of the d-orbital occupation of the Ni1+ centers.

The crystal and defect structures of polar KBiNb2O7.

KBiNb2O7 was prepared from RbBiNb2O7 by a sequence of cation exchange reactions which first convert RbBiNb2O7 to LiBiNb2O7, before KBiNb2O7 is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNb2O7 adopts a polar, layered, perovskite structure (space group A11m) in which the BiNb2O7 layers are stacked in a (0, ½, z) arrangement, with the K+ cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi3+ cations parallel to the y-axis. HAADF-STEM images reveal that KBiNb2O7 exhibits frequent stacking faults which convert the (0, ½, z) layer stacking to (½, 0, z) stacking and vice versa, essentially switching the x- and y-axes of the material. By fitting the complex diffraction peak shape of the SXRD data collected from KBiNb2O7 it is estimated that each layer has approximately a 9% chance of being defective - a high level which is attributed to the lack of cooperative NbO6 tilting in the material, which limits the lattice strain associated with each fault.

Microstructural Activation of a Topochemical Reduction Reaction.

The progress of the topochemical reduction reaction that converts LaSrNiRuO6 into LaSrNiRuO4 depends on the synthesis conditions used to prepare the oxidized phase. Samples of LaSrNiRuO6 that have been quenched from high temperature can be readily and rapidly converted into LaSrNiRuO4. In contrast, samples that have been slow-cooled cannot be completely reduced. This reactivity difference is attributed to the differing microstructures of the quenched and slow-cooled samples, with the former having much smaller average crystalline domain sizes and larger lattice strains than the latter. A mechanism to explain this effect is presented, in which the greater "plasticity" of small crystalline domains helps lower the activation energy of the reduction reaction. In addition, we propose that the enhanced lattice strain in quenched samples also acts to destabilize the host phase, further enhancing reactivity. These observations suggest that the microstructure of a material can be used to "activate" topochemical reactions in the solid state, expanding the scope of phases that can be prepared by this type of reaction.

The influence of the 6s2 configuration of Bi3+ on the structures of A'BiNb2O7 (A' = Rb, Na, Li) layered perovskite oxides.

Solid state compounds which exhibit non-centrosymmetric crystal structures are of great interest due to the physical properties they can exhibit. The 'hybrid improper' mechanism - in which two non-polar distortion modes couple to, and stabilize, a further polar distortion mode, yielding an acentric crystal structure - offers opportunities to prepare a range of novel non-centrosymmetric solids, but examples of compounds exhibiting acentric crystal structures stabilized by this mechanism are still relatively rare. Here we describe a series of bismuth-containing layered perovskite oxide phases, RbBiNb2O7, LiBiNb2O7 and NaBiNb2O7, which have structural frameworks compatible with hybrid-improper ferroelectricity, but also contain Bi3+ cations which are often observed to stabilize acentric crystal structures due to their 6s2 electronic configurations. Neutron powder diffraction analysis reveals that RbBiNb2O7 and LiBiNb2O7 adopt polar crystal structures (space groups I2cm and B2cm respectively), compatible with stabilization by a trilinear coupling of non-polar and polar modes. The Bi3+ cations present are observed to enhance the magnitude of the polar distortions of these phases, but are not the primary driver for the acentric structure, as evidenced by the observation that replacing the Bi3+ cations with Nd3+ cations does not change the structural symmetry of the compounds. In contrast the non-centrosymmetric, but non-polar structure of NaBiNb2O7 (space group P212121) differs significantly from the centrosymmetric structure of NaNdNb2O7, which is attributed to a second-order Jahn-Teller distortion associated with the presence of the Bi3+ cations.

Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides.

LaxSr2-xNiRuO6, LaxSr4-xNiRuO8, and LaxSr3-xNiRuO7 are, respectively, the n = ∞, 1, and 2 members of the (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n+1 compositional series. Reaction with CaH2, in the case of the LaxSr2-xNiRuO6 perovskite phases, or Zr oxygen getters in the case of the LaxSr4-xNiRuO8 and LaxSr3-xNiRuO7 Ruddlesden-Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n-1 compounds (LaxSr2-xNiRuO4, LaxSr4-xNiRuO6, and LaxSr3-xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+ and Ru2+ centers they contain. Increasing the La3+ concentration (x > 1) leads to a reduction of some of the Ru2+ centers to Ru1+ centers and a suppression of the ferromagnetic state (lower Tc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+ concentration (x < 1) oxidizes some of the Ru2+ centers to Ru3+ centers and enhances the ferromagnetic coupling (increased Tc, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.

Directed synthesis of a hybrid improper magnetoelectric multiferroic material.

Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li2SrTa2O7, which adopts a polar structure due to a cooperative tilting of its constituent TaO6 octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa2O7, can be prepared. On cooling below 43 K the Mn2+ centres in MnSrTa2O7 adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.

LaSrCo0.5Rh0.5O3.25 and LaSrNi0.5Rh0.5O3.25:Topochemically Reduced, Mixed Valence Rh(I)/Rh(III) Oxides.

Topochemical reduction of the n = 1 Ruddlesden-Popper phases LaSrCo0.5Rh0.5O4 and LaSrNi0.5Rh0.5O4 with Zr yields LaSrCo0.5Rh0.5O3.25 and LaSrNi0.5Rh0.5O3.25, respectively. Magnetization and XPS data reveal that while the rhodium centers in LaSrCo0.5Rh0.5O3.25 and LaSrNi0.5Rh0.5O3.25 have an average oxidation state of Rh2+, these are actually mixed valence Rh(I,III) compounds, with the disproportionation of Rh2+ driven by the favorability of locating d8 Rh1+ and d6 Rh3+ cations within square-planar and square-based pyramidal coordination sites, respectively.

Structure and magnetism of the Rh4+-containing perovskite oxides La0.5Sr0.5Mn0.5Rh0.5O3 and La0.5Sr0.5Fe0.5Rh0.5O3.

Synchrotron X-ray powder diffraction data indicate that La0.5Sr0.5Mn0.5Rh0.5O3 and La0.5Sr0.5Fe0.5Rh0.5O3 adopt distorted perovskite structures (space group Pnma) with A-site and B-site cation disorder. A combination of XPS and 57Fe Mössbauer data indicate the transition metal cations in the two phases adopt Mn3+/Rh4+ and Fe3+/Rh4+ oxidation state combinations respectively. Transport data indicate both phases are insulating, with ρ vs. T dependences consistent with 3D variable-range hopping. Magnetisation data reveal that La0.5Sr0.5Mn0.5Rh0.5O3 adopts a ferromagnetic state below Tc ∼ 60 K, which is rationalized on the basis of coupling via a dynamic Jahn-Teller distortion mechanism. In contrast, magnetic data reveal La0.5Sr0.5Fe0.5Rh0.5O3 undergoes a transition to a spin-glass state at T ∼ 45 K, attributed to frustration between nearest-neighbour Fe-Rh and next-nearest-neighbour Fe-Fe couplings.

Evidence of Paracrystalline Cation Order in the Ruddlesden-Popper Phase LaSr3NiRuO8 through Neutron Total Scattering Techniques.

Cation ordering in perovskite-derived phases can lead to a wealth of tunable physical properties. Ordering is typically driven by a large difference between the cation size and charge, but many Ruddlesden-Popper phases An+1BnO3n+1 appear to lack such B-site ordering, even when these differences are present. One such example is the "double" Ruddlesden-Popper n = 1 composition LaSr3NiRuO8. In this material, a lack of B-site ordering is observed through traditional crystallographic techniques, but antiferromagnetic ordering in the magnetism data suggests that B-site cation ordering is indeed present. Neutron total scattering, particularly analysis of the neutron pair distribution function, reveals that the structure is locally B-site-ordered below 6 Å but becomes slightly disordered in the midrange structure around 12 Å. This provides evidence for paracrystalline order in this material: cation ordering within a single perovskite sheet that lacks perfect registry within the three-dimensional stack of sheets. This work highlights the importance of employing a structural technique that can probe both the local and midrange order in addition to the crystallographic structure and provides a structural origin to the observed magnetic properties of LaSr3NiRuO8. Further, it is proposed that paracrystalline order is likely to be common among these layered-type oxides.

A Structurally Characterized Cobalt(I) σ-Alkane Complex.

A cobalt σ-alkane complex, [Co(Cy2 P(CH2 )4 PCy2 )(norbornane)][BArF 4 ], was synthesized by a single-crystal to single-crystal solid/gas hydrogenation from a norbornadiene precursor, and its structure was determined by X-ray crystallography. Magnetic data show this complex to be a triplet. Periodic DFT and electronic structure analyses revealed weak C-H→Co σ-interactions, augmented by dispersive stabilization between the alkane ligand and the anion microenvironment. The calculations are most consistent with a η1 :η1 -alkane binding mode.

Hole and Electron Doping of the 4d Transition-Metal Oxyhydride LaSr3 NiRuO4 H4.

Hole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion-exchange) is extremely challenging as these low-temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition-metal oxyhydride LaSr3 NiRuO4 H4 by first preparing precursors in the range Lax Sr4-x NiRuO8 0.5

Pressure-Induced Transitions in the 1-Dimensional Vanadium Oxyhydrides Sr2VO3H and Sr3V2O5H2, and Comparison to 2-Dimensional SrVO2H.

High-pressure X-ray diffraction measurements on the layered oxyhydrides Sr2VO3H and Sr3V2O5H2 reveal that both compounds undergo a pressure-induced rock-salt to CsCl (B1-B2) structural transition, similar to those observed in binary compounds (oxides, halides, chalcogenides, etc.). This structural transition, observed at 43 and 45 GPa in Sr2VO3H and Sr3V2O5H2, respectively, relieves almost all of the accumulated strain on the infinite V-O-V ladders, such that the V-O bond lengths are almost identical at 0 and 50 GPa but are substantially compressed at intermediate pressures. The resistances of both materials with 1-dimensional VO ladders decrease with increasing pressure, but unlike SrVO2H that contains 2-dimensional VO2 sheets, they remain insulating even at the highest accessible pressures. The reduction in dimensionality from planar to linear VO networks reduces the dispersion of the V-O π bands that define the band gap and leads to insulating behavior at all measured pressures.

Exsolution of SrO during the Topochemical Conversion of LaSr3CoRuO8 to the Oxyhydride LaSr3CoRuO4H4.

 Reaction of the n = 1 Ruddlesden-Popper oxide LaSr3CoRuO8 with CaH2 yields the oxyhydride phase LaSr3CoRuO4H4 via a topochemical anion exchange. Close inspection of the X-ray and neutron powder diffraction data in combination with HAADF-STEM images reveals that the nanoparticles of SrO are exsolved from the system during the reaction, with the change in cation stoichiometry accommodated by the inclusion of n > 1 (Co/Ru)nOn+1H2n "perovskite" layers into the Ruddlesden-Popper stacking sequence. This novel pseudotopochemical process offers a new route for the formation of n > 1 Ruddlesden-Popper structured materials. Magnetization data are consistent with a LaSr3Co+Ru2+O4H4 (Co+, d8, S = 1; Ru2+, d6, S = 0) oxidation/spin state combination. Neutron diffraction and µ+SR data show no evidence for long-range magnetic order down to 2 K, suggesting the diamagnetic Ru2+ centers impede the Co-Co magnetic-exchange interactions.

CaMn0.5Ir0.5O2.5: An Anion-Deficient Perovskite Oxide Containing Ir3.

Reaction between CaMn0.5Ir0.5O3 and NaH, either through solid-solid contact or via a gas mediated reaction process, yields the topochemically reduced phase CaMn0.5Ir0.5O2.5 in which Mn3+ and Ir3+ cations are located within a partially anion-vacancy disordered lattice. Magnetization data from CaMn0.5Ir0.5O2.5 can be fit by the Curie-Weiss law to yield C = 1.586 cm3 K mol-1 and θ = -86.9 K, consistent with a combination of S = 2, Mn3+ and S = 0, Ir3+. On cooling below T ∼ 110 K, the system undergoes a transition to a spin-glass state, consistent with the observed Mn/Ir cation disorder and frustration between Mn-O-Mn and Mn-O-Ir-O-Mn magnetic couplings. The degree of reduction and the observed anion-vacancy disorder are discussed on the basis of the d-orbital filling of the transition-metal cations.