Jin-Xiao Mi

Strong spin frustration from isolated triangular Cu(II) trimers in SrCu(OH)3Cl with a novel cuprate layer

Strontium oxocuprates such as Sr2CuO2Cl2 have been extensively investigated for their two-dimensional (2D) planar CuO2 square layers that are typical of high-temperature cuprate superconductors. A new synthetic strontium cuprate SrCu(OH)3Cl features a novel cuprate layer with isolated triangular Cu(II) trimers. The crystal structure of the title compound can be derived from breaking the cuprate planar layer to form isolated, nonplanar triangular copper trimers ({[Cu3(μ3-Cl)(OH)3](OH)6Cl2}6−), which are connected by strontium coordination spheres to form a novel framework structure. The copper trimers exhibit an unprecedented array that has triangular Cu3-planes perpendicular not only to their own layer but also to their counterparts in the next layers, which is thus different from the parallel array in the Kagome layer of ZnCu3(OH)6Cl2. This cross-orientation arrangement of the triangular Cu(II) trimers is proposed to be responsible for a strong antiferromagnetic exchange (J = −233(2) cm−1) in the triangles characterized by a Weiss temperature θcw = −135 K but virtually zero (or negligible) magnetic coupling between the triangles. Such remarkable magnetic properties make the title compound a Mott insulator – an ordered inorganic solid with Cu spin-1/2 spins forming an intrinsic “molecular magnet”.

Perfect Kagomé lattices in YCu3(OH)6Cl3: a new candidate for the quantum spin liquid state

Polymorphs of ZnCu3(OH)6Cl2 (herbertsmithite and kapellasite) and related cuprates MCu3(OH)6Cl2 (M = Mg2+, Ca2+, Cd2+, Co2+, Fe2+, Mn2+ and Ni2+) with antiferromagnetic Kagome lattices have attracted attention for intensively investigating the quantum spin liquid (QSL) materials. However, mixing between magnetic (Cu2+) and diamagnetic divalent ions (Zn2+, Mg2+, etc.) is commonly significant in MCu3(OH)6Cl2 and therefore disturbs the perfect Kagome lattices consequently adversely affecting the magnetic performance. Herein we report on the synthesis and characterization of YCu3(OH)6Cl3, the first-ever cuprate of the kapellasite-type structure with a trivalent cation. Single-crystal X-ray structure refinements show that the diamagnetic Y3+ cations in the title compound are located at the Zn positions and are charge balanced by additional Cl− anions between the Kagome layers. 65Cu and 35Cl MAS NMR analyses confirm single-crystal X-ray diffraction data that there is no detectable mixing between Y3+ and Cu2+ in the title compound, resulting in a more idealized Kagome lattice than those in herbertsmithite and kapellasite. Magnetic analyses demonstrate that the title compound is a geometrically frustrated S = 1/2 antiferromagnet with a Curie–Weiss temperature θ of −99 K and does not show any magnetic transition down to 2 K (i.e., the frustration parameter f > 49), suggesting a possible QSL candidate.

Two Isotypic Transition Metal Germanophosphates MII4(H2O)4[Ge(OH)2(HPO4)2(PO4)2] (MII = Fe, Co): Synthesis, Structure, Mössbauer Spectroscopy, and Magnetic Properties

Synthetic, structural, thermogravimetric, Mössbauer spectroscopic, and magnetic studies were performed on two new isotypic germanophosphates, M(II)(4)(H(2)O)(4)[Ge(OH)(2)(HPO(4))(2)(PO(4))(2)] (M(II) = Fe, Co), which have been prepared under hydro-/solvo-thermal conditions. Their crystal structures, determined from single crystal data, are built from zigzag chains of M(II)O(6)-octahedra sharing either trans or skew edges interconnected by [GeP(4)O(14)(OH)(4)](8-) germanophosphate pentamers to form three-dimensional neutral framework structure. The edge-sharing M(II)O(6)-octahedral chains lead to interesting magnetic properties. These two germanophosphates exhibit a paramagnetic to antiferromagnetic transition at low temperatures. Additionally, two antiferromagnetic ordering transitions at around 8 and 6 K were observed for cobalt compound while only one at 19 K for the iron compound. Low-dimensional magnetic correlations within the octahedral chains are also observed. The divalent state of Fe in the iron compound determined from the Mössbauer study and the isothermal magnetization as well as thermal analyses are discussed.

Structural Assembly from Phosphate to Germanophosphate by Applying Germanate as a Binder

Structural assembly from phosphate to germanophosphate by applying germanate as a binder has been achieved. Two isotypic porous compounds, K3[M(II)4(HPO4)2][Ge2O(OH)(PO4)4]·xH2O (M(II) = Fe, Cd; x = 2 for Fe and 3 for Cd, denoted as KFeGePO-1 and KCdGePO-1, respectively), contain a known transition-metal phosphate (TMPO) layer, (∞)(2){[M2(HPO4)3]2–}, which is built from chains of trans-edge-sharing MO6 octahedra bridged by MO5 trigonal bipyramids that were further linked and decorated by phosphate tetrahedra. The layers are bound by infinite chains of GeO5(OH) octahedra, resulting in a 3D open-framework structure with 1D 12-ring channels that are occupied by K+ ions and water molecules. The curvature of the TMPO layers and shape of the 12-ring windows can be tuned by the transition metals because of their Jahn–Teller effect.

11B MAS NMR and First-Principles Study of the [OBO3] Pyramids in Borates

Borates are built from the [Bϕ3] planar triangles and the [Bϕ4] tetrahedral groups, where ϕ denotes O or OH. However, the [Bϕ4] groups in some borates are highly distorted to include three normal B-O bonds and one anomalously long B-O bond and, therefore, are best described as the [OBO3] pyramids. Four synthetic borates of the boracite-type structures (Mg3B7O13Br, Cu3B7O13Br, Zn3B7O13Cl, and Mg3B7O13Cl) containing a range of [OBO3] pyramids were investigated by multifield (7.05, 14.1, and 21.1 T) (11)B magic-angle spinning nuclear magnetic resonance (MAS NMR), triple quantum (3Q) MAS NMR experiments, as well as density functional theory calculations. The high-resolution (11)B MAS NMR spectra supported by theoretical predictions show that the [OBO3] pyramids are characterized by isotropic chemical shifts δiso((11)B) from 1.4(1) to 4.9(1) ppm and nuclear quadrupole parameters CQ((11)B) up to 1.3(1) MHz, both significantly different from those of the [BO4] and [BO3] groups in borates. These δiso((11)B) and CQ((11)B) values indicate that the [OBO3] pyramids represent an intermediate state between the [BO4] tetrahedra and [BO3] triangles and demonstrate that the (11)B NMR parameters of four-coordinate boron oxyanions are sensitive to local structural environments. The orientation of the calculated unique electronic field gradient tensor element Vzz of the [OBO3] pyramids is aligned approximately along the direction of the anomalously long B-O bond, corresponding to B-2pz with the lowest electron density.

Single-crystal microtubes of a novel apatite-type compound, (Na2.5Bi2.5)(PO4)3(F,OH), with well-faceted hexagonal cross sections

A novel apatite-type compound, (Na2.5Bi2.5)(PO4)3(F,OH), NBPF, in the form of single-crystal microtubes with well-faceted, hexagonal morphologies in both exterior and interior surfaces, has been synthesized under hydrothermal conditions without addition of any template, surfactant or metal catalyst. Single crystal X-ray diffraction analysis confirms that Na+ and Bi3+ ions completely replace the Ca2+ ions in the apatite-like structure and jointly occupy three crystallographic sites with significantly different site preferences [Bi0.61Na0.39 at the 6c site, and Bi0.45Na0.55 and Bi0.23Na0.77 at the 2b sites, space groupP63 (No. 173)]. Time-dependent experiments show that these NBPF microtubes form via a fluoride-induced, in situ chemical reaction nucleation–dissolution–recrystallization growth mechanism.

Cerium(III) dihydroxidohexa­oxidotetra­borate chloride

The crystal structure of the title compound, Ce[B4O6(OH)2]Cl, is built from polyborate sheets parallel to the (001) plane. These sheets stack along the [001] direction and are linked by Ce atoms exhibiting an CeO8Cl2 coordination sphere. O—H⋯O and O—H⋯Cl hydrogen bonds additionally stabilize the structural set-up. The polyborate sheet is made up of zigzag borate chains running along the [10] direction. These zigzag chains are interconnected by shared O-vertices, resulting in a two-dimensional layer with nine-membered rings. All B and O atoms (except for the terminal OH atoms) lie in the nearly planar sheets of polyborates, leading to their isotropic atomic displacement parameters being significantly smaller than usual. This may be attributed to the fact that the atomic displacement parameters correlate not only with their atomic masses but with their coordination environments also.

Raman investigation on the behavior of parasibirskite CaHBO3 at high pressure.

Knowledge about the stability of hydrous borates and borosilicates at high pressures are of critical importance to our understanding on the boron geochemical cycle. Raman spectroscopic measurements of parasibirskite CaHBO3, containing the [BO2(OH)] groups, have been made to pressures up to 5.4GPa. The Raman data show that a progressive structural evolution from ambient pressure to 5.4GPa can be accounted for by the same monoclinic phase P21/m, where the splitting of several Raman bands observed at some pressures is interpreted as the effect of the complex disordering in the H-bond network that has bifurcated H-bonds and ½-occupied H sites. There is no unambiguous evidence for phase transition to the ordered P21 monoclinic phase predicted by first-principles calculations at T=0K (W. Sun et al., Can. Miner., 2011). On the contrary, the disordering of parasibirskite, evidenced by the widening and attenuating Raman spectra, increases markedly at high pressures above 4.5GPa that results in incipient amorphization. Comparison of theoretical (lattice-dynamical) and experimental Raman spectra allows the reliable interpretation of almost all observed bands. The strongest symmetric B-O stretching band v1 at the wavenumber 908cm-1, which is split into a doublet at high pressures, exhibits a shift rate of 4.22cm-1/GPa for the main component.

Tetra­aqua­tetra­manganese(II) catena-[germanodihydroxidodi(hydrogen­phosphate)diphosphate]

The title compound, Mn4(H2O)4[Ge(OH)2(HPO4)2(PO4)2], was synthesized by the solvothermal method. Its crystal structure is isotypic with the iron and cobalt analogues [Huang et al. (2012 ▶). Inorg. Chem. 51, 3316–3323]. In the crystal structure, the framework is built from undulating manganese phosphate sheets parallel to (010) interconnected by GeO6 octahedra (at the inversion center), resulting in a three-dimensional network with eight-membered ring channels into which all the protons point. The undulating manganese phosphate sheet consists of zigzag manganese octahedral chains along [10-1], built from MnO4(OH)(OH2) octahedra and MnO5(OH2) octahedra by sharing their trans or skew edges, which are interconnected by PO3(OH) and PO4 tetrahedra via corner-sharing. The crystal structure features extensive O—H⋯O hydrogen-bonding interactions.

Redetermination of Ce[B5O8(OH)(H2O)]NO3·2H2O

The crystal structure of Ce[B5O8(OH)(H2O)]NO3·2H2O, cerium(III) aquahydroxidooctaoxidopentaborate nitrate dihydrate, has been redetermined from single-crystal X-ray diffraction data. In contrast to the previous determination [Li et al. (2003 ▶). Chem. Mater. 15, 2253–2260], the present study reveals the location of all H atoms, slightly different fundamental building blocks (FBBs) of the polyborate anions, more reasonable displacement ellipsoids for all non-H atoms, as well as a model without disorder of the nitrate anion. The crystal structure is built from corrugated polyborate layers parallel to (010). These layers, consisting of [B5O8(OH)(H2O)]2− anions as FBBs, stack along [010] and are linked by Ce3+ ions, which exhibit a distorted CeO10 coordination sphere. The layers are additionally stabilized via O—H⋯O hydrogen bonds between water molecules and nitrate anions, located at the interlayer space. The [BO3(H2O)]-group shows a [3 + 1] coordination and is considerably distorted from a tetrahedral configuration. Bond-valence-sum calculation shows that the valence sum of boron is only 2.63 valence units (v.u.) when the contribution of the water molecule (0.49 v.u.) is neglected.