Oxidation state variation in bis-calix[4]arene supported decametallic Mn clusters

The reaction of MnCl2·4H2O, H8L (2,2’-bis-p-tBu-calix[4]arene) and NEt3 in a dmf/MeOH solvent mixture results in the formation of a mixed valent decametallic cluster of formula [MnII6MnIII4(L)2(µ3-OH)4(µ-OH)4(MeOH)4(dmf)4(MeCN)2]·MeCN (3). Complex 3 crystallises in the monoclinic space group P21/n with the asymmetric unit comprising half of the compound. Structure solution reveals that the bis-calix[4]arene ligands are arranged such that one TBC[4] moiety in each has undergone inversion in order to accommodate a [MnIII4MnII6] metallic skeleton that describes three vertex-sharing [MnIII2MnII2] butterflies. The structure is closely related to the species [MnIII6MnII4(L)2(μ3-O)2(μ3-OH)2(μ-OMe)4(H2O)4(dmf)8]·4dmf (4), the major difference being the oxidation level of the Mn ions in the core of the compound. DFT calculations on the full structures reveal that replacing the MnIII ions in 4 for MnII ions in 3 results in a significant decrease in the magnitude of some antiferromagnetic exchange contributions, a switch from ferromagnetic to antiferromagnetic in others, and the loss of significant spin frustration.

Copper-hydride nanoclusters with enhanced stability by N-heterocyclic carbenes

Copper-hydrides have been intensively studied for a long time due to their utilization in a variety of technologically important chemical transformations. Nevertheless, poor stability of the species severely hinders its isolation, storage and operation, which is worse for nano-sized ones. We report here an unprecedented strategy to access to ultrastable copper-hydride nanoclusters (NCs), namely, using bidentate N-heterocyclic carbenes as stabilizing ligands in addition to thiolates. In this work, a simple synthetic protocol was developed to synthesize the first large copper-hydride nanoclusters (NCs) stabilized by N-heterocyclic carbenes (NHCs). The NC, with the formula of Cu31(RS)25(NHC)3H6 (NHC = 1,4-bis(1-benzyl-1H-benzimidazol-1-ium-3-yl) butane, RS = 4-fluorothiophenol), was fully characterized by high resolution Fourier transform ion cyclotron resonance mass spectrum, nuclear magnetic resonance, ultra-violet visible spectroscopy, density functional theory (DFT) calculations and single-crystal X-ray crystallography. Structurally, the title cluster exhibits unprecedented Cu4 tetrahedron-based vertex-sharing (TBVS) superstructure (fusion of six Cu4 tetrahedra). Moreover, the ultrahigh thermal stability renders the cluster a model system to highlight the power of NHCs (even other carbenes) in controlling geometrical, electronic and surface structure of polyhydrido copper clusters.

BaGe8As14 - a semiconducting sodalite type compound

The new sodalite type compound BaGe8As14 was synthesized via solid-state reactions and structurally characterized with single crystal X-ray diffraction (space group I-43m). Vertex-sharing GeAs4-tetrahedra form the β-cages with additional Ge/As...

Synthesis and Crystal Structure of the Short LnSb2O4Br Series (Ln = Eu–Tb) and Luminescence Properties of Eu3+-Doped Samples

Pale yellow crystals of LnSb2O4Br (Ln = Eu–Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group P21/c. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III), in LnSb2O4Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the form of square hemiprisms. These [LnO8]13− polyhedra form layers parallel to (100) by sharing common edges. All antimony(III) cations are coordinated by three oxygen atoms forming ψ1-tetrahedral [SbO3]3− units, which have oxygen atoms in common building up meandering strands along [001] according to {[SbO2/2vO1/1t]–}∞1 (v = vertex-sharing, t = terminal). The bromide anions are located between two layers of these parallel running oxoantimonate(III) strands and have no bonding contacts with the Ln3+ cations. Since Sb3+ is known to be an efficient sensitizer for Ln3+ emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb2O4Br and TbSb2O4Br doped with about 1.0–1.5 at-% Eu3+ efficient sensitization of the Eu3+ emission could be detected. For TbSb2O4Br, in addition, a remarkably high energy transfer from Tb3+ to Eu3+ could be detected that leads to a substantially increased Eu3+ emission intensity, rendering it an efficient red light emitting material.

Jeankempite, Ca5(AsO4)2(AsO3OH)2(H2O)7, a new arsenate mineral from the Mohawk Mine, Keweenaw County, Michigan, USA

Jeankempite, Ca5(AsO4)2(AsO3OH)2(H2O)7, is a new mineral species (IMA2018-090) discovered amongst coatings of arsenate minerals on oxidised copper arsenides from the Mohawk No. 2 mine, Mohawk, Keweenaw County, Michigan, USA. The new mineral occurs as lamellar bundles of colourless to white plates up to 1 mm wide and is visually indistinguishable from guérinite, with which it forms intergrowths. Jeankempite is transparent to translucent with a waxy lustre and white streak, is non-fluorescent under longwave and shortwave ultraviolet illumination, has a Mohs hardness of ~1.5 and brittle tenacity with uneven fracture. Crystals are flattened on {01 $\bar{1}$ } and exhibit perfect cleavage on {01 $\bar{1}$ }. Optically, jeankempite is biaxial (+), α = 1.601(2), β = 1.607(2), γ = 1.619(2) (white light); 2Vmeas. = 72(2)° and 2Vcalc. = 71.0°. The empirical formula is (Ca4.97Na0.013Mg0.017)(As3.99S0.01)4O23H16, based on 23 O and 16 H atoms per formula unit. Thermogravimetric analysis indicates that jeankempite undergoes four weight losses totalling 16.82%, close to the expected loss of 16.30%, corresponding to eight H2O. Jeankempite is triclinic, P $\bar{1}$ , a = 6.710(6), b = 14.901(14), c = 15.940(15) Å, α = 73.583(12)°, β = 81.984(12)°, γ = 82.754(12)°, V = 1507(2) Å3 and Z = 3. The final structure was refined to R1 = 0.0591 for 2781 reflections with Iobs > 3σI. The crystal structure of jeankempite is built from a network of edge- and vertex-sharing CaO6, CaO7 and AsO4 polyhedra, and we hypothesise that the new mineral has formed due to a topotactic reaction brought on by dehydration of preexisting guérinite.

Rare Nuclearities in Ni(II) Cluster Chemistry: An Unprecedented {Ni12} Nanosized Cage from the Use of N-Naphthalidene-2-Amino-5-Chlorobenzoic Acid

The self-assembly reaction between NiI2, benzoic acid (PhCO2H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base triethylamine (NEt3), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear [Ni12I2(OH)6(O2CPh)5(nacb)5(H2O)4(MeCN)4]I (1) cluster compound in ~30% yield. Complex 1 has a cage-like conformation, comprising twelve distorted, octahedral NiII ions that are bridged by five μ3-OH−, one μ-OH−, an I− in 55% occupancy, five PhCO2− groups (under the η1:η1:μ, η1:η2:μ3 and η2:η2:μ4 modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb2− groups. The overall {Ni12} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni3} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH2 chelate, and a rare example of polynuclear NiII complex containing coordinating I− ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the NiII ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb2− chelate in the presence of NiII metal ions, and the ability of this ligand to adopt a variety of different bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties.

Cooperative Multi-Simplex Algorithm: An Innovation from Localization to Globalization

This study suggests a novel cooperative multi-simplex algorithm that generalizes a local search optimizer to design a novel global search heuristic algorithm. The proposed algorithm exploits the vertex sharing strategy to enhance the search abilities of the working simplexes. The vertex sharing among the simplexes is carried out through cooperative step that is based on fitness of the underlying simplex. The proposed algorithm is applied to solve some systems of nonlinear equations by transforming them to optimization problems. Comparative analysis of results shows that the proposed method is practical and effective.

New Tetragonal ReGa5(M) (M = Sn, Pb, Bi) Single Crystals Grown from Delicate Electrons Changing

Single crystals of the new Ga-rich phases ReGa~5(Sn), ReGa~5(Pb) and ReGa~5(Bi) were successfully obtained from the flux method. The new tetragonal phases crystallize in the space group P4/mnc (No. 128) with vertex-sharing capped Re2@Ga14 oblong chains. Vacancies were discovered on the Ga4 and Ga5 sites, which can be understood as the direct inclusion of elemental Sn, Pb and Bi into the structure. Heat capacity measurements were performed on all three compounds resulting in a small anomaly which resembles the superconductivity transition temperature from the impurity ReGa5 phase. The three compounds were not superconducting above 1.85 K. Subsequently, electronic structure calculations revealed a high density of states around the Fermi level, as well as non-bonding interactions that likely indicate the stability of these new phases.

Synthesis and crystal structure of a series of stoichiometric (n)-ITB molybdenum-bronze oxides containing trivalent arsenic

A series of six new single crystals of fully stoichiometric As3+-bearing Mo-oxides and partially W-substituted Mo-oxides with formula AsmO(Mo1−xWxO3)p (m = 1, 2; p = 5, 7, 9, 10 and 11 and 0 ≤ x ≤ 0.6) was successfully grown using vapor-phase transport in vacuo. The crystal structures were determined using single-crystal X-ray diffraction data. All these compounds exhibit acentric orthorhombic symmetry with Z = 2, and belong to the so-called (n)-ITB (intergrowth tungsten bronzes) family, with n = 2, 3, 4 and 5. The six (n)-ITB phases have the following formulae: (2)-AsMo5O16 (Pm 2a), (2)-As2Mo10O31 (Pma 2), (3)-AsMo7O22 (Pmn 21), (3)-As(Mo5.53W1.47)O22 (Pmn 21), (4)-As(Mo4.33W4.67)O28 (Pm 2a) and (5)-As(W6.63Mo4.37)O34 (Pmn 21). Their structures consist of vertex-sharing MO6 octahedral units (with M either Mo or Mo/W) connected so as to form three-dimensional frameworks. Such frameworks consist of perovskite tungsten bronzes (PTB) type slabs, from 2- to 5-octahedra wide, intergrown with single hexagonal tungsten bronzes (HTB) type slabs, stacked up to form pseudo-hexagonal tunnels along the a-axis. As3+ and additional oxygen atoms are located in off-center positions inside the tunnels, forming As–O bonds with peculiar arrangements. In particular, we obtained the first examples of structures where, besides the usual AsO3E distorted pyramidal geometry, As3+ adopts AsO4E coordination with a seesaw configuration.

The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2AMnTe3 (A=K, Rb), and NaCsMnTe2

A series of new sodium and mixed Na/A (A = K, Rb, Cs) tellurido manganates have been synthesized from melts of the pure elements (or MnTe) at maximum temperatures of 600–1000°C. The monoclinic crystal structures of the two pure sodium salts Na2Mn2Te3 (space group C2/c, a = 1653.68(2), b = 1482.57(2), c = 773.620(10) pm, β = 117.52°, Z = 8, R1 = 0.0225) and Na2Mn3Te4 (space group C2/m, a = 1701.99(3), b = 438.741(8), c = 691.226(12) pm, β = 90.3171(8)°, Z = 2, R1 = 0.0270) are both based on a hexagonal close packed Te2− arrangement. Na2Mn2Te3 is isotypic with Na2Mn2S3 and Na2Mn2Se3 and contains layers of [MnTe4] tetrahedra, which are connected via common edges to form tetramers [Mn4Te6]. These tetramers are further connected via μ3-Te atoms. Na2Mn3Te4 crystallizes in a new structure type, recently also reported for the selenido salt Na2Mn3Se4. Mn(2) forms ribbons of vertex-sharing dinuclear units $_\infty ^1[{\rm{T}}{{\rm{e}}_{2/2}}{\rm{MnT}}{{\rm{e}}_2}{\rm{MnT}}{{\rm{e}}_{2/2}}]$ running along the short b axis of the monoclinic cell. The Te atoms of these ribbons are also the ligands of edge-sharing [Mn(1)Te6] chains of octahedra. Similar to Na2Mn2Te3, the Na+ cations are octahedrally coordinated and the cations occupy tetrahedral (Mn2+) and octahedral (Na+, Mn2+) voids in the close Te2− packing. The isotypic K/Rb salts Na2AMnTe3 crystallize in a new structure type (orthorhombic, space group Pmc21, a = 1069.70(4)/1064.34(2), b = 1350.24(5)/1350.47(3), c = 1238.82(4)/1236.94(3) pm, Z = 4, R1 = 0.0445/0.0210). In contrast to the simple formula indicating a Mn(III) compound, the complex structure contains one layer consisting of undulated chains of edge-sharing tetrahedra $_\infty ^1[{\rm{M}}{{\rm{n}}^{{\rm{II}}}}{\rm{T}}{{\rm{e}}_{4/2}}]$ separated by free ditelluride dumbbells [Te2]2− and a second layer containing a complex chain of edge- and vertex-sharing [MnIITe4] tetrahedra, in which Mn(II) is coordinated to μ1- and μ2-Te2− ligands and an η1-ditellurido ligand. The cesium salt NaCsMnTe2 (orthorhombic, space group Cccm, a = 694.21(2), b = 1536.57(4), c = 664.47(2) pm, Z = 4, R1 = 0.0131) likewise forms a new structure type, which is an ordered superstructure of ThCr2Si2. Linear chains $_\infty ^1[{\rm{MnT}}{{\rm{e}}_{4/2}}]$ of edge-sharing tetrahedra are connected with similar chains $_\infty ^1[{\rm{NaT}}{{\rm{e}}_{4/2}}]$ to form [NaMnTe2] layers. The larger alkali cations Cs+ between the layers exhibit a cubic (CN = 8) coordination.