Neutron diffraction, specific heat and magnetic susceptibility of Ni3(PO4)2

The Ni₃(PO₄)₂ phosphate was synthesized by the ceramic method in air atmosphere. The crystal structure consists of a three-dimensional skeleton constructed from Ni₃O₁₄ edge-sharing octahedra, which are interconnected by (PO₄)³⁻ oxoanions with tetrahedral geometry. The magnetic behavior was studied on powdered sample by using susceptibility, specific heat and neutron diffraction data. The nickel(II) orthophosphate exhibits a three-dimensional magnetic ordering at approximately 17.1 K. However, its complex crystal structure hampers any parametrization of the J-exchange parameter. The specific heat measurements of Ni₃(PO₄)₂ exhibit a three-dimensional magnetic ordering (λ-type) peak at 17.1 K. Measurements above T_N suggest the presence of a small short-range order in this phase. The total magnetic entropy was found to be 28.1 KJ/mol at 50 K. The magnetic structure of the nickel(II) phosphate exhibits ferromagnetic interactions inside the Ni₃O₁₄ trimers which are antiferromagnetically coupled between them, giving rise to a purely antiferromagnetic structure.     

The first non-acetato members of the bis(anion)octacarboxylatotetrakis{di-2-pyridyl-methanediolate(−2)}enneametal(II) family of complexes: Synthesis, X-ray structures and magnetism of [M9(N3)2(O2CCMe3)8{(py)2CO2}4] (M = Co, Ni)

The combined use of di-2-pyridyl ketone [(py)₂CO] and azides (N₃⁻) in nickel(II) and cobalt(II) pivalate chemistry has afforded complexes [Ni₉(N₃)₂(O₂CCMe₃)₈{(py)₂CO₂}₄] (1) and [Co₉(N₃)₂(O₂CCMe₃)₈{(py)₂CO₂}₄] (2), where (py)₂CO₂²⁻ is the gem-diolate(−2) form of (py)₂CO. The complexes are isostructural and crystallize in the monoclinic P2₁/c space group. Their molecular structures consist of nine metal(II) ions, eight of which are arranged as two parallel squares flanking the ninth. DC magnetic susceptometry on powdered samples of 1 (1-p) reveal an overall antiferromagnetic behavior, leading to an S = 0 ground state. AC susceptometry reveals out-of-phase signals between 10 and 27 K, and ZFC and FC experiments show a divergence of the two curves below ∼27 K. Magnetization-decay and field-sweep experiments verify the relaxation behavior of the sample. Samples of the complex arising from carefully washed single crystals (1-cr) reveal a similar DC behavior, without however the appearance of cusps in the χ_ΜΤ versus T curves, and no relaxation. The relaxation behavior has been assigned to NiO impurities. The results illustrate the extreme care that should be taken when examining the magnetic properties of apparently analytically pure materials obtained under heating. Complex 2 exhibits an overall antiferromagnetic behavior, without observation of any relaxation phenomena.     

Studies on magnetic and calorimetric properties of double perovskites Ba2HoRuO6 and Ba2HoIrO6

Magnetic properties of double perovskite compounds Ba₂HoRuO₆ and Ba₂HoIrO₆ have been reported. Powder X-ray and neutron diffraction measurements show that these compounds have a cubic perovskite-type structure with the space group and the 1:1 ordered arrangement of Ho³⁺ and Ru⁵⁺ (or Ir⁵⁺) over the 6-coordinate B sites. Results of the magnetic susceptibility and specific heat measurements show that Ba₂HoRuO₆ exhibits two magnetic anomalies at 22 and 50 K. Analysis of the temperature dependence of magnetic specific heat indicates that the anomaly at 50 K is due to the antiferromagnetic ordering of Ru⁵⁺ ions and that the anomaly at 22 K is ascribable to the magnetic interaction between Ho³⁺ ions. Neutron diffraction data collected at 10 and 35 K show that the Ba₂HoRuO₆ has a long range antiferromagnetic ordering involving both Ho³⁺ and Ru⁵⁺ ions. Each of their magnetic moments orders in a Type I arrangement and these magnetic moments are anti-parallel in the ab-plane with each other. The magnetic moments are aligned along the c-direction. On the other hand, Ba₂HoIrO₆ is paramagnetic down to 1.8 K.     

Synthesis,crystal structure and magnetic properties of the helical oxalate-bridged copper(II) chain {[(CH3)4N]2[Cu(C2O4)2] · H2O}n

The preparation, crystal structure and magnetic properties of a new oxalate-containing copper(II) chain of formula {[(CH₃)₄N]₂[Cu(C₂O₄)₂] · H₂O}_n (1) [(CH₃)₄N⁺ = tetramethylammonium cation] are reported. The structure of 1 consists of anionic oxalate-bridged copper(II) chains, tetramethylammoniun cations and crystallization water molecules. Each copper(II) ion in 1 is surrounded by three oxalate ligands, one being bidentate and the other two exhibiting bis-bidenate coordination modes. Although all the tris-chelated copper(II) units from a given chain exhibit the same helicity, adjacent chains have opposite helicities and then an achiral structure results. Variable-temperature magnetic susceptibility measurements of 1 show the occurrence of a weak ferromagnetic interaction through the oxalate bridge [J = +1.14(1) cm⁻¹, the Hamiltonian being defined as H = –J ∑_nmS_i · S_j]. This value is analyzed and discussed in the light of available magneto-structural data for oxalate-bridged copper(II) complexes with the same out-of-plane exchange pathway.     

Ferromagnetic exchange coupling in phosphonato-bridged dinuclear copper(II) compound with monoethyl (pyridyn-2-ylmethyl)phosphonate ligand (2-mpmpe): Cu2(2-mpmpe)2(H2O)2(NO3)2

The interaction of diethyl (pyridyn-2-ylmethyl)phosphonate (2-pmpe) with Cu(NO₃)₂ · 6H₂O leads to a partial hydrolysis of the starting ligand and formation of the compound of the formula Cu₂(2-mpmpe)₂(H₂O)₂(NO₃)₂, where 2-mpmpe = monoethyl (pyridyn-2-ylmethyl)phosphonate. The crystal and molecular structure of a copper(II) compound was determined by single X-ray diffraction method. Its structure consists of five-coordinated in distorted square planar geometry (CuNO₄ chromophore) copper(II) ions doubly bridged by OPO from phosphonate. The Cu?Cu distance is 4.69 Å. The crystal packing is determined by the interdinuclear hydrogen bond system, which leads to a three-dimensional (3D) H-bonds network. The compound was characterized by infrared, ligand field, EPR spectroscopy, and magnetic studies. The magnetic properties of the title compound investigated over the 1.8–300 K, revealed the occurrence of a weak ferromagnetic coupling through phosphonate bridge (J = 1.86 cm⁻¹) and interdimer superexchange coupling through H-bond network (zJ′ = −0.17 cm⁻¹). Spectroscopic and magnetic properties are presented in the light of crystal structure.     

Isolated spin 3/2 plaquettes in Na3RuO4

The crystal structure of Na₃RuO₄ determined by powder neutron diffraction is reported. The structure consists of isolated tetramers of edge sharing RuO₆ octahedra in the ab plane, creating isolated four-member plaquettes of Ru atoms comprised of two equilateral triangles sharing an edge. Magnetic susceptibility measurements reveal an antiferromagnetic transition at ∼29 K, with . Neutron diffraction data indicate the onset of three-dimensional magnetic ordering at 29 K.     

Long-range magnetic ordering of S=1/2 linear trimers in A3Cu3(PO4)4 (A=Ca, Sr, and Pb)

Magnetic properties of S=1/2 linear trimer cluster compounds A₃Cu₃(PO₄)₄ (A=Ca, Sr, and Pb) were investigated. Magnetic susceptibility data for the three compounds showed that paramagnetic copper spins form trimers with the total spin of 1/2 below about 45 K. Specific heat and magnetization measurements indicated that the trimer clusters undergo ferromagnetic long-range ordering at for A=Ca and antiferromagnetic long-range ordering at for A=Sr and for A=Pb. A₃Cu₃(PO₄)₄ exhibited 1/3-magnetization plateau at least up to magnetic field of 55 T at 1.3 and 4.2 K. A₃Cu₃(PO₄)₄ with A=Sr and Pb showed a spin-flop transition near 0.03 T in the antiferromagnetic state at 0.08 K. Specific heat data at magnetic fields clearly showed broad maxima at low temperatures due to the finite intra-chain interaction in one-dimensional arrays of the trimers.     

Layered hybrid organic-inorganic Co(II) alkylphosphonates. Synthesis, crystal structure and magnetism of the first two members of the series: Co[(CH3PO3)(H2O)] and Co[(C2H5PO3)(H2O)]

Co[(CH₃PO₃)(H₂O)] (1) and Co[(C₂H₅PO₃)(H₂O)] (2) were prepared by the hydrothermal method and isolated as blue-violet platelet crystals. They were characterized by X-ray diffraction, FT-IR, TGA-DSC techniques and their magnetic properties studied by a dc-SQUID magnetometer. Compound (1) shows an hybrid layered structure, made of alternating inorganic and organic layers along the a-direction of the unit cell. The inorganic layers contain Co(II) ions six-coordinated by five phosphonate oxygen atoms and one from the water molecule. These layers are separated by bi-layers of methyl groups and van der Waals contacts are established between them. In compound (2), the layered hybrid structure is rather similar to that described for compound (1), but the alternation of the inorganic and organic layers is along the b-direction of the unit cell. The magnetic behavior of (1) and (2) as function of temperature and magnetic field was studied. The compounds obey the Curie-Weiss law at temperatures above 100 K, the Curie C, and Weiss θ constants for the methyl derivative being and and for the ethyl derivative and , respectively. The observed magnetic moments for Co atom at room temperature (i.e. μ_eff=5.18 and 5.38 BM, respectively) are higher than those expected for a spin-only value for high spin Co(II) (S=3/2), revealing a substantial orbital contribution to the magnetic moment. The negative values of θ are an indication of the presence of antiferromagnetic exchange couplings between the near-neighbors Co(II) ions, within the layers. [Co(C_nH_2n+1PO₃)(H₂O)] (n=1,2) are 2D Ising antiferromagnets at low temperatures.     

Magnetostructural correlations in the antiferromagnetic Co2−x Cux(OH)AsO4 (x=0 and 0.3) phases

The Co_2−xCu_x(OH)AsO₄ (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2) Å, b=8.559(2) Å, c=6.039(1) Å and a=8.316(1) Å, b=8.523(2) Å, c=6.047(1) Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O₅-trigonal bipyramid dimers and M(2)O₆-octahedral chains (M=Co and Cu) are present. Co₂(OH)AsO₄ shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21 K within the presence of a ferromagnetic component below the ordering temperature. When Co²⁺ is partially substituted by Cu²⁺ions, Co_1.7Cu_0.3(OH)AsO₄, the ferromagnetic component observed in Co₂(OH)AsO₄ disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx²−y² orbital and the absence of overlap between neighbour ions.     

New stable germylenes, stannylenes, and related compounds. 5. Germanium(II) and tin(II) azides [N3-E-OCH2CH2NMe2]2 (E = Ge, Sn): synthesis and structure

New stable azido derivatives of divalent germanium and tin [N₃-E¹⁴-OCH₂CH₂NMe₂]₂ (E¹⁴ = Ge (1), Sn (2)) have been synthesized by use of the β-dimethylaminoethoxy ligand that forms the intramolecular E¹⁴ ← N coordination bond. Their crystal structures have been determined by X-ray diffraction analysis. Compounds 1 and 2 are centrosymmetric dimers via two intermolecular dative E¹⁴ ← O interactions with essentially linear monodentate azide ligands. The dominant canonical form of the E¹⁴-azide moieties is E¹⁴-N-NN.     

Syntheses and X-ray crystallographic studies of {[Ni(en)2(pot)2]0.5CHCl3} and [Ni(en)2](3-pytol)2

Two novel Ni(II) complexes {[Ni(en)₂(pot)₂]0.5CHCl₃} (3) {pot = 5-phenyl-1,3,4-oxadiazole-2-thione} (1) and [Ni(en)₂](3-pytol)₂ (4) {3-pytol = 5-(3-pyridyl)-1,3,4-oxadiazole-2-thiol} (2) have been synthesized using en as coligand. The metal complexes have been characterized by physical and analytical techniques and also by single crystal X-ray studies. The complexes 3 and 4 crystallize in monoclinic system with space group P21/a and P121/c, respectively. The complex 3 has a slightly distorted octahedral geometry with trans (pot)⁻ ligands while 4 has a square planar geometry around the centrosymmetric Ni(II) center with ionically linked trans (3-pytol)⁻ ligands. The π?π (face to face) interaction plays an important role along with hydrogen bondings to form supramolecular architecture in both complexes.     

Relations of crystal structure to magnetic properties in the quasi-one-dimensional compound PbNi1.88Mg0.12V2O8

The crystal structure of the quasi-one-dimensional oxide PbNi_1.88Mg_0.12V₂O₈ has been studied by Rietveld analysis of combined high-resolution neutron and X-ray powder diffraction data at 300 K and at low temperatures. The (Ni/Mg)O₆ octahedral units share a common edge and form spiral chains along the c-axis of the tetragonal unit cell, without deviating the I4₁cd (Z=8) symmetry upon cooling. DC magnetic susceptibility measurements show that the system undergoes a magnetic phase transition below T_N≅3.4 K. Rietveld analysis of the medium resolution neutron powder diffraction data confirms that impurity-induced antiferromagnetic order (with propagation vector, ) takes over from the Haldane ground state of the parent compound. The power-law [β=0.31(3)] temperature evolution of the strongest magnetic Bragg peak intensity indicates three-dimensional Ising-type magnetic interactions, while the reduced magnitude of the Ni²⁺ moment [〈μ〉=0.98(3) μ_B] suggests important zero-point spin fluctuations. Structural considerations are consistent with small changes in the interatomic distances around the bridging tetrahedral VO₄ entities separating the chains. However, no bulk structural phase transition concurrent to the Néel ordering is found. We show that the modification of intra- and inter-chain Ni-Ni distances upon cooling promotes the magnetic coupling of the end-of-chain liberated S=1/2 spins and leads to antiferromagnetic ordering.     

Syntheses and study on nickel and copper complexes with 1,3,5-benzenetricarboxylic acid. Crystal and molecular structure of [Cu3(mdpta)3(btc)](ClO4)3 · 4H2O

Nickel and copper complexes containing 1,3,5-benzenetricarboxylic acid, with a combination of selected N-donor ligands and Schiff bases, of the composition Ni₃(bimz)₆(btc)₂ · 12H₂O (1), Ni₃(btz)₉(btc)₂ · 12H₂O (2), Ni₂(L₁)(btc) · 7H₂O (3), Ni₃(L₂)₂(Hbtc) · 9H₂O (4), Ni₂(L₃)(btc) · 4H₂O (5), Cu₂(L₄)(btc) · 7H₂O (6), [Cu₃(pmdien)₃(btc)](ClO₄)₃ · 6H₂O (7) and [Cu₃(mdpta)₃(btc)](ClO₄)₃ · 4H₂O (8); H₃btc = 1,3,5-benzenetricarboxylic acid, bimz = benzimidazole, btz = 1,2,3-benztriazole, L₁ = 2-[(phenylimino)methyl]phenol, L₂ = N,N′-bis-(salicylidene)propylenediamine, L₃ = 2-{[(2-nitrophenyl)methylene]amino}phenol, L₄ = 2-[(4-methoxy-phenylimino)methyl]phenol, pmdien = N,N,N′,N″,N″-pentamethyldiethylenetriamine, mdpta = N,N-bis-(3-aminopropyl)methylamine, have been synthesized. The complexes have been studied by elemental analysis, IR, UV–Vis spectroscopies, magnetochemical and conductivity measurements and selected compounds also by thermal analysis. The crystal and molecular structure of complex 8 was solved. The complex is trinuclear with btc³⁻-bridge. The coordination polyhedron around each copper atom can be described as a distorted square with a CuON₃ chromophore formed by one oxygen atom of carboxylate and three nitrogen atoms of mdpta. The magnetic properties of 8 have been studied in the 1.8–300 K temperature range revealing a very weak antiferromagnetic exchange interaction with J = −0.56 cm⁻¹ for g = 2.13(9). The antimicrobial activities against selected strains of bacteria were evaluated. It was found that only complex 5 is able to inhibit the growth of Staphylococcus strains.     

New stable germylenes, stannylenes, and related compounds: 6. Heteroleptic germanium(II) and tin(II) compounds [(SiMe3)2N-E-OCH2CH2NMe2]n (E = Ge, n = 1; Sn, n = 2): synthesis and structure

New stable heteroleptic germanium(II) and tin(II) compounds [(SiMe₃)₂N-E¹⁴-OCH₂CH₂NMe₂]_n (E¹⁴ = Ge, n = 1 (1), Sn, n = 2 (2)) have been synthesized and their crystal structures have been determined by X-ray diffraction analysis. While compound 1 is monomer stabilized by intramolecular Ge ← N coordination, compound 2 is associated to dimer via intermolecular dative Sn ← O interactions.     

Specific heat and neutron diffraction study on quaternary sulfides BaNd2CoS5 and BaNd2ZnS5

Magnetic and electrical properties are investigated for quaternary neodymium sulfides BaNd₂TS₅ (T=Co, Zn) through the specific heat, neutron diffraction, and electrical conductivity measurements. Their electrical conductivities show semiconductive behavior, which follows the Arrhenius temperature dependence with the activation energy of E_a=1.46 eV for BaNd₂ZnS₅ and E_a=1.19 eV for BaNd₂CoS₅. The specific heat of BaNd₂ZnS₅ has a λ-type anomaly at 2.8 K due to the antiferromagnetic ordering of the Nd³⁺ moments and a Schottky-type anomaly at around 60 K, which results from the crystal field splitting of the ⁴I_9/2 ground state of the Nd³⁺ ion. The specific heat of BaNd₂CoS₅ shows two λ-type anomalies at 5.7 K due to the antiferromagnetic ordering of Nd³⁺ and at 58 K due to the antiferromagnetic ordering of Co²⁺. The latter overlaps with the Schottky-type anomaly due to the crystal field splitting of the Nd³⁺ ion. Neutron diffraction measurements for BaNd₂CoS₅ show that a magnetic arrangement of the Co²⁺ moments has a collinear antiferromagnetic structure, while that of the Nd³⁺ moments has a noncollinear one.     

Anomalous low-temperature behavior of the Co dimers in the oxo-halide CoSb2O3Br2

We report the synthesis, crystal structure determination, magnetic and low-temperature structural properties of a new cobalt antimony oxo-bromide. CoSb₂O₃Br₂ crystallizes in the triclinic crystal system, space group P−1, with the following lattice parameters: a=5.306(3) Å, b=7.812(4) Å, c=8.0626(10) Å, α=88.54(3)°, β=82.17(3)°, γ=80.32(4)°, and Z=2. The crystal structure was solved from single crystal X-ray data and refined on F², R₁=3.08. The structure consists of layers made up by three building blocks, [CoO₄Br₂], [SbO₃Br], and [SbO₃] that are connected via edge- and corner-sharing so that structural Co-Co dimers are formed. The layers have no net charge and are only weakly connected by van der Waals forces to adjacent layers. Above ∼25 K the magnetic susceptibility is independent of the magnetic field and can be very well described by a Curie-Weiss law. Below 25 K the susceptibility passes through a maximum and decreases again that is typical for the onset of long-range antiferromagnetic correlations. Long-range antiferromagnetic ordering is observed below T_N∼9 K indicating substantial inter-dimer exchange coupling between Co-Co dimers within the layers. However, according to the heat capacity results only a minute fraction of the entropy is associated with the long-range ordering transition. The phonon anomalies observed for T<6 K in Raman scattering and an anomaly in the specific heat point to a structural instability leading to a loss of inversion symmetry at lowest temperatures.     

A new three-dimensional cobalt phosphate: Co5(OH2)4(HPO4)2(PO4)2

A three-dimensional (3D) cobalt phosphate: Co₅(OH₂)₄(HPO₄)₂(PO₄)₂ (1), has been synthesized by hydrothermal reaction and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic techniques. The title compound is a template free cobalt phosphate. Compound 1 exhibits a complex net architecture based on edge- and corner-sharing of CoO₆ and PO₄ polyhedra. The magnetic susceptibility measurements indicated that the title compound obeys Curie-Weiss behavior down to a temperature of 17 K at which an antiferromagnetic phase transition occurs.     

New cationic palladium (II) and rhodium (I) complexes of [Ph2PCH2C(Ph)N(2,6-Me2C6H3)]

Treatment of the bulky iminophosphine ligand [Ph₂PCH₂C(Ph)N(2,6-Me₂C₆H₃)] (L) with [M(CH₃CN)₂(ligand)]⁺ⁿ, where for M = Pd(II): ligand = η³-allyl, n = 1, and for M = Rh(I), ligand: 2(C₂H₄), 2(CO) or cod, n = 0, yields the mono-cationic iminophosphine complexes [Pd(η³-C₃H₅)(L)][BF₄] (1), [Rh(cod)(L)][BF₄] (2), [Rh(CO)(CH₃CN)(L)][BF₄] (3), and cis-[Rh(L)₂][BF₄] (4). All the new complexes have been characterised by NMR spectroscopy and X-ray diffraction. Complex 1 shows moderate activity in the copolymerisation of CO and ethene but is inactive towards Heck coupling of 4-bromoacetophenone and n-butyl acrylate.     

Metal phosphonates containing pyridyl N-oxide groups: Syntheses of Cd{(2-C5H4NO)CH(OH)PO3}(H2O)2 and Zn{(4-C5H4NO)CH(OH)PO3} with chain and layer structures

This paper reports the syntheses and characterization of two phosphonate compounds Cd{(2-C₅H₄NO)CH(OH)PO₃}(H₂O)₂ (1) and Zn{(4-C₅H₄NO)CH(OH)PO₃} (2) based on hydroxy(2-pyridyl N-oxide)methylphosphonic and hydroxy(4-pyridyl N-oxide)methylphosphonic acids. Compound 1 has a chain structure in which dimers of edge-shared {CdO₆} octahedra are linked by {CPO₃} tetrahedra through corner-sharing. The pyridyl rings reside on the two sides of the inorganic chain. Compound 2 has a layer structure where the inorganic chains made up of corner-sharing {ZnO₄} and {CPO₃} tetrahedra are covalently connected by pyridyl N-oxide groups. Crystal data for 1: triclinic, space group , a=6.834(1) Å, b=7.539(1) Å, c=10.595(2) Å, α=84.628(3)°, β=74.975(4)°, γ=69.953(4)°. For 2: triclinic, space group , a=5.219(1) Å, b=8.808(2) Å, c=9.270(2) Å, α=105.618(5)°, β=95.179(4)°, γ=94.699(4)°.