K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

Microporous framework polar silicate-germanates with a wide isomorphic substitution: (K2.9Cs0.1)(Sc0.7In0.3)[(Si2.95Ge0.05)O9]·H2O and (K2.16Cs0.84)Bi[(Si1.5Ge1.5)O9]·H2O

New silicate-germanates (K2.9Cs0.1)(Sc0.7In0.3)[(Si2.95Ge0.05)O9]·H2O and (K2.16Cs0.84)Bi[(Si0.5Ge0.5)3O9]·H2O have been synthesized in multi-component systems under mild hydrothermal conditions. The new compounds are classified as new representatives of close related K3ScSi3O9·H2O parent structure, sp. gr. Pmn21. Their structural and isomorphic peculiarities are compared with it as well as with earlier investigated K1.46Pb1.54Сa[(Ge0.23Si0.77)3O9](ОН)0.54·0.46Н2О. Together with other known compounds, silicate-germanates form the extensive family A3M[T3O9]·H2O, A = K, Cs, Ca, Pb; M = Ho, Sc, Lu, Tb, Er, Y, Bi, Pb, In; T = Si, Ge, with a mixed microporous framework combined of M-octahedra and T-tetrahedra. Large alkali metal or/and Ca, Pb cations fill broad framework channels with cross-section up to 7.3 Å. Because of wide isomorphic substitution in the channels, and in tetrahedra and octahedra, ion exchange properties in the family are expected. Due to polar symmetry, all the crystals possess second-order nonlinearity which was confirmed with positive SHG tests for four compositions. Powder SHG experiments demonstrated moderate second harmonic intensities of order of α-quartz standard signals.

(Na,Li)3(Cl,OH)[Cu3OAl(PO4)3]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure

The synthesis and characterization of a first salt-inclusion aluminophosphate oxocuprate, (Na,Li)₃(Cl,OH)[Cu₃OAl(PO₄)₃], obtained as single crystals, is reported. A novel phase, with a strongly pseudo-orthorhombic structure, is described as a monoclinic crystal structure established by the study of a pseudomerohedric microtwin. It was investigated using scanning electron microscopy, microprobe analysis and low-temperature X-ray diffraction. The composite crystal structure represents an original framework assembled from Cu-centered polyhedra, AlO₆ octahedra and PO₄ tetrahedra with channels, which incorporate the Na/Li salt component [(Na,Li)₃(Cl,OH)]²⁺ that ensures electroneutrality of the compound. Layers of strongly corrugated chains of Cu-centered octahedra with shared edges and linked by PO₄ tetrahedra are shown to be topologically identical with the layers also built from Cu-centered polyhedra and AsO₄/VO₄ tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M_0.5Cl)[Cu₅O₂(AsO₄)(VO₄)] [Siidra et al. (2019). MinMag, 83, 847-853]. `Sawtooth chains' and pairs of Cu-centered octahedra inherent in the title structure may be of interest in solid-state physics, engaging studies in the field of low-dimensional and frustrated magnetism.

Novel first-row transition-metal phosphates: hydrothermal synthesis and crystal structures

Two new compounds, sodium copper nickel diorthophosphate, Na2CuNi(PO4)2 (I), and dimanganese copper diorthophosphate, Mn2Cu(PO4)2 (II), were synthesized hydrothermally, yielding single crystals, and were studied by X-ray diffraction. In the crystal structures, various transition metals of d-elements occupy symmetrically independent crystallographic positions with different coordination geometries. In the crystal structure of Na2NiCu(PO4)2, NiO6 and CuO6 octahedra share edges to form chains that PO4 groups link into a framework with cavities filled with Na atoms. Layered cationic fragments formed from dimers of MnO5 trigonal bipyramids and CuO4 square planes, sharing vertices, are connected through PO4 tetrahedra into a 3-periodic Mn2Cu(PO4)2 crystal structure. Structural correlations between Na2NiCu(PO4)2 and NaCuPO4 are discussed, and crystal–chemical details of the currently known exclusively synthetic mixed Mn/Cu and Ni/Cu phosphates are presented.

Nonstoichiometric Ellenbergerite-Type Phosphates: Hydrothermal Synthesis, Crystal Chemistry, and Magnetic Behavior

We synthesized single crystals of Na_0.55Ni₆(OH)₃(H_0.61PO₄)₄ (I) and polycrystals of (Na, Ni)_0.64Ni_5.68(OH)₃(H_0.67PO₄)₄ (II) with ellenbergerite-like structures using the hydrothermal method. The phases crystallize in the hexagonal space group P6₃mc with the following unit cell parameters: a = 12.5342(1) Å, c = 4.9470(1) Å, and V = 673.08(2) ų for I; a = 12.4708(2) Å, c = 4.9435(2) Å, and V = 665.82(2) ų for II; and Z = 2. Their crystal structures are based on a 3D framework built from NiO₆ octahedra and PO₄ tetrahedra. The difference between I and II lies in the way the structural channels are filled along the [001] direction. These channels accommodate segments of Na- and (Na, Ni)-centered chains of face-sharing octahedra in the structures I and II, respectively. The magnetic susceptibility χ and the specific heat C_p evidence pronounced low-dimensional magnetic behavior at elevated temperatures and the formation of the weakly ferromagnetic long-range order at T_N^I = 61 K and T_N^II = 63 K. Analysis of the χ(T) data within both chain and dimer spin models allows the estimation of the leading exchange interaction parameters in the compounds under study.

Sawtooth chains self-assembled from clusters of MnO6 octahedra within the silicate framework of K3Mn4Si10O24.33(H2O,OH)3/V,B

A disordered mineralogically probable silicate hydrate K3Mn4Si10O24.33(H2O,OH)3/V,B, obtained hydrothermally, demonstrates low-dimensional magnetic behavior.

Hydrothermal Synthesis and a Composite Crystal Structure of Na6Cu7BiO4(PO4)4[Cl,(OH)]3 as a Candidate for Quantum Spin Liquid

A novel sodium bismuth oxo-cuprate phosphate chloride, Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77], containing square-kagomé layers of Cu²⁺ has been synthesized by hydrothermal techniques. The compound crystallizes in the tetragonal space group P4/nmm, a = 10.0176(4), c = 10.8545(6), Z = 2, V = 1089.3(1) ų, R₁ = 0.021, wR = 0.053, S = 1.32. Its composite crystal structure includes [O₄Cu₆Bi]⁷⁺ layers, which are formed by the clusters of oxygen-centered tetrahedra [OCu₃Bi]. These positively charged two periodic fragments are intercalated in a negatively charged [CuNa₆Cl₃(PO₄)₄]^7- matrix built by Na-centered polyhedra, PO₄ tetrahedra, and CuO₄Cl pyramids. The composite character of the crystal structure of Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77], as well as the way of its self-assembly, are discussed in close connection with the sulfohalite Na₆ClF(SO₄)₂ salt. It is shown that the "host-guest" model of the formation of the tetragonal Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77] phase is due to the group-subgroup symmetry relation with the cubic crystal structure of mineral sulfohalite and is also supported by the crystallization condition in excess sodium chloride. The magnetic subsystem of Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77] is represented by a dense square-kagomé network of 2Cu1 and 4Cu2 ions, decorated with weakly bonded Cu3 ions. Measurements of magnetization and heat capacity indicate the absence of long-range order up to 2 K, which makes this compound a candidate for a highly demanded spin liquid.

An Orthorhombic Modification of KCoPO4 Stabilized under Hydrothermal Conditions: Crystal Chemistry and Magnetic Behavior

A novel modification of the KCoPO₄, δ-phase has been prepared by hydrothermal synthesis at 553 K. The compound crystallizes in the orthorhombic system with the unit-cell parameters a = 8.5031(8), b = 10.2830(5), c = 54.170(4) Å. The crystal structure was determined based on synchrotron low-temperature single-crystal X-ray diffraction data obtained from an inversion twin in the space group P2₁2₁2₁ and refined to R = 0.077 for 5156 reflections with I > 3σ(I). The δ-KCoPO₄ possesses a new structure type which is based on a framework built from sharing vertices Co- and P-centered tetrahedra. The {CoPO₄^-}_∞ construction of tetrahedra may be described as assembled from networks formed by two topologically diverse six-membered rings of tetrahedra stacked together through vertex-bridging contacts along the a axis. The ratio of the (UUUDDD) and (UUDUDD) rings, where (U) and (D) denote the orientation of the tetrahedra in the six-membered rings up and down relative to the plane grids, is equal to 5:1. The (UUDUDD) rings form bands parallel to the [010] direction each surrounded from both sides along the c axis by slabs of five ribbons width having alternative (UUUDDD) topology. Open in the [100] direction channels incorporate K⁺ ions; this structural feature permits to suppose ion-conductive and/or electrochemical properties of the title compound. The possible mechanism of the δ → γ phase transition is discussed on the basis of the crystal chemical analysis of the KCoPO₄ polymorphs. The title compound orders magnetically at T_N = 24.8 K.

Crystal structure and thermodynamic properties of dinickel diphosphate dihydrate Ni2(H2O)2[P2O7]

Single crystals of dinickel diphosphate dihydrate, Ni₂(H₂O)₂[P₂O₇], have been synthesized by a hydrothermal method. Its structure was refined in the monoclinic P2₁/n space group (unit cell parameters a = 6.2517(1) Å, b = 13.7892(3) Å, c = 7.2894(2) Å, β = 94.507(2)°, V = 626.45(2) ų, and Z = 4) based on low-temperature X-ray diffraction data until R- 0.016. Corrugated chains of NiO₅(H₂O) octahedra sharing edges are aligned in the [101[combining macron]] direction. They are linked into a three-dimensional framework through diphosphate groups and hydrogen bonds. A detailed crystal chemical analysis of the family Me₂(H₂O)₂[X₂O₇] revealed correlations between the unit-cell parameters of the isotypic transition metal phosphates and arsenates, their structural features and the sizes of structure forming cations. Despite the isolation of the cis and trans edge-sharing infinite zigzag chains of Ni-centered octahedra from each other no pronounced low dimensionality is seen in the magnetic response of Ni₂(H₂O)₂[P₂O₇]. The magnetic susceptibility χ evidences a short range correlation maximum at T_max = 11.9 K accompanied by the onset of long-range magnetic order at T_N = 9.4 K. Below T_N, the title compound exhibits the features of an archetype three-dimensional easy-axis antiferromagnet which experiences a sequence of spin-flop and spin-flip phase transitions. Basing on specific heat C_p and magnetization M studies, the magnetic phase diagram of Ni₂(H₂O)₂[P₂O₇] has been established.

Silicate-germanate K2Y[(Si3Ge)O10(OH)] with unusual complex corrugated layer and its correlation to ring silicate gerenite and chain silicate chkalovite

A new silicate-germanate K2Y[(Si3Ge)O10(OH)] was synthesized hydrothermally in a system Y2O3:GeO2:SiO2 = 1:1:2 (T = 280 °C; P = 90–100 atm.); K2CO3 was added to the solution as a mineralizer. Single-crystal X-ray diffraction experiment was carried out at low temperature (150 K). The unit cell parameters are a = 10.4975(4), b = 6.9567(2), c = 15.4001(6) Å, β = 104.894(4)°; V = 1086.86(7) Å3; space group is P 21/c. A novel complex anion is presented by corrugated (Si,Ge) tetrahedral layers connected by couples of YO6 octahedra into the mixed microporous framework with the channels along b and a axes, the maximal size of cross-section is ~5.6 Å. This structure has similarity with the two minerals: ring silicate gerenite (Ca,Na)2(Y,REE)3Si6O18 · 2H2O and chain silicate chkalovite Na2BeSi2O6. Six-member rings with 1̅ symmetry as in gerenite are distinguished in the new layer. They are mutually perpendicular to each other and connected by additional tetrahedra. Straight crossing chains in chkalovite change to zigzag four-link chains in the new silicate-germanate layer.

Rb2CaCu6(PO4)4O2, a novel oxophosphate with a shchurovskyite-type topology: synthesis, structure, magnetic properties and crystal chemistry of rubidium copper phosphates

Single crystals of Rb₂CaCu₆(PO₄)₄O₂ were synthesized by a hydrothermal method in the multicomponent system CuCl₂-Ca(OH)₂-RbCl-B₂O₃-Rb₃PO₄. The synthesis was carried out in the temperature range from 690 to 700 K and at the general pressure of 480-500 atm [1 atm = 101.325 kPa] from the mixture in the molar ratio 2CuO:CaO:Rb₂O:B₂O₃:P₂O₅. The crystals studied by single-crystal X-ray analysis were found to be monoclinic, space group C2, a = 16.8913 (4), b = 5.6406 (1), c = 8.3591 (3) Å, β = 93.919 (3)°, V = 794.57 (4) ų. The crystal structure of Rb₂CaCu₆(PO₄)₄O₂ is similar to that of shchurovskyite and dmisokolovite and is based upon a heteropolyhedral open framework formed by polar layers of copper polyhedra linked via isolated PO₄ tetrahedra. The presence of well-isolated 2D heteropolyhedral layers in the title compound suggests low-dimensional magnetic behavior which is masked, however, by the fierce competition between multiple ferromagnetic and antiferromagnetic exchange interactions. At T_C = 25 K, Rb₂CaCu₆(PO₄)₄O₂ reaches a magnetically ordered state with large residual magnetization.

Bi3(PO4)O3, the Simplest Bismuth(III) Oxophosphate: Synthesis, IR Spectroscopy, Crystal Structure, and Structural Complexity

The bismuth(III) oxophosphate Bi₃(PO₄)O₃ was obtained by hydrothermal synthesis. The unit cell has a = 5.6840(6) Å, b = 7.0334(7) Å, c = 9.1578(9) Å, α = 78.958(2)°, β = 77.858(2)°, γ = 68.992(2)°, V = 331.41(6) ų, space group P1̅, and Z = 2. The crystal chemical formula that reflects the presence of oxo-centered tetrahedra and triangles is ^2D[O^IIIO^IV₂Bi₃](PO₄). The crystal structure contains [O₃Bi₃]³⁺_∞∞-heteropolyhedral corrugated layers parallel to (001), which alternate along [001] with isolated (PO₄) tetrahedra. The structural complexity parameters are v = 22 atoms, I_G = 3.459 bits/atoms, and I_G,total = 76.107 bits/unit cell, and thus Bi₃(PO₄)O₃ is the simplest pure bismuth(III) oxophosphate.

[Radiofrequency ablation in comprehensive surgical treatment of patients with varicose veins of lower limbs]

Analysed herein are the results of using radiofrequency ablation (RFA) in comprehensive surgical treatment of patients presenting with varicose veins of the lower extremities. The study included a series of ninety-eight 28-to-60-year-old patients (with a total of 105 operations performed) suffering from varicose veins of the lower limbs. Of these, there were 10 men (10.3%) and 88 women (89.7%). Venous disease of clinical class C2 according to the CEAP classification was diagnosed in 80 patients, that of class C3 in 17, and that of class C4a in 1 patient. The procedure of RFA was performed by means of the VNUS device model RF62. The impact was exerted in an automatic mode, maintaining the catheter's temperature at 120° C during a 20-second treatment cycle for each 7 cm of the vein's length. In all cases, each 7-cm-long venous segment to be treated was acted upon 4 times. Forty-five patients after RFA underwent ultrasonographic monitoring performed first on POD 7 and then at 3, 6, 12 and 24 months. Recanalization of the trunk of the great saphenous vein (GSV) was registered in 3 (2.8%) cases at terms up to 3 months after the operation. In 2 cases recanalization turned out to be provoked by an incompetent perforant vein in the lower third of the femur. Seven (6.6%) patients with a large diameter of the great saphenous vein were found to develop post-closure hyperpigmentation which resolved spontaneously 8 months later. The remaining patients, with strict adherence to the indications for RFA, demonstrated complete obliteration of the vessel treated, with no recanalization observed ultrasonographically 10-12 months after the procedure. An additional experimental study with a morphological analysis confirmed appropriateness of carrying out four 20-second treatment cycles of RFA in each segment of the vein. A conclusion was made that RFA used in comprehensive surgical treatment for varicose veins of the lower limbs makes it possible to attain good therapeutic and cosmetic results that persist over time, if conducted in compliance with the mentioned fundamentally essential peculiarities of performing the procedure.

Crystal structure and spin-trimer magnetism of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2]

The novel borophosphate Rb_2.3(H₂O)_0.8Mn₃[B₄P₆O₂₄(O,OH)₂] was prepared under hydrothermal conditions at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F² to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) ų, and Z = 4. The title compound is the first example of a borophosphate with manganese ions adopting both octahedral and tetrahedral coordinations. Its unique crystal structure is formed by borophosphate slabs and chains of Mn²⁺-centered polyhedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb⁺ cations and water molecules. Topological relationships between borophosphates built from three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO₄ and HPO₄ tetrahedra, are discussed. The temperature dependence of the magnetic susceptibility of Rb_2.3(H₂O)_0.8Mn₃[B₄P₆O₂₄(O,OH)₂] reveals predominant antiferromagnetic exchange interactions and the high-temperature effective magnetic moment corresponding to the high-spin S = 5/2 state of Mn²⁺ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. A spin-trimer model with the leading exchange interaction J ∼ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations.

Structure-Property Relationships in α-, β'-, and γ-Modifications of Mn3(PO4)2

The manganese orthophosphate, Mn₃(PO₄)₂, is characterized by the rich variety of polymorphous modifications, α-, β'-, and γ-phases, crystallized in monoclinic P2₁/c (P2₁/n) space group type with unit cell volume ratios of 2:6:1. The crystal structures of these phases are constituted by three-dimensional framework of corner- and edge-sharing [MnO₅] and [MnO₆] polyhedra strengthened by [PO₄] tetrahedra. All compounds experience long-range antiferromagnetic order at Neel temperature T_N = 21.9 K (α-phase), 12.3 K (β'-phase), and 13.3 K (γ-phase). Additionally, second magnetic phase transition takes place at T* = 10.3 K in β'-phase. The magnetization curves of α- and β'-modifications evidence spin-floplike features at B = 1.9 and 3.7 T, while the γ-Mn₃(PO₄)₂ stands out for an extended one-third magnetization plateau stabilized in the range of magnetic field B = 7.5-23.5 T. The first-principles calculations define the main paths of superexchange interaction between Mn spins in these polymorphs. The spin model for α-phase is found to be characterized by collection of uniform and alternating chains, which are coupled in all three directions. The strongest magnetic exchange interaction in γ-phase emphasizes the trimer units, which make chains that are in turn weakly coupled to each other. The spin model of β'-phase turns out to be more complex compared to α- or γ-phase. It shows complex chain structures involving exchange interactions between Mn2 (Mn2', Mn2″) and Mn3 (Mn3', Mn3″). These chains interact through exchanges involving Mn1 (Mn1', Mn1″) spins.

[CLINICAL EFFICACY AND SAFETY OF LITHOLYTIC THERAPY WITH LIVODEXA IN PATIENTS WITH CHRONIC CHOLECYSTITIS AND BILIARY SLUDGE]

The authors present their own experience litholytic therapy of 68 patients with chronic cholecystitis and biliary sludge using the Livodexa (Sun Pharmaceutical Industries Ltd, India) at 12 and 24-week course of treatment. In a prospective 24-week investigation was estimated decrease in biliary sludge in the gallbladder as an integral indicator of the effective ness of litholytic therapy and decline of adverse event during treatment, as an indicator of the safety of treatment.

[The prognostic significance of cholesterol determination in the high-density lipoprotein fraction of blood donors]

The relationships between concentrations of HDLP cholesterol and total cholesterol (TC), triglycerides in the blood serum; between HDLP cholesterol content and TC have been analyzed in the group of blood donors. Three variants were determined: 1) high TC, normal HDLP cholesterol, low HDLP proportion in TC 2) high TC, high HDLP cholesterol, normal HDLP/TC 3) normal TC, low HDLP cholesterol, low proportion of HDLP in TC. There were no correlations between HDLP cholesterol and triglycerides quantities in the blood serum.

[Photoluminescence band and anti-Stokes emission of native collagen in the visible range of the spectrum]

Photoluminescence (PL) of collagen, phenylalanine and tyrosine has been experimentally studied in the range of 400-700 nm. Anti-Stokes emission was observed when PL was excited by visible light. Possible participation of an excimer in generation of PL was shown. It has been pointed out that phenylalanine chromophore plays a dominant role in fluorescence generation of collagen in the spectrum visible range.