The antiferromagnetic structures of the layered oxychalcogenides (Sr1−x Ba x )2CoO2Cu2S2 (0 ≤ x ≤ 1) have been determined by powder neutron diffraction. In these compounds Co2+ is coordinated by four ...oxide ions in a square plane and two sulfide ions at the apexes of an extremely tetragonally elongated octahedron; the polyhedra share oxide vertexes. The magnetic reflections present in the diffraction patterns can in all cases be indexed using a √2a × √2a × c expansion of the nuclear cell, and nearest-neighbor Co2+ moments couple antiferromagnetically within the CoO2 planes. The ordered magnetic moment of Co2+ in Sr2CoO2Cu2S2 (x = 0) is 3.8(1) μB at 5 K, consistent with high-spin Co2+ ions carrying three unpaired electrons and with an additional significant unquenched orbital component. Exposure of this compound to moist air is shown to result in copper deficiency and a decrease in the size of the ordered moment to about 2.5 μB; there is a strong correlation between the size of the long-range ordered moment and the occupancy of the Cu site. Both the tetragonal elongation of the CoO4S2 polyhedron and the ordered moment in (Sr1−x Ba x )2CoO2Cu2S2 increase with increasing Ba content, and in Ba2CoO2Cu2S2, which has Co2+ in an environment that is close to purely square planar, the ordered moment of 4.5(1) μB at 5 K is over 0.7 μB larger than that in Sr2CoO2Cu2S2, so the unquenched orbital component in this case is even larger than that observed in octahedral Co2+ systems such as CoO. The experimental observations of antiferromagnetic ground states and the changes in properties resulting from replacement of Sr by Ba are supported by ab initio calculations on Sr2CoO2Cu2S2 and Ba2CoO2Cu2S2. The large orbital moments in these systems apparently result from spin−orbit mixing of the unequally populated d xz , d yz , and d z 2 orbitals, which are reckoned to be almost degenerate when the CoO4S2 polyhedron reaches its maximum elongation. The magnitudes of the ordered moments in high-spin Co2+ oxide, oxychalcogenide, and oxyhalide systems are shown to correlate well with the tetragonal elongation of the coordination environment. The large orbital moments lead to an apparently magnetostrictive distortion of the crystal structures below the Neél temperature, with the symmetry lowered from tetragonal I4/mmm to orthorhombic Immm and the size of the distortion correlating well with the size of the long-range ordered moment for all compositions and for temperature-dependent data gathered on Ba2CoO2Cu2S2.
An homologous series of layered oxysulfides Sr2MnO2Cu2 m - δS m +1 with metamagnetic properties is described. Sr2MnO2Cu2 - δS2 (m = 1), Sr2MnO2Cu4 - δS3 (m = 2) and Sr2MnO2Cu6 - δS4 (m = 3), consist ...of MnO2 sheets separated from antifluorite-type copper sulfide layers of variable thickness by Sr2+ ions. All three compounds show substantial and similar copper deficiencies (δ ≈ 0.5) in the copper sulfide layers, and single-crystal X-ray and powder neutron diffraction measurements show that the copper ions in the m = 2 and m = 3 compounds are crystallographically disordered, consistent with the possibility of high two-dimensional copper ion mobility. Magnetic susceptibility measurements show high-temperature Curie−Weiss behavior with magnetic moments consistent with high spin manganese ions which have been oxidized to the (2+δ)+ state in order to maintain a full Cu-3d/S-3p valence band, and the compounds are correspondingly p-type semiconductors with resistivities around 25 Ω cm at 295 K. Positive Weiss temperatures indicate net ferromagnetic interactions between moments. Accordingly, magnetic susceptibility measurements and low-temperature powder neutron diffraction measurements show that the moments within a MnO2 sheet couple ferromagnetically and that weaker antiferromagnetic coupling between sheets leads to A-type antiferromagnets in zero applied magnetic field. Sr2MnO2Cu5.5S4 and Sr2MnO2Cu3.5S3 are metamagnets which may be driven into the fully ordered ferromagnetic state below 25 K by the application of fields of 0.06 and 1.3 T respectively. The relationships between the compositions, structures, and physical properties of these compounds, and the prospects for chemical control of the properties, are discussed.
The alkaline earth silicon nitrides AESiN2 (AE = Ca, Sr, Ba) are reported, synthesized as clear, colorless, single crystals from molten sodium at 900−1100 °C or, in the cases of BaSiN2 and SrSiN2, as ...white powders by reacting powdered intermetallics AESi with flowing anhydrous ammonia at 550−1000 °C. Structures were determined from single-crystal X-ray diffraction measurements at 150 K: BaSiN2 crystallizes in space group Cmca (No. 64) with a = 5.6046(1) Å, b = 11.3605(3) Å, c = 7.5851(2) Å, and Z = 8. The structure consists of pairs of SiN4 tetrahedra edge-linked to form bow-tie-shaped Si2N6 dimers which share vertexes to form layers and has no analogue in oxide chemistry. SrSiN2 has a distorted form of this structure (SrSiN2: space group P21/c (No. 14), a = 5.9750(5) Å, b = 7.2826(7) Å, c = 5.4969(4) Å, β = 113.496(4)°, Z = 4). The structure of CaSiN2 contains only vertex-sharing SiN4 tetrahedra, linked to form a three-dimensional stuffed-cristobalite type framework isostructural with KGaO2 (CaSiN2: space group Pbca (No. 61), a = 5.1229(3) Å, b = 10.2074(6) Å, c = 14.8233(9) Å, Z = 16).
The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination ...environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) Å, b = 12.8541(7) Å, c = 6.1175(4) Å, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible.
The strontium gallium oxynitride Sr4GaN3O and nitride−carbodiimide Sr4GaN3(CN2) are reported, synthesized as single crystals from molten sodium at 900 °C. Red Sr4GaN3O crystallizes in space group ...Pbca (No. 61) with a = 7.4002(1) Å, b = 24.3378(5) Å, c = 7.4038(1) Å, and Z = 8, as determined from single-crystal X-ray diffraction measurements at 150 K. The structure may be viewed as consisting of slabs Sr4GaN32+ containing double layers of isolated GaN36- triangular anions arranged in a “herringbone” fashion, and these slabs are separated by O2- anions. Brown Sr4GaN3(CN2) has a closely related structure in which the oxide anions in the Sr4GaN3O structure are replaced by almost linear carbodiimide CN22- anions Sr4GaN3(CN2): space group P21/c (No. 14), a = 13.4778(2) Å, b = 7.4140(1) Å, c = 7.4440(1) Å, β = 98.233(1)°, and Z = 4.
Simple basic ingredients are at the origin of the synthesis of Na(OCP), the phosphorus analogue of sodium cyanate. Na(OCP) is obtained from NaPH2 (made from Na, P, and a proton source) and CO ...(from carbon and air). This salt is remarkably stable, in complete contrast to HCP discovered 50 years ago.
Lithium intercalation into the oxide slabs of the cation-deficient n = 2 Ruddlesden-Popper oxysulfide Y(2)Ti(2)O(5)S(2) to produce Li(x)Y(2)Ti(2)O(5)S(2) (0 < x < 2) is described. Neutron powder ...diffraction measurements reveal that at low levels of lithium intercalation into Y(2)Ti(2)O(5)S(2), the tetragonal symmetry of the host is retained: Li(0.30(5))Y(2)Ti(2)O(5)S(2), I4/mmm, a = 3.80002(2) A, c = 22.6396(2) A, Z = 2. The lithium ion occupies a site coordinated by four oxide ions in an approximately square planar geometry in the perovskite-like oxide slabs of the structure. At higher levels of lithium intercalation, the symmetry of the cell is lowered to orthorhombic: Li(0.99(5))Y(2)Ti(2)O(5)S(2), Immm, a = 3.82697(3) A, b = 3.91378(3) A, c = 22.2718(2) A, Z = 2, with ordering of Li(+) ions over two inequivalent sites. At still higher levels of lithium intercalation, tetragonal symmetry is regained: Li(1.52(5))Y(2)Ti(2)O(5)S(2), I4/mmm, a = 3.91443(4) A, c = 22.0669(3) A, Z = 2. A phase gap exists close to the transition from the tetragonal to orthorhombic structures (0.6 < x < 0.8). The changes in symmetry of the system with electron count may be considered analogous to a cooperative electronically driven Jahn-Teller type distortion. Magnetic susceptibility and resistivity measurements are consistent with metallic properties for x > 1, and the two-phase region is identified as coincident with an insulator to metal transition.
A novel approach was carried to prepare trans-CuCl2L2 complex with the ligand L, (E)-(4-chlorophenyl)-N-(3-phenyl-4H-1,2,4-triazol-4-yl)methanimine which was formed in situ during the reaction of ...CuCl2 with 4-(4-chlorobenzylideneamino)-5-phenyl-2H-1,2,4-triazole-3(4H)-thione. The synthesized compounds were characterized by applying various spectroscopic techniques. The crystal structure of the complex was unambiguously determined using X-ray analysis indicating square planar geometry. Intermolecular H-bonds govern the supramolecular structure of the copper complex. Aromatic rings are stacked in an offset packing due to occurrence of π–π interactions. The structure is further corroborated with a detailed computational investigation. A thione–thiol tautomerism for the triazole compound was also studied. The Schiff base 1,2,4-triazole copper chloride complex is expected to have high anticancer activity.
Two new strontium gallium nitrides were obtained as single crystals by reaction in molten Na. Black Sr3GaN3 is isostructural with its transition metal analogues, Sr3MnN3, Ba3MnN3, Sr3CrN3, Ba3CrN3, ...and Ba3FeN3, and is the first example of a 313-ternary nitride containing only main group metals. It crystallizes in space group P63/m (No. 176) with a = 7.584(2) Å, c = 5.410(3) Å, and Z = 2. Black Sr6GaN5 is isostructural with Ca6GaN5 and also with its transition metal analogues, Ca6MnN5 and Ca6FeN5. It crystallizes in space group P63/mcm (No. 193) with a = 6.6667(6) Å, c = 12.9999(17) Å, and Z = 2. Both Ga compounds contain isolated planar GaN36- nitridometallate anions of D 3 h symmetry.
