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The optoelectronic properties of two layered copper oxyselenide compounds, with nominal composition Sr 2 ZnO 2 Cu 2 Se 2 and Ba 2 ZnO 2 Cu 2 Se 2 , have been investigated to determine their suitability as p-type conductors. The structure, band gaps and electrical conductivity of pristine and alkali-metal-doped samples have been determined. We find that the strontium-containing compound, Sr 2 ZnO 2 Cu 2 Se 2 , adopts the expected tetragonal Sr 2 Mn 3 SbO 2 structure with I 4/ mmm symmetry, and has a band gap of 2.16 eV, and a room temperature conductivity of 4.8 × 10 -1 S cm -1 . The conductivity of the compound could be increased to 4.2 S cm -1 when sodium doped to a nominal composition of Na 0.1 Sr 1.9 ZnO 2 Cu 2 Se 2 . In contrast, the barium containing material was found to have a small zinc oxide deficiency, with a sample dependent compositional range of Ba 2 Zn 1- x O 2- x Cu 2 Se 2 where 0.01 < x < 0.06, as determined by single crystal X-ray diffraction and powder neutron diffraction. The barium-containing structure could also be modelled using the tetragonal I 4/ mmm structure, but significant elongation of the oxygen displacement ellipsoid along the Zn-O bonds in the average structure was observed. This indicated that the oxide ion position was better modelled as a disordered split site with a displacement to change the local zinc coordination from square planar to linear. Electron diffraction data confirmed that the oxide site in Ba 2 Zn 1- x O 2- x Cu 2 Se 2 does not adopt a long range ordered arrangement, but also that the idealised I 4/ mmm structure with an unsplit oxide site was not consistent with the extra reflections observed in the electron diffractograms. The band gap and conductivity of Ba 2 Zn 1- x O 2- x Cu 2 Se 2 were determined to be 2.22 eV and 2.0 × 10 -3 S cm -1 respectively. The conductivity could be increased to 1.5 × 10 -1 S cm -1 with potassium doping in K 0.1 Ba 1.9 Zn 1- x O 2- x Cu 2 Se 2 . Hall measurements confirmed that both materials were p-type conductors with holes as the dominant charge carriers., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The synthesis and structure of two new transition metal oxide tellurides, Sr 2 MnO 2 Cu 1.82(2) Te 2 and Sr 2 CoO 2 Cu 2 Te 2 , are reported. Sr 2 CoO 2 Cu 2 Te 2 with the purely divalent Co 2+ ion in the oxide layers has magnetic ordering based on antiferromagnetic interactions between nearest neighbors and appears to be inert to attempted topotactic oxidation by partial removal of the Cu ions. In contrast, the Mn analogue with the more oxidizable transition metal ion has a 9(1)% Cu deficiency in the telluride layer when synthesized at high temperatures, corresponding to a Mn oxidation state of +2.18(2), and neutron powder diffraction revealed the presence of a sole highly asymmetric Warren-type magnetic peak, characteristic of magnetic ordering that is highly two-dimensional and not fully developed over a long range. Topotactic oxidation by the chemical deintercalation of further copper using a solution of I 2 in acetonitrile offers control over the Mn oxidation state and, hence, the magnetic ordering: oxidation yielded Sr 2 MnO 2 Cu 1.58(2) Te 2 (Mn oxidation state of +2.42(2)) in which ferromagnetic interactions between Mn ions result from Mn 2+/3+ mixed valence, resulting in a long-range-ordered A-type antiferromagnet with ferromagnetic MnO 2 layers coupled antiferromagnetically.

The structures of two new oxide chalcogenide phases, Sr 2 CuO 2 Cu 2 S 2 and Sr 2 CuO 2 Cu 2 Se 2 , are reported, both of which contain infinite CuO 2 planes containing Cu 2+ and which have Cu + ions in the sulfide or selenide layers. Powder neutron diffraction measurements show that Sr 2 CuO 2 Cu 2 Se 2 exhibits long-range magnetic ordering with a magnetic structure based on antiferromagnetic interactions between nearest-neighbor Cu 2+ ions, leading to a √2 a × √2 a × 2 c expansion of the nuclear cell. The ordered moment of 0.39(6) μ B on the Cu 2+ ions at 1.7 K is consistent with the value predicted by density functional theory calculations. The compounds are structurally related to the cuprate superconductors and may also be considered as analogues of the parent phases of this class of superconductor such as Sr 2 CuO 2 Cl 2 or La 2 CuO 4 . In the present case, however, the top of the chalcogenide-based valence band is very close to the vacant Cu 2+ 3d states of the conduction band, leading to relatively high measured conductivity.

For the collidine analogues of Barluenga's Reagent (IPy 2 BF 4 ) reported, a flat cation is necessary for the generation of a modulated phase, in keeping with the "Ratchet Model" theory [Kim et al., Crystal Growth & Design, 2014, 14, 6294]. Attempts to study "diffuse modulation" in Br(Coll) 2 ClO 4 have shown that these non-Bragg features disappear very rapidly on exposure to synchrotron radiation, an effect thought to be caused by the radiation damage disrupting the lattice vibrations that cause the modulation.

Lithiation of hydrothermally synthesized Li 1-x Fe x (OH)Fe 1-y Se turns on high-temperature superconductivity when iron ions are displaced from the hydroxide layers by reductive lithiation to fill the vacancies in the iron selenide layers. Further lithiation results in reductive iron extrusion from the hydroxide layers, which turns off superconductivity again as the stoichiometric composition Li(OH)FeSe is approached. The results demonstrate the twin requirements of stoichiometric FeSe layers and reduction of Fe below the +2 oxidation state as found in several iron selenide superconductors.

CaCoSO, synthesized from CaO, Co, and S at 900 °C, is isostructural with CaZnSO and CaFeSO. The structure is non-centrosymmetric by virtue of the arrangement of the vertex-sharing CoS3O tetrahedra which are linked by their sulfide vertices to form layers. The crystal structure adopts space group P63mc (No. 186), and the lattice parameters are a = 3.7524(9) Å and c = 11.138(3) Å at room temperature with two formula units in the unit cell. The compound is highly insulating, and powder neutron diffraction measurements reveal long-range antiferromagnetic order with a propagation vector k = (1/3, 1/3, 1/2). The magnetic scattering from a powder sample can be modeled starting from a 120° arrangement of Co(2+) spin vectors in the triangular planes and then applying a canting out of the planes which can be modeled in the magnetic space group C(c)c (space group 9.40 in the Belov, Neronova, and Smirnova (BNS) scheme) with Co(2+) moments of 2.72(5) μ(B). The antiferromagnetic structure of the recently reported compound BaCoSO, which has a very different crystal structure from CaCoSO, is also described, and this magnetic structure and the magnitude of the ordered moment (2.75(2) μ(B)) are found by experiment to be similar to those predicted computationally.