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[13] viXra:2610.0064 [pdf] submitted on 2026-10-15 06:05:24
Authors: Roberto Köferstein, Michael Arnold, Christian Robl
Comments: 12 Pages. The paper was published in: Z. Anorg. Allg. Chem. 643 (2017) 276—285. (Highlighted as cover picture 03/2017, DOI: 10.1002/zaac.201600457)
Blue single crystals of Cu[µ2-OOC(CH2)PO3H]*2H2O (1) and Cu1.5[µ3-OOC(CH2)PO3]*5H2O (2) have been prepared in aqueous solution. 1: Space group C2/c (no. 15) with a = 1623.3(2), b = 624.0(1), c = 1495.5(2) pm, beta = 122.45(1)°. Cu is coordinated by three oxygen atoms stemming from the hydrogenphosphonoacetate dianion and three water molecules to form a distorted octahedron. The Cu-O bonds range from 190.4(3) to 278.5(3) pm. The connection between the Cu2+ cations and the hydrogenphosphonoacetate dianions leads to a two-dimensional structure with layers parallel to (-101). ̅The layers are linked by hydrogen bonds. 2: Space group P-1 (no. 2) with a = 608.2(1), b = 800.1(1), c = 1083.6(1) pm,alpha = 94.98(1)°, beta = 105.71(1)°, gamma = 109.84(1)°. There are two crystallographically independent Cu2+ cations coordinated in a square pyramidal and an octahedral fashion, respectively. The Cu-O bonds range from 192.9(2) to 237.2(2) pm. The coordination of the phosphonoacetate trianion to Cu(1) results in infinite polyanionic chains parallel to [100] with a composition of {Cu(H2O)[OOC(CH2)PO3]}nn-. Hydrated Cu(2) cations are accommodated between the chains as counter ions. 1 and 2 show structural features of cation exchangers. Magnetic measurements reveal a paramagnetic Curie-Weiss behaviour. Compound 2 shows antiferromagnetic coupling between Cu2+ ions due to a super-superexchange coupling. The UV/Vis spectra of 1 suggests three d-d transition bands at 763 nm (2B1 -> 2E), 878 nm (2B1 -> 2B2), and 1061 nm (2B1 -> 2A1). Thermoanalytical investigations in air show that compound 1 is stable up to 165 °C, whereas the decomposition of 2 begins at 63 °C.
Category: Chemistry
[12] viXra:2610.0060 [pdf] submitted on 2026-10-13 08:32:29
Authors: Roberto Köferstein, Michael Arnold, Christian Robl
Comments: 9 Pages. The paper was published in: Z. Anorg. Allg. Chem. 642 (2016) 1126—1132. (DOI: 10.1002/zaac.201600248)
Turquoise monoclinic single crystals of the novel three-dimensional Cu2[µ8-O3P(CH2)2PO3)]*3.2H2O coordination polymer have been prepared using the silica gel method. Space group C2/m (no. 12) with a = 1483.6(2), b = 668.44(8), c = 436.30(6) pm, beta = 93.28(2)°. The Cu2+ cation is coordinated by four oxygen atoms stemming from the 1,2-ethylenediphosphonate dianions in a square planar manner and two water molecules in the axial positions. The connection between the Cu2+ cations and the [PO3C] units from the 1,2-ethylenediphosphonate dianions leads to layers parallel to (100), which are linked by the ethylene groups to a three-dimensional framework with channel-like voids. The voidsaccommodate water molecules not bound to Cu2+ and extend parallel along [001] with an opening of about 550 x 260 pm. Magnetic measurements reveal an antiferromagnetic behaviour due to a superexchange coupling between Cu2+ ions through an oxygen bridge. The UV-Vis spectrum reveals three d-d transition bands at 694, 774, and 918 nm. The compound can be fully dehydrated by thermal treatment and rehydrated by storage in ambient air.
Category: Chemistry
[11] viXra:2610.0058 [pdf] submitted on 2026-10-13 08:56:36
Authors: Roberto Köferstein, Michael Arnold, Christian Robl
Comments: 16 Pages. The paper was published in: Z. Anorg. Allg. Chem. 644 (2018) 205—214. (Highlighted as cover picture 04/2017, DOI: 10.1002/zaac.201700453)
Blue single crystals of Cu[µ3-O3P(CH2)2COOH]*2H2O (1) and Cu[(RS)-µ3-O3PCH(C2H5)COOH]*3H2O (2) have been prepared in aqueous Cu2+-solutions (pH = 2.5—3.5) containing 3-phosphonopropionic acid (1) and (RS)-2-phosphonobutyric acid (2), respectively. 1: Space group Pbca (no. 61) with a = 812.5(2), b = 919.00(9), c = 2102.3(2) pm. Cu2+ is five-fold coordinated by three oxygen atoms stemming from [O3P(CH2)2COOH]2— anions and two water molecules. The Cu-O bond lengths range from 194.0(3) to 231.8(4) pm. The connection between the [O3P(CH2)2COOH]2— anions and the Cu2+ cations yields a polymeric structure with layers parallel to (001). The layers are linked by hydrogen bonds. 2: Space group Pbca (no. 61) with a = 1007.17(14), b = 961.2(3), c = 2180.9(4) pm. The copper cations are surrounded by five oxygen atoms in a square pyramidal fashion with Cu-O bonds between 193.6(4) and 236.9(4) pm. The coordination between [O3PCH(C2H5)COOH]2- and Cu2+ results in infinite puckered layers parallel to (001). The layers are not connected by any hydrogen bonds. Each layer contains both R and S isomers of the [O3PCH(C2H5)COOH]2- dianion. Water molecules not bound to Cu2+ are intercalated between the layers. UV/Vis spectra suggest three d-d transition bands at 743, 892, 1016 nm for 1 and four bands at 741, 838, 957 and 1151 nm for 2, respectively. Magnetic measurements suggest a weak antiferromagnetic coupling between Cu2+ due to a super-superexchange interaction. Thermoanalytical investigations in air show that the compounds are stable up to 95 °C (1) and 65 °C (2), respectively.
Category: Chemistry
[10] viXra:2610.0054 [pdf] submitted on 2026-10-12 11:04:13
Authors: Roberto Köferstein, Christian Robl
Comments: 9 Pages. The paper was published in: Z. Anorg. Allg. Chem. 640 (2014) 310—316 (DOI: 10.1002/zaac.201300527)
Two new three-dimensional frameworks with zeolite-like channels have been prepared in the presence of 1,6-diaminohexane. Cu1.5(H3N-(CH2)6-NH3)0.5[C6H2(COO)4]*5H2O (1) crystallizes in the triclinic space group P-1with a = 772.56(7), b = 1110.36(7), c = 1111.98(8) pm, alpha = 98.720(7)°, beta = 108.246(9)° and gamma = 95.559(7)°. Cu2(H3N-(CH2)6-NH3)0.5(OH)[C6H2(COO)4]*3H2O (2) crystallizes in the monoclinic space group P2/c with a = 1159.34(11), b = 1059.44(7), c = 1582.2(2) pm and = 106.130(11)°. The Cu2+ coordination polyhedra are connected by [C6H2(COO)4]4- anions to yield three-dimensional frameworks with wide centrosymmetric channel-like voids. Complex 1 reveals voids extending along [100] with diagonals of 900 pm and 300 pm, whereas in complex 2 the diagonal of the nearly rectangular crossection of the channels extending parallel to [001] is 900 pm. The negative excess charges of the frameworks are compensated by [H3N-(CH2)6-NH3]2+-cations, which occupy the voids along with water molecules. The [H3N-(CH2)6-NH3]2+-cations are not connected to Cu2+ and have served as templates.
Category: Chemistry
[9] viXra:2610.0053 [pdf] submitted on 2026-10-12 11:02:14
Authors: Roberto Köferstein, Christian Robl
Comments: 9 Pages. The paper was published in: Z. Anorg. Allg. Chem. 641 (2015) 1886-1891. (DOI: 10.1002/zaac.201500231)
Abstract. Blue monoclinic single crystals of the novel one-dimensional [H3N-(CH2)6-NH3][Cu(H2O)2(urea)(µ2-C6(COO)4 (COOH)2)]*H2O coordination polymer have been prepared in aqueous solution at room temperature in the presence of 1,6-diaminohexane and urea. Space group P21/n (no. 14) with a = 958.48(9), b = 1465.74(11), c = 1821.14(12) pm, beta = 97.655(8)°. The Cu2+ cation is coordinated in a square pyramidal manner by two oxygen atoms stemming from the dihydrogen mellitate tetraanion, one oxygen atom from the urea molecule, and two water molecules. The Cu−O distances are between 193.3(2) and 229.4(2) pm. The connection between Cu2+ and [C6(COO)4(COOH)2]4- yields infinite chain-like polyanions parallel to [-101] with a composition of {Cu(H2O)2(urea)[C6(COO)4(COOH)2]}n2n-. The dihydrogen mellitate tetraanion adopts a µ2 coordination mode. The [(H3N-(CH2)6-NH3)]2+ cations are accommodated between the chains as counter cations. The hexane-1,6-diammonium cations adopt a partial synclinal conformation. The chains are connected by strong and weak hydrogen bonds. Magnetic measurements reveal a paramagnetic Curie-Weiss behaviour and a magnetic moment of 1.93 µB per Cu2+. Thermoanalytical investigations in air show that the complex is stable up to 135 °C. Following decomposition processes yielding CuO.
Category: Chemistry
[8] viXra:2610.0052 [pdf] submitted on 2026-10-12 11:01:47
Authors: Roberto Köferstein, Christian Robl
Comments: 10 Pages. The paper was published in: Z. Anorg. Allg. Chem. 642 (2016) 560—565. (DOI: 10.1002/zaac.201600080)
Black-brown needle-shaped single crystals of [Co2(en)4(O2)(OH)][C4O4]1.5*H2O (en = ethylenediamine) have been prepared in aqueous solution at room temperature. Space group P1 ̅ (no.2) with a = 800.20(8), b = 1225.48(7), c = 1403.84(9) pm, alpha = 100.282(5), beta = 94.515(7), gamma = 95.596(6)°. The Co3+ cations [Co(1), Co(2)] are coordinated in an octahedral manner by four nitrogen atoms stemming from the ethylenediamine molecules and two oxygen atoms each from a hydroxo group and a peroxo group, respectively. Both Co3+ coordination polyhedra are connected by a common corner and by the peroxo group leading to the binuclear [(en)2Co(O2)(OH)Co(en)2]3+ cation. The squarate dianions, not bonded to Co3+, and the [(en)2Co(O2)(OH)Co(en)2]3+ cations are linked by hydrogen bonds forming a three-dimensional supramolecular network containing water molecules. Magnetic measurements reveal a diamagnetic behaviour indicating a low-spin electron configuration of Co3+. The UV-Vis spectra shows two LMCT bands (pi*(O22-) -> d(sigma)*(Co3+)) at 274 and 368 nm and the d-d transition (1A1g -> 1T1g) at 542 nm. Thermoanalytical investigations in air show that the compound is stable up to 120 °C. Subsequent decomposition processes to cobalt oxide are finished at 460 °C.
Category: Chemistry
[7] viXra:2610.0051 [pdf] submitted on 2026-10-12 11:01:20
Authors: Roberto Köferstein, Christian Robl
Comments: 8 Pages. The paper was published in: Z. Anorg. Allg. Chem. 641 (2015) 1150—1155. (DOI: 10.1002/zaac.201500050)
Monoclinic single crystals of Ba2(H2O)[µ10-C6H2(COO)4] (1) and Pb2(H2O)[µ10-C6H2(COO)4]*H2O (2) have been obtained using the silica gel method. Space group C2/c (no. 15), Z = 4; 1: a = 780.89(4), b = 1756.19(8), c = 914.80(5) pm, beta= 114.512(5)°; 2: a = 756.70(10), b = 1772.8(2), c = 890.2(2) pm, beta= 113.590(10)°. There are two crystallographically independent M2+ ions (M = Ba, Pb). M(1) is surrounded by eight carboxylate oxygen atoms and one water molecule forming a tricapped trigonal prism. M(2) is coordinated by ten carboxylate oxygen atoms in the shape of a tetracapped octahedron. The connection between the M(1) and M(2) polyhedra leads to infinite layers parallel to (010) which are linked by [C6H2(COO)4]4- anions to form a three-dimensional framework. The [C6H2(COO)4]4- anion adopts a µ10 coordination mode. Compound 1 reveals short Ba-Ba contacts of 426.46(2) pm, whereas the Pb-Pb distance of 411.01(6) pm in 2 is larger than twice the van der Waals radius.
Category: Chemistry
[6] viXra:2610.0049 [pdf] submitted on 2026-10-12 12:46:14
Authors: Sven Harms, Roberto Köferstein, Helmar Görls, Christian Robl
Comments: 13 Pages. The paper was published in: Z. Anorg. Allg. Chem. 645 (2019) 912—918. (DOI: 10.1002/zaac.201900089)
Colourless single crystals of Cd2[µ8-MTB]*3H2O*DMF (1) were prepared in DMF/H2O solution. 1: Space group C2/c (no. 15) with a = 1821.30(6), b = 2175.08(6), c = 1269.87(4) pm, beta = 129.684(1)°. The connection between the methane-p-benzoate tetraanions (MTB4-) and the Cd2+ cations leads to a three-dimensional framework with channels extending along [1-10] and [110] with openings of 670 pm x 360 pm. The channel-like voids accommodate water molecules and N,N-dimethylformamide (DMF) molecules not bound to Cd2+. Colourless single crystals of [Cd4(2,2'-bipy)4(µ7-MTB)2]*7DMF (2) were prepared in DMF in the presence of 2,2'-bipyridine. 2: Space group P-1 (no. 2) with a = 1224.84(4), b = 1418.85(5), c = 2033.49(4) pm, alpha = 85.831(2)°, beta = 88.351(2)°, gamma = 68.261(1)°. The coordination of MTB4- to Cd2+ results in infinite layers parallel to (001). The layers, not connected by any hydrogen bonds, contain small openings of about 320 pm x 340 pm.
Category: Chemistry
[5] viXra:2610.0035 [pdf] submitted on 2026-10-10 00:37:37
Authors: Roberto Köferstein, Christian Robl
Comments: 8 Pages. The papaer was published in: Z. Anorg. Allg. Chem. 640 (2014) 1937—1942. (DOI: 10.1002/zaac.201400177)
Abstract. Triclinic single crystals of Cu4(H3N-(CH2)9-NH3)(OH)2[C6H2(COO)4]2*5H2O have been prepared in aqueous solution at 80 °C in the presence of 1,9-diaminononane. Space group P-1 (no. 2) with a = 1057.5(2), b = 1166.0(2), c = 1576.7(2) pm, alpha = 106.080(10)°, beta = 90.73(2)° and gamma = 94.050(10)°. The four crystallographic independent Cu2+ ions are surrounded by five oxygen atoms each with Cu−O distances between 191.4(3) and 231.7(4) pm. The connection between the Cu2+ coordination polyhedra and the [C6H2(COO)4]4- anions leads to a three-dimensional framework with negative excess charge and wide centrosymmetric channel-like voids.These voids extend parallel to [001] with the diagonal of the nearly rectangular crossection of approximately 900 pm. The channels of the framework accommodate [H3N-(CH2)9-NH3]2+-cations and water molecules, which are not connected to Cu2+. The nonane-1,9-diammonium-cations adopt a partial gauche conformation. Thermoanalytical measurements in air show a loss of water of crystallization starting at 90 °C and finishing at approx. 170 °C. The dehydrated compound is stable up to 260 °C followed by an exothermic decomposition yielding copper oxide.
Category: Chemistry
[4] viXra:2610.0031 [pdf] submitted on 2026-10-09 00:06:20
Authors: Roberto Köferstein, Stefan G. Ebbinghaus
Comments: 42 Pages. The paper was published in: J. Eur. Ceram. Soc. 43 (2023) 6137—6144. (Open Access, DOI: 10.1016/j.jeurceramsoc.2023.06.040)
Magnetoelectric (NiFe2O4)0.3-(Sr0.5Ba0.5Nb2O6)0.7 composites with addition of LiNbO3 as sintering additive were prepared by a classical mixed-oxide method. XRD patterns of ceramics sintered between 1000 and 1200 °C show the desired Sr0.5Ba0.5Nb2O6 and NiFe2O4 phases. SEM investigations confirm the 0-3 connectivity of the composite ceramics. The addition of 10 and 20 mol% LiNbO3 improves the densification of the composite ceramics and leads to an increase of the size of the Sr0.5Ba0.5Nb2O6 grains. Magnetic measurements show hystereses with low coercivities. Dielectric measurements were carried out depending on temperature and frequency. The samples with the LiNbO3 addition show significantly higher resistivity values (sDC). Magnetoelectric measurements were carried out in dependence of the magnetic DC-field, temperature, and frequency. The maximum magnetoelectric coefficient (aME) rises with the addition of LiNbO3 from 180 to 803 µV Oe-1 cm-1 (@ 900 Hz). Temperature dependent measurements show a continuously decreasing of aME with lower temperature.
Category: Chemistry
[3] viXra:2610.0030 [pdf] submitted on 2026-10-09 00:06:02
Authors: Roberto Köferstein, Florian Oehler, Stefan G. Ebbinghaus
Comments: 40 Pages. The paper was published in: Mater. Chem. Phys. 278 (2022) 125616. (Open Access, DOI: 10.1016/j.matchemphys.2021.125616)
Magnetoelectric (Sr0.5Ba0.5Nb2O6)1-x-(CoFe2O4)x (x = 0.2-0.6) composites were prepared by a one-pot soft-chemistry synthesis using PEG400. Calcining at 700 °C resulted in nanocrystalline composite powders (dcryst. = 24-30 nm) which were sintered between 1050 and 1200 °C to ceramic bodies with relative densities up to 98 %. SEM investigations confirm the formation of composite ceramics with a 0-3 connectivity and variable grain sizes from 0.2 to 3.6 µm for sintering up to 1150 °C, while sintering at 1200 °C leads both to a change in the microstructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviour with saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe. Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both with rising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described using a single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. The maximum magnetoelectric coefficient (aME) depends both on the CoFe2O4 fraction (x) and sintering temperature. The composite with x = 0.3 exhibits the largest aME value of 37 µV Oe-1 cm-1 (@ 900 Hz). With rising frequency of the AC driving field aME increases up to 300-400 Hz and is nearly constant until 1 kHz.
Category: Chemistry
[2] viXra:2610.0029 [pdf] submitted on 2026-10-09 00:05:47
Authors: Roberto Köferstein, Stefan G. Ebbinghaus
Comments: 42 Pages. The paper was published in: , J. Solid State Chem. 278 (2022) 123564. (Open Access, DOI: 10.1016/j.jssc.2022.123564)
Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives were prepared by a soft-chemistry synthesis using polyethylene glycol. Calcination at 600 °C results in nanocrystalline powders (dcryst. ~ 30 nm) which were sintered between 1000 and 1300 °C to ceramic bodies. By addition of 10 and 20 mol% LiNbO3, the sintering temperature was reduced by about 200 K and the activation energy of the initial stage of sintering decreases from 386 to 271 kJ mol-1. The sintering aid improves the grain growth and dense ceramic bodies were obtained after sintering at 1125 °C for 1 h. A higher LiNbO3 content favors the formation of a pillar-like microstructure. XRD patterns of ceramics sintered above 1000 °C show only reflections of the Sr0.5Ba0.5Nb2O6 phase indicating an incorporation of LiNbO3 in the Sr0.5Ba0.5Nb2O6 structure. Dielectric measurements reveal a diffuse phase transition and a relaxor-like behavior. The phase transition temperature (Tm) depends on the sintering conditions and is between 117 and 127 °C for 10 mol% LiNbO3, which is very close to pure Sr0.5Ba0.5Nb2O6, while addition of 20 mol% shifts Tm to around 200 °C and the transition becomes slightly more diffuse. The optical band gap of the samples is ~ 3.3 eV and depends slightly on the sintering conditions. We also tried LiF as sintering aid, but this leads to the formation of considerable amounts of secondary phases in the ceramics and relative densities of only 82 %.
Category: Chemistry
[1] viXra:2610.0023 [pdf] submitted on 2026-10-06 20:18:35
Authors: R. Köferstein, J. Jacobs, S. G. Ebbinghaus
Comments: 40 Pages. The paper was published in: J. Eur. Ceram. Soc. 45 (2025) 117567. (Open Access, DOI: 10.1016/j.jeurceramsoc.2025.117567).
Lix(Sr0.5Ba0.5)1-x/2Nb2O6 ceramics were prepared by a solid state synthesis and sintered at 1300 °C. XRD investigations reveal single phase samples up to a substitution limit of x = 0.275. For higher lithium contents, the appearance of LiNbO3 as secondary phase was observed. The density of the ceramics increases with lithium content. The microstructures show globular grains which turns to pillar-like grains with rising lithium substitution. Dielectric investigations confirm relaxor ferroelectric behavior and the diffuse phase transition is shifted towards higher temperatures with increasing lithium content from 129 °C (x = 0) to 221 °C (x = 0.275). The diffuseness coefficient increases with the lithium content. From high-temperature XRD measurements the length of the tetragonal cell parameter c decreases with increasing temperature, reaches a minimum at about 150-230 °C (depending on x) and afterward increases with increasing temperature. Additionally, a significant shift of the Nb(2) position with temperature can be observed.
Category: Chemistry
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