Robert Glaum

Chemical Vapor Transport Reactions

This comprehensive handbook covers the diverse aspects of chemical vapor transport reactions from basic research to important practical applications. The book begins with an overview of models for chemical vapor transport reactions and then proceeds to treat the specific chemical transport reactions for the elements, halides, oxides, sulfides, selenides, tellurides, pnictides, among others. Aspects of transport from intermetallic phases, the stability of gas particles, thermodynamic data, modeling software and laboratory techniques are also covered. Selected experiments using chemical vapor transport reactions round out the work, making this book a useful reference for researchers and instructors in solid state and inorganic chemistry.

New Results of Chemical Transport as a Method for the Preparation and Thermochemical Investigation of Solids.

Chemical transport experiments are a valuable aid of great potential in the synthesis and thermochemical characterization of solids. Compounds of interest can often only be crystallized by this method. The use of a transport balance allows very detailed observations, particularly of the course of the experiment over time (simultaneous or sequential deposition of multiple-phase solids). The computer program CVTRANS enables a quantitative thermochemical description of the experiment based on the cooperative transport model. A compilation of recent results illustrates the development and efficiency of the method. The transport of phosphides, anhydrous phosphates and sulfates, and rare-earth oxide and oxohalide compounds are treated in detail.

Intermediate states on the way to edge-sharing BO4 tetrahedra in M6B22O39·H2O (M=Fe, Co).

The new borates Fe(II)(6)B(22)O(39)·H(2)O (colourless) and Co(II)(6)B(22)O(39)·H(2)O (dichroic: red/bluish) were synthesised under the high-pressure/high-temperature conditions of 6 GPa and 880 °C (Fe)/950 °C (Co) in a Walker-type multi-anvil apparatus. The compounds crystallise in the orthorhombic space group Pmn2(1) (Z=2) with the lattice parameters a=771.9(2), b=823.4(2), c=1768.0(4) pm, V=1.1237(4) nm(3), R(1)=0.0476, wR(2)=0.0902 (all data) for Fe(6)B(22)O(39)·H(2)O and a=770.1(2), b=817.6(2), c=1746.9(4) pm, V=1.0999(4) nm(3), R(1)=0.0513, wR(2)=0.0939 (all data) for Co(6)B(22)O(39)·H(2)O. The new structure type of M(6)B(22)O(39)·H(2)O (M=Fe, Co) is built up from corner-sharing BO(4) tetrahedra and BO(3) groups, the latter being distorted and close to BO(4) tetrahedra if additional oxygen atoms of the neighbouring BO(4) tetrahedra are considered in the coordination sphere. This situation can be regarded as an intermediate state in the formation of edge-sharing tetrahedra. The structure consists of corrugated multiple layers interconnected by BO(3)/BO(4) groups to form Z-shaped channels. Inside these channels, iron and cobalt show octahedral (M1, M3, M4, M5) and strongly distorted tetrahedral (M2, M6) coordination by oxygen atoms. Co(II)(6)B(22)O(39)·H(2)O is dichroic and the low symmetry of the chromophore [Co(II)O(4)] is reflected by the polarised absorption spectra (Δ(t)=4650 cm(-1), B=878 cm(-1)).

The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate

Chromium(II) diphosphate, Cr(2)P(2)O(7), has an incommensurately modulated structure at ambient conditions with a = 7.05, b = 8.41, c = 4.63 A, beta = 108.71 degrees and q = (-0.361, 0, 0.471). It undergoes a phase transition towards a commensurate structure with a commensurate q vector, q = (-1/3, 0, 1/2), at T(c) = 285 K. The incommensurate structure has been solved by the charge-flipping method, which yielded both the basic positions of the atoms and the shapes of their modulation functions. The structure model for the commensurate structure was derived directly from the incommensurate structure. The structure analysis shows that the modulation leads to a change of the coordination of the Cr(2+) ions from distorted octahedra in the average structure towards a sixfold coordination in the form of a more regular octahedron and a fivefold coordination in the form of a square pyramid. The fivefold and sixfold coordination polyhedra alternate along the lattice direction a with the pattern 5-6-5 5-6-5 in the commensurate structure. In the incommensurate structure this pattern is occasionally disturbed by a 5-6-5-5 motif. Both structures can be described in superspace using the same superspace group and a similar modulated structure model. The same superspace model can also be used for the low-temperature phases of other metal diphosphates with the thortveitite stucture type at high temperature. Their low-temperature structures can be obtained from the superspace model by varying the q vector and the origin in the internal dimension t(0).

Preparation and Structure Determination of SrMn2(PO4)2 and Redetermination of b ′‐Mn3(PO4)2

Pale rose single crystals of SrMn2(PO4)2 were obtained from a mixture of SrCl2 · 6 H2O, Mn(CH3COO)2, and (NH4)2HPO4 after thermal decomposition and finally melting at 1100 °C. The new crystal structure of strontium manganese orthophosphate [P-1, Z = 4, a = 8.860(6) A, b = 9.054(6) A, c = 10.260(7) A, α = 124.27(5)°, β = 90.23(5)°, γ = 90.26(6)°, 4220 independent reflections, R1 = 0.034, wR2 = 0.046] might be described as hexagonal close-packing of phosphate groups. The octahedral, tetrahedral and trigonal-bipyramidal voids within this [PO4] packing provide different positions for 8- and 10-fold [SrOx] and distorted octahedral [MnO6] coordination according to a formulation MnMnMnSr(PO4)4. Single crystals of β′-Mn3(PO4)2 (pale rose) were grown by chemical vapour transport (850 °C → 800 °C, P/I mixtures as transport agent). The unit cell of β′-Mn3(PO4)2 [P21/c, Z = 12, a = 8.948(2) A, b = 10.050(2) A, c = 24.084(2) A, β = 120.50°, 2953 independent reflections, R1 = 0.0314, wR2 = 0.095] contains 9 independent Mn2+. The reinvestigation of the crystal structure led to distinctly better agreement factors and significantly reduced standard deviations for the interatomic distances.

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten XXXII [1] Neue Orthophosphate des zweiwertigen Chroms — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4†

Uber Festkorperreaktionen unter Beteiligung der Gasphase wurden in den Systemen A3(PO4)2 / Cr3(PO4)2 (A = Mg, Ca) die vier Verbindungen Mg3Cr3(PO4)4 (A), Mg3, 75Cr2, 25(PO4)4 (B), Ca3Cr3(PO4)4 (C) und Ca2, 00Cr4, 00(PO4)4 (D) erstmalig synthetisiert und mittels Einkristallstrukturanalyse charakterisiert [(A): P21/n, Z = 1, a = 4, 863(2) A, b = 9, 507(4) A, c = 6, 439(2) A, β = 91, 13(6)°, 1855 unabhangige Reflexe, 63 Variable, R1 = 0, 035, wR2 = 0, 083; (B): P21/a, Z = 2, a = 6, 427(2) A, b = 9, 363(2) A, c = 10, 051(3) A, β = 106, 16(3)°, 1687 unabh. Reflexe, 121 Variable, R1 = 0, 032, wR2 = 0, 085; (C): P-1, Z = 2, a = 8, 961(1) A, b = 8, 994(1) A, c = 9, 881(1) A, α = 104, 96(2)β, β = 106, 03(2)°, γ = 110, 19(2)°, 2908 unabh. Reflexe, 235 Variable, R1 = 0, 036, wR2 = 0, 111; (D): C2/c, Z = 4, a = 17, 511(2) A, b = 4, 9933(6) A, c = 16, 825(2) A, β = 117, 95(1)°, 1506 unabh. Reflexe, 121 Variable, R1 = 0, 034, wR2 = 0, 098]. Die Kristallstrukturen weisen mehrere kristallographisch unabhangige Lagen fur Chrom(II) auf, jeweils mit einer (4+n)-Koordination (n = 1, 2, 3). Bei den Magnesiumverbindungen und in Ca2, 00Cr4, 00(PO4)4 wird eine Fehlordnung der zweiwertigen Kationen Mg2+/Cr2+ bzw. Ca2+/Cr2+ beobachtet. Mg3, 75Cr2, 25(PO4)4 kristallisiert in einem neuen Strukturtyp, wahrend Mg3Cr3(PO4)4 isotyp zu Mg3(PO4)2 ist. Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4 sind im Aufbau nahe verwandt und gehoren zur Ca3Cu3(PO4)4-Strukturfamilie. Das Orthophosphat Ca9Cr(PO4)7 mit dreiwertigem Chrom wurde als Nachbarphase zu C und D erhalten. Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXII. New Orthophosphates of Divalent Chromium — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 and Ca2, 00Cr4, 00(PO4)4 Solid state reactions via the gas phase led in the systems A3(PO4)2 / Cr3(PO4)2 (A = Mg, Ca) to the four new compounds Mg3Cr3(PO4)4 (A), Mg3.75Cr2.25(PO4)4 (B), Ca3Cr3(PO4)4 (C), and Ca2.00Cr4.00(PO4)4 (D). These were characterized by single crystal structure investigations [(A): P21/n, Z = 1, a = 4.863(2) A, b = 9.507(4) A, c = 6.439(2) A, β = 91.13(6)°, 1855 independend reflections, 63 parameters, R1 = 0.035, wR2 = 0.083; (B): P21/a, Z = 2, a = 6.427(2) A, b = 9.363(2) A, c = 10.051(3) A, β = 106.16(3)°, 1687 indep. refl., 121 param., R1 = 0.032, wR2 = 0.085; (C): P-1, Z = 2, a = 8.961(1) A, b = 8.994(1) A, c = 9.881(1) A, α = 104.96(2)°, β = 106.03(2)°, γ = 110.19(2)°, 2908 indep. refl., 235 param., R1 = 0.036, wR2 = 0.111; (D): C2/c, Z = 4, a = 17.511(2) A, b = 4.9933(6) A, c = 16.825(2) A, β = 117.95(1)°, 1506 indep. refl., 121 param., R1 = 0.034, wR2 = 0.098]. The crystal structures contain divalent chromium on various crystallographic sites, each showing a (4+n)-coordination (n = 1, 2, 3). For the magnesium compounds and Ca2.00Cr4.00(PO4)4 a disorder of the divalent cations Mg2+/Cr2+ or Ca2+/Cr2+ is observed. Mg3.75Cr2.25(PO4)4 adopts a new structure type, while Mg3Cr3(PO4)4 is isotypic to Mg3(PO4)2. Ca3Cr3(PO4)4 and Ca2.00Cr4.00(PO4) 4 are structurally very closely related and belong to the Ca3Cu3(PO4)4-structure family. The orthophosphate Ca9Cr(PO4)7, containing trivalent chromium, has been obtained besides C and D.

Neues zum chemischen Transport als Methode zur Präparation und thermochemischen Untersuchung von Festkörpern

Chemische Transportexperimente stellen ein wertvolles, weithin noch nicht ausgeschopftes Hilfsmittel bei der Synthese und thermochemischen Charakterisierung von Feststoffen dar. Oftmals lassen sich die interessierenden Verbindungen nur auf diesem Wege kristallisieren. Die Verwendung einer Transportwaage gestattet sehr detaillierte Beobachtungen, insbesondere zum zeitlichen Verlauf (simultane oder sequentielle Abscheidung mehrphasiger Bodenkorper) eines Experimentes. Mit dem Computerprogramm CVTRANS ist im Rahmen des Modells des kooperativen Transports die quantitative thermochemische Beschreibung der Experimente moglich. Eine Zusammenstellung neuerer Ergebnisse veranschaulicht die Entwicklung und Leistungsfahigkeit der Methode. Behandelt wird besonders der Transport von Phosphiden, wasserfreien Phosphaten und Sulfaten sowie von Oxo- und Oxohalogenoverbindungen der Seltenen Erden.

Towards Physical Descriptors of Active and Selective Catalysts for the Oxidation of n‐Butane to Maleic Anhydride

Based on our newly developed microwave cavity perturbation technique, the microwave conductivity of diverse vanadium(III), (IV), and (V) phosphate catalysts was measured under reaction conditions for the selective oxidation of n‐butane. The conductivity response on the gas phase was identified as a very sensitive measure for the redox kinetics, reversibility, and stability of the samples, which are important prerequisites for highly selective and active catalysts. The sensitivity achieved by our method was comparable to surface‐sensitive methods such as X‐ray photoelectron spectroscopy, whereas more conventional analytic techniques such as X‐ray diffractometry or Raman spectroscopy only indicated the stability of the bulk crystal phase under the same reaction conditions.

Homonuclear Mixed‐Valent Cobalt Imidazolate Framework for Oxygen‐Evolution Electrocatalysis

Herein, the synthesis and characterization of the first mixed-valent, purely cobalt-based zeolitic imidazolate framework, Co(II)3Co(III)2(C3H3N2)12 is presented. The material adopts the cubic garnet-type structure and combines high thermal stability of up to 350 °C with excellent chemical stability. Electrochemical characterization showed that the cobalt centres are redox active and efficiently support oxygen evolution, thus rendering this framework a potential candidate for single-site heterogeneous catalysis based on earth-abundant elements.

Beiträge zum thermischen Verhalten wasserfreier Phosphate

We describe the synthesis and crystallisation by means of chemical vapour transport reactions of TiP04 and VP04. TiP04 (a = 5.2985(5) A, b = 7.911(1) Ä, c = 6.3473(5) A) and VP04 (a = 5.2316(5) A, b = 7.7738(7) A, c = 6.2847(5) A) adopt the crystal structure of chromiumvanadate CrV04 (Cmcm, Ζ = 4). The results of the refinements of both crystal structures from single crystal data are given. TiP04 (VP04): 335 (223) symmetry independent reflections from 1260 (1439) reflections, 22 (22) variables, residuals. R = 0.062 (0.049).