In contrast to well established experimental results of vibronic coupling effects in octahedral dn complexes with Eg ground states (Cu2+, Ag2+; Cr2+, Mn3+ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dn cations – in particular for TiIII, VIII and high-spin CoIII, NiIII with T2g and T1g ground states, which involve, to first-order, solely splitting of the π-antibonding t2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the Tg⊗(ɛg+τ2g) vibronic interaction as well as in the Eg⊗ɛg coupling case (MnIII, low-spin NiIII); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dn ligand field matrices in Oh, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (CrIII, 4A2g ground state). The group-theoretical analysis of the interaction with the JT-active ɛg and τ2g modes yields D4h, D3d and D2h as the possible distortion symmetries in the case of a Tg ground state. The DFT-calculations give clear evidence, that the D4h stationary points represent the absolute minima in the Tg⊗(ɛg+τ2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited Tg states, can be presented for trivalent 3dn cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding eg MOs.

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The results of single crystal X-ray structure determinations are reported for Ba2CaCuV2F14 (a = 1383.6(3), b = 540.89(8), c = 1493.1(3) pm, beta = 91.65(3)degrees) and Ba2CaCuCr2F14 (a = 1381.1(5), b = 535.5(1), c = 1481.4(.6) pm, beta = 91,50(4)degrees), both iscitypic with usovite (space group C2/c, Z = 4). The resulting average distances are V-F: 193.8 pm, Cr-F: 190.7 pm, and Cu-F: 209.2 resp. 207.1 pm flor the Jahn-Teller elongated [CuF6] octahedra. Within the cross-linked double chains of octahedra F-bridged trimers M-Cu-M, magnetically studied earlier, are confirmed and discussed.

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Orthorhombic CsFe2F6 (a = 749.1(3), b = 723.8(3), c = 1043.1(6) pm; V = 565.6(9) angstrom(3), Z = 4, Imma ?) was prepared with strongly Fe-57 doped FeF3 and its Mossbauer spectra measured. It is in accordance with the spectra of a natural 57 Fe abundance sample, also with respect to the intensity ratio (FeFeIII)-Fe-II = 1:1. For the formation of an ordered pyrochlore structure in spite of quenching thus an electronically induced phase transition should be responsible, explaining the M-II/M-III order observed in all mixed valence pyrochlores A(I)M(II)M(III)F(6). By contrast, single crystals of CsMgGaF6 (a = 1021.6(1)pm), CsMnVF6 (a = 1058.9(1) pm), CsMnFeF6 (a = 1054.6(1) pm), CsZnVF6 (a = 1041.5(1) pm, CsZnFeF6 (a = 1042.1 (1) pm) and CsCuFeF6 (a = 1037.7(2) pm), obtained by solid state reaction and slow cooling, all exhibit the cubic pyrochlore structure of the RbNiCrF6 type (Z = 8, Fd (3) over barm), in which the cations M-II/M-III are disordered in position (16c). An oxidfluoride of approximate composition Cs4Cu5V3O2F19 (a = 1022.2(1) pm) has the same structure, but in addition it shows a disordered occupation of the position (48f) by lack of about 1/8 of anions. Structural relations and distances for the cubic crystal structures refined (R between 0.02 and 0.06) are discussed.

Preparing BaMnAlF7 we obtained single crystals of Ba3Al2F12 as a by-product (a = 1020.3(2), b = 988.5(1), c = 952.2(1) pm, space group Pnnm, Z = 4). The redetermination confirmed the structure already known, but improved the results (R-1' = 0.028 and wR(2) = 0.06 for 1908 and 2717 reflections, resp.). An interpretation is given for the relation of distances within the tetrameric anion [Al4F20](8-) (average Al-F: 180,1 pm). The construction of the cationic frame [Ba3F2](4+) is discussed.

The crystal structure of KCuGaF6 was determined on the base of X-ray single crystal data (wR(2) = 0.084 for 2476 independent reflections). The compound crystallizes with a = 728.56(4), b = 989.51(6), c = 676.27(3) pm, beta = 93.120(5)degrees, Z = 4 in space group P2(1)/c of the pyrochlore related KCuCrF6 type. The octahedral coordinations [GaF6] and [CuF6] are slightly resp. strongly distorted (mean values Ga-F: 188.2 pm resp. Cu-F: 188.2/200. 1/ 227.6 pm). The longest distances Ga-F and the shortest ones Cu-F are found within octahedral chains of these two kinds of atoms, running along [100] and [001], resp., and being mutually bridged as well (M-F-M in between 114 and 145degrees). The magnetic mole susceptibilities measured at powders and at a single crystal follow the isotropic Heisenberg model for S = 1/2, if effects of chain disrupture are considered in the form of some paramagnetic portion. No indication of threedimensional magnetic order is observed down to T = 2 K and low magnetic fields H < 100 G. KCuGaF6 (J/k = -71 K for the powder) is distinguished this way from the chain structure compounds KCuA1F(6) and Na2CuScF7 (J/k = -76 resp. -59 K) which were also magnetically studied and yield similar antiferromagnetic exchange constants J/k.

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AbstractBei der Darstellung von BaMnAlF7 erhielten wir als Nebenprodukt Einkristalle von Ba3Al2F12 (a = 1020, 3(2), b = 988, 5(1), c = 952, 2(1) pm, Raumgruppe Pnnm, Z = 4). Die erneute Verfeinerung bestätigte die schon bekannte Struktur, lieferte aber verbesserte Ergebnisse (R1′ = 0, 028 bzw. wR2 = 0, 06 für 1908 bzw. 2717 Reflexe), die hinsichtlich der Abstandsverhältnisse im tetrameren Anion [Al4F20]8— (Mittelwert Al—F: 180, 1 pm) gedeutet werden. Der Aufbau des kationischen Gerüsts [Ba3F2]4+ wird diskutiert.

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Single crystals of SrVF5 were obtained by heating a mixture of the component fluorides at 850 degreesC for 5 d (a = 707.2(l), b 727.1 (1), c = 1471.4(2) pm, beta = 94.96(l)degrees; space group P2(1)/c, Z 8). The X-ray structure determination confirmed its helical SrFeF5 type of chain structure, in which the octahedra sharing cis corners are considerably distorted (average V-F: 193,7 pm). The compound is weakly antiferromagnetic; there is indication of three-dimensional ordering only at the lowest temperature measured (T-N approximate to 2 K). The flat susceptibility maximum near 6 K is attributed to lowdimensional preordering. As studied at a single crystal the behaviour is anisotropic, indicating spin orientation about along [100], normal to the chain axis [010].

On the Crystal Structure of CaFeF5Single crystals of CaFeF5 were obtained by heating a mixture of the component fluorides at 860°C for 12 d (a = 549.2(1), b = 1007.6(2), c = 759.9(2) pm, β = 110.02(3)°; space group P21/c, Z = 4). The X‐ray structure redetermination of a twinned specimen confirmed the chain structure of octahedra sharing trans corners already known. But the anomalies reported earlier were removed and less distorted [FeF6] octahedra and [CaF7] pentagonal bipyramids were found, the distances of which are split within the usual range around mean values of Fe—F: 192.4 and Ca—F: 233.1 pm.

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The results of a single crystal X-ray structure determination of monoclinic (MeNH 3 ) 2 SiF 6 are reported: a = 962.3(5), b = 964.4(1), c = 966.4(5) pm, β = 100.03(3)°; V = 883.2(7) A 3 , Z = 4, space group C2/c; wR 2 = 0.0999 based on F o 2 of 1291 independent reflections (including H refinement without restrictions). The structure is related to that of (NH 4 ) 2 SiF 6 , but contains the dumb-bells of the cations well oriented along the greater cell diagonals and fixed by one nearly linear and two bi-furcated hydrogen bonds (N...F: 281 and 293 - 305 pm, resp.). The [SiF 6 -] 2 - octahedron is nearly undistorted with average bond length Si-F: 167.7 pm (169.9 pm corrected for thermal motion).

Studies to grow single crystals Of Cs2ZnCu3F10 (a = 715.9, b = 737.7, c = 943.6 pm, beta = 97.25degrees from powder data), deriving from CsCu2F5 by substitution, yielded as a by product crystals (of possibly zinc containing) Cs7Cu6F19 (a = 1559.3(3), b = 622.9(1), c = 1176.0(2) pm, beta = 99.05(3)degrees), at which a complete X-ray crystal structure determination was performed. Though most and all of the stronger reflections permitted refinement in space group C2/m of the Ba7Ir6O19 type, consideration of the weaker reflections confirmed the space group of the Cs7Cu6F19 type already known, but redetermined in P2(1)/a setting. With respect to the description in C2/m an average atom displacement of 6 pm resulted, only about a third of the amount of 16 pin for the structure documented in the literature. The Jahn-Teller distortion, possibly softened by partial Zn substitution, and the structural features are discussed.

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By solid state reaction of the component fluorides at elevated temperature single crystals of SrCaCrF7 were obtained (a = 792.3(2), b = 724.7(2), c = 986.1(2) pm; space group Puma, Z = 4). The X-ray structure determination confirmed isotypism with the Ca2AlF7 type of structure: Isolated octahedra [CrF6](3-) (mean Cr-F: 189.7 pm) are opposed by infinitely netted planar cations [SrFCa2/2](3+) which contain "independent" F atoms 3-coordinated by alkaline earth atoms only. The Sr atoms prefer (at a level of 80%) the 8-fold, the Ca atoms the 7-fold coordinated positions between the octahedra.

X-ray structure determinations of single crystals showed that compounds Cs2MCu3F10 crystallize with Z = 2 in space group P2(1)/n (No. 14) (M = Mn) of the CsCu2F5 type resp, in its super-group 12/m (No.12) (M = Mg, Co, Ni). Cs2MgCu3F10: a = 714.9(1), b = 736.8(1), c = 940.4(1)pm, b = 96.29(1)degrees, (Mg-F: 199.2 pm), Cs2MnCu3F10: a = 725.1(1), b = 742,7(1), c = 951.0(2) pm, b = 97.28(3)degrees, (Mn-F: 209.1 pm); Cs2CoCu3F10: a = 717.8(3), b = 739.1(2), c = 939.4(4) pm, b = 97.49(2)degrees, (Co-F: 203.1 pm); Cs2NiCu3F10: a = 716.3(1), b = 737.7(1), c = 938.2(2) pm, b = 97.09(1)degrees, (Ni-F: 201.0 pm). As determined directly for the Mg compound and generally concluded from the average distances M-F noted, M substitution concerns mainly the octahedrally coordinated position of the CsCu2F5 structure, the distortion of which is very much reduced thereby. Within the remaining [CuF4] and [CuF5] coordinations, in contrast to CsCu2F5, one F ligand is disordered, in case of the Mn compound the pyramidally coordinated Cu atom, too. The magnetic properties are complex and point to frustration and spin glass effects. Only at the diamagnetically substituted variants with M = Mg, Zn no Neel point appears, which is reached at 27, 23, 36 and 55 K for M = Mn, Co, Ni and Cu, resp.. At lower temperatures ferri- resp. weak ferromagnetism and hysteresis is observed.