Band 210, Heft 11

Bond valence analysis has been performed on crystalline elements which occur in different modifications. For this purpose, the covalence of elements of main groups I to IV is set equal to group number N and to 8- N for elements of groups V to VIII. For d - and f -elements, empirical relations between melting temperature, atomic volume, and covalence were established and used for calculating the covalences. Bond valence parameters are calculated for 19 elements using the concept of geometrical coordination which applies equally well to primary and secondary bonds.

Simple mathematical functions have been found that describe such fundamental structures as primitive packings, closest packings and body centred packing of atoms. Functions for chemical structures like diamond, cristobalite, zincblende, CsCl, CaFe 2 , ReO 3 , and sodalite are given. The concept of mathematical dynamics is defined, and used to describe how surfaces are related to structures.

The high temperature modification of η -Cu 6 Sn 5 (reassigned η -Cu 5 Sn 4 ) was by means of electron diffraction found to exhibit structural modulations. The diffraction patterns may be indexed using the basic NiAs-cell and a modulation vector q ≈ ( δ a * /24, δ a * /24, c * /2), 8 ≤ δ ≤ 9. Models for the crystal structures of the two commensurate modulations δ = 8 and δ = 9 are suggested. Both superstructures are caused by the ordered occupancy of Cu in the trigonal bipyramidal sites. The model given for η 6 -Cu 5 Sn 4 (corresponding to δ = 8, found above 350° C) has the space group C 2 and cell parameters a = 12.60 Å, b = 7.27 Å and c = 10.20 Å and β = 90.0°. η 8 -Cu 5 Sn 4 , corresponding to δ = 9, has the unit cell (in P 2 1 / c ) a = c = 9.83 Å, b = 7.27 Å and β = 62.5°.

A calcium nickel orthophosphate complex has been isolated and shown to display a solid state structure similar to that of α -Ca 3 (PO 4 ) 3 with columns of cations surrounded by (PO 4 )-nickel-(PO 4 )-vacancy columns in hexagonal array. Calcium and nickel atoms are distributed within the cation columns. Ca 8.5 Ni 9.5 (PO 4 ) 12 (space group C 2/ c , a = 22.819(5) Å, b = 9.944(2) Å, c = 16.982(3) Å, β = 99.97(3)°, D calc = 3.67gcm −3 , Z = 4, R = 5.59% for 3216 obs. refls.) shows cation columns to contain 29.2% nickel and 70.8% calcium atoms.

NaNO 3 , R[unk] c , a = 5.0701(2) Å, c = 16.822(2) Å, V = 374.4 Å 3 , Z = 6. Neutron diffraction: λ = 0.87013 Å, μ = 0.1 cm −1 , F (000) = 182.1 fm. The intensities are checked for normal and independent distribution and their Poisson variances are modified with the aid of χ 2 values of repeatedly measured intensities. Refinement on | F | 2 including weak and negative intensities. Anharmonic motion of N and O up the third order of a Gram-Charlier expansion was refined. R = 0.032, wR = 0.026, S 2 = 1.99, 3642 measured and 317 unique intensities, 17 parameters. Synchrotron X-ray diffraction: λ = 0.56 Å, F (000) = 78 e , refinement on | F |. Anharmonic motion of N and O up to the fourth order of a Gram-Charlier expansion was refined. R = 0.020, wR = 0.007, S 2 = 1.51,443 unique intensities, 39 parameters. No ±180° Ising-type in plane orientational disorder of NO 3 -groups is observed at 293 K. Multipolar expansion of the electron density reveals bonding electrons and a strong deformation of the atoms within the planar NO 3 -group.

Ag 4 GeO 4 was synthesized by solid state reaction of the binary components applying high oxygen pressure and water as an accelerating agent. Ag 4 GeO 4 crystallizes triclinic ( P [unk], Z = 4, a = 6.4099(8) Å, b = 8.5122(10) Å, c = 10.0891(14) Å, α = 106.91(1)°, β = 92.19(1)°, γ = 95.80(1)°, V = 522.66(12) Å 3 , conventional R = 8.29%). Crystals of Ag 4 GeO 4 show systematic twinning with the twinning plane (014). The crystal structure of Ag 4 GeO 4 consists of tetrahedral orthogermanate ions, which are surrounded by silver cations forming a cuboctahedron. All cations together (Ag + and Ge 4+ ) constitute a distorted ccp structure. The twinning of Ag 4 GeO 4 is accountable to this cationic arrangement.

The 1-ethyl-2, 6-dimethyl-4(1 H )-pyridinone, trihydrate C 9 H 13 NO · 3H 2 O (EDMP) is a potential nonlinear optical crystalline material for second harmonic generation till the near ultraviolet region, crystallizing in the monoclinic space group Cc with Z = 4 and the unit cell parameters a = 8.382(1) Å, b = 19.275(2) Å, c = 7.220(3) Å, β = 104.56(2)°. The crystal structure was solved by direct methods and refined by least squares to R = 0.026 using 862 non equivalent reflections. EDMP molecules lying in planes parallel to (001) are linked through O–H---O and C–H---O bonds with the water molecule network. Layers are built from adjacent five and seven-membered rings of the water molecules and EDMP oxygen atoms forming a semiclathrate structure.

A series of C-3 substituted 4-amino-( D 3 )-trishomocubanes with promising antiparkinsonian and antiviral activities has been recently synthesized via a modified Ritter reaction. The crystal structure of one of these compounds, the 3-methyl-( D 3 )-trishomocubane-4-amine hydrochloride hydrate (C 12 H 18 N + Cl − · H 2 O) has been determined by X-ray diffraction. The symmetry is monoclinic, space group P 2 1 / c with a = 6.500(1) Å, b = 7.038(2) Å, c = 25.686(7) Å, β = 91.51(1)°, Z = 4. The 3 S 4 S /3 R 4 R stereochemistry is in favor of a one step rearrangement mechanism of the SN 2 type for the synthesis of ( D 3 )-trishomocubanes via the Ritter reaction.

(1,1′-Ferrocenediyl)di- n -butylsilane, C 18 H 26 FeSi, ( 1 ) is a symmetrically substituted [1] ferrocenophane. The crystal structure of 1 , determined from single crystal X-ray diffraction data, is in the monoclinic space group P 2 1 / c with a = 19.721(2) Å, b = 9.785(1) Å, c = 8.840(2) Å, β = 101.11(1)°, Z = 4, D calc = 1.295 Mg · m ′3 , F (100) = 696, T = 136 K, R = 0.026 for 2991 reflections with F 2 > 2 σ ( F 2 ). The two n -butyl substituents of the molecule are both disordered over two sites. The cyclopentadienyl rings tilt by 19.35(10) Å towards the Si atom as a result of molecule strain.

The crystal structures of three compounds of the general formula R 2 P(Se)C(S)N(H)R′ have been determined at room temperature. The green crystals of [Ph 2 P(Se)C(S)N(H)Me], C 14 H 14 NPSSe, are triclinic, space group P [unk] with unit cell dimensions a = 12.511(3) Å, b = 13.298(3) Å, c = 10.178(3) Å, α = 109.28(2)°, β = 103.25(2)°, γ = 66.94(2)°, Z = 4 and D x = 1.538 Mg m −3 . The yellow crystals of [ c Hex 2 P(Se)C(S)N(H)Me], C 14 H 26 NPSSe, are orthorhombic, space group Pnma with unit cell dimensions a = 10.299(2) Å, b = 15.384(2) Å, c = 10.344(2) Å, Z = 4 and D x = 1.420 Mg m −3 . The yellow crystals of [ c Hex 2 P(Se)C(S)N(H)Ph], C 19 H 28 NPSSe, are triclinic, space group P [unk] with unit cell dimensions a = 9.738(2) Å, b = 11.248(2) Å, c = 9.406(1) Å, α = 100.72(1)°, β = 104.84(1)°, γ = 83.58(1)°, Z = 2 and D x = 1.403 Mg m −3 . The structures were solved by direct methods and refined by a full-matrix least-squares procedure to final R = 0.038 using 2097 reflections for [Ph 2 P(Se)C(S)N(H)Me], R = 0.034 using 1180 reflections for [ c Hex 2 P(Se)C(S)N(H)Me], and R = 0.033 using 2508 reflections for [ c Hex 2 P(Se) · · C(S)N(H)Ph]. The conformation about the C(1)–N(1) bond in all three structures is Z . Differences in the P(1)–C(1) and C(1)–N(1) bond distances in a series of R 2 P(Y)C(S)N(H)R′, Y = 0, O, S, or Se, R = Ph or c Hex and R′ = Ph or Me, compounds are correlated with the nature of the phosphorus- and nitrogen-bound substituents, respectively.