worked out a new set of valence force constants from the vibrations of benzene and from the Coriolis zeta-coefficients, i n which a limited number of interaction constants were con- sidered on the basis of a hybrid orbital field of force. The resulting force constants agree closely with theoretical ex- pectations and may be applied to halogenated benzene deriva- tives as well as pyridine and its deuterium derivatives, with only minor modifications. - From the ground vibrations of molecules with a known geometrical arrangement Sawodny computed complete series of force constants of the general valence force model, by ascribing the vibrations, regarded as uncoupled, t o individual internal coordinates and thus obtaining solutions for the force constants, which are im- proved by gradual introduction of kinetic coupling according to the Newton method. This method yields good results if the normal vibrations are predominantly determined by

[VB 8121144 IE] single symmetry coordinates.

German version: Angew. Chem. 76. 616 (1964)

Recent Investigations into the Structures of Noble-Metal Compounds

K. Brodersen, Aachen (Germany)

Iridium(II1) chloride occurs as two modifications which differ in crystal form, color, and magnetic properties. Its mono- clinic modification forms platelets with the lattice constants: a = 5.99 A, b = 10.36 A, c = 5.98 A, and p = 109 "27'. The ar- rangement of atoms in the unit cell corresponds to that in aluminum(I1I) chloride, the parameters of the chlorine atoms being slightly different. Platinum(I1) chloride crystallizes in needle-like hexagonal prisms. Its rhombohedra1 unit cell has dimensions a = 8.09 8, and r. = 108 "15' and consists of six formula units. The lattice sites can be found from Weissenberg and precession photo- graphs; space group: D:,-C 3 m, lattice sites: 6 Pt on 6 (h): x = 0.079 and z = 0.333

6 CI on 6 (h): x = 0.583 and z = 0.825 6 CI on 6 (f): x = 0.258.

The six platinum atoms are arranged octahedrally with Pt-Pt distances of 3.32 8, or 3.40 8,. Each platinum is surrounded nearly quadratically by four chlorine atoms with Pt-C1 dis- tances 2.34 8, or 2.39 A. The 12 chlorine atoms are situated in front of the 12 edges of the Pt6 octahedron. Accordingly, platinum(I1) chloride has a structure with Pt6Cll2-complexes and with weak metal-metal bonds. [G DCh-Ortsverband Heidelberg (Germany), May 26th, 19641 [VB 823/146 IE]

German version: Angew. Chem. 76, (1964), in the press.

Size of the Solvation Sheath of Poly(viny1 alcohol) in Aqueous Solutions

S . Peter, Hannover (Germany)

The rheological properties of aqueous solutions of poly(viny1 alcohol) with molecular weights of 20000 or 85000 and 180000 were examined at 20- 50 "C and at concentrations up to about 10% by weight, using a Couette viscometer. The degree of hydrolysis of the products prepared by alkaline saponification of poly(viny1 acetate) was 98 %. The activation energy for the flow process was determined from the temperature depence of the viscosity in the absence of forces of interaction between the dissolved particles. At low concentrations, it corresponds to the activation energy for the flow of pure water. With increasing concentration, the activation energy rises and appears to approach a limiting value of about 6.2 kcal/mole. The effective, rheologically immobile volume proportion in the solution was determined using an expression proposed by Fmnck. With increasing dilution, the effective, rheologi-

Attgcw. Chem. intertiat. Edit. ] Vol. 3 (1964) 1 No. 7

cally immobile volume corresponding to unit weight of solute (denoted by ySp) tends to a limiting value pOsp which is proportional t o the intrinsic viscosity [7i] (cf. Table 1).

Table 1 . Limiting values 'pasp for c -f 0. at 20 "C.

I 1 Immobile wa'er 1

20000 14.7 85000 27.5

180000 i 39.8

36

19": 1 i::: 117.4

[a] Determined assuming the density of water in the salvation sheath to be equal to that of pure water.

The assumption that large solvation sheaths occur in aqueous solutions of poly(viny1 alcohol) is confirmed by the fact that [q] and pOsp decrease with increasing temperature, whereas [q] should increase with temperature if the solvent flows more or less freely through the poly(viny1 alcohol) coils. Thus, for polyisobutylene (mol. wt. 180000) in benzene, [q] has a value of 35.2 cm3/g at 24 OC and 76.5 cm3/g at 60 'C; poly(viny1 alcohol) with the same molecular weight, on the other hand, gave [q] = 119.4 crn3/g in water at 20 OC, and 99.0 cm3/g at 50 "C. [GDCh-Ortsverband Hannover (Germany), February 20th, 19641 [VB 806/142 IE]

German version: Angew. Chem. 76. 441 (1964)

Experiments with Potassium Needles

K. N2umann. GieDen (Germany) [l]

When potassium is sublimed onto wires of metals such as silver, gold, and platinum, moderate supersaturation leads to the formation of very fine needles with a thickness of a few hundred A and a length up to 1 mm. With suitable illumination, their diffraction diagrams can be observed as bright lines under the microscope, and their growth can be followed. At first, their length increases exponentially with time until a maximum constant rate of growth has been attained. This exceeds the value calculated for direct con- densation of the vapor on the growing tip by several powers of ten. Actually, potassium condenses on the long mantle faces and migrates from there along to the tip. Finally, the rapid lengthwise growth stops suddenly, and the needles begin instead to increase gradually in thickness, making it possible to recognize their shape: hexagonal (rarely quadratic) prisms with a roof formed from three or four (01 1) rhombs. The three long lateral faces are likewise (011) faces. The unimpeded growth a t the tip is probably due to a spiral dislocation terminating at this position. Observation of the rate of growth (or evaporation) as a function of the degree of supersaturation (or unsaturation) in the vapor phase also provides important information on the selfdiffusion of the K adatoms. Furthermore, the increase in vapor pressure of the needles owing to their low thickness is readily determined and from this in turn, the free sur- face energy of the (011) faces can be obtained, a magnitude which otherwise cannot be determined experimentally for solids. Its value is 170 +r 15 erg/cmz at 25 "C. With about 15-fold supersaturation in the vapor phase, rapid lengthwise growth stops as a result of two-dimensional nucleus formation on the side faces. If the supersaturation is reduced after some time, the needles again increase in length, but at a slower rate, because they have meanwhile become thicker. In this manner, the thickening can be followed in the critical region in which nucleus formation on the surface is

[ I ] Based on work carried out by F. Hock, W. Diftrnar, H. D. Meissner, and A . Kohler.

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