1656 Inovgunic Chemisiq, Vol. 9, N o . 7 , 1970
J . BRIANFAUGMT, THERALD MOELLER, AND IAIN C.PAUL CONTRIBUTION FROM W. .I.SOYES CHEXICAL LABORATORY, USIVERSITYOF ILLIXOIS, URBANA, ILLIXOIS 61801
The Crystal and Molecular Structure of Trimeric Phosphonitrilic Isothiocyanatel BY J. BRIAh' FAUGHT,2 THERALD MOELLER,
AND
I A I S C. PAUL3
Received September 8, 1969 T h e crystal structure of trimeric phosphonitrilic isothiocyanate, I\T3Ps( NCS)6, has been determined by three-dimensional single-crystal %-ray studies. T h e compound crystallizes in the triclinic space group P i with a = 11.79 (3), b = 8.02 ( 2 ) , c = 10.31 (1)A, a = 96" 0' (30'), P = 99" 4' (30'), -/ = 97" 28' (33'1, and two molecules per unit cell. T h e calculated density is 1.70 (2) g c m P ; the experimental density is 1.62 ( 8 ) g ~ m - ~T.h e structure was solved from 1246 independent nonzero reflections collected on film b y the Weissenberg technique and refined t o a conventional R factor of 0.12. T h e nitrogen atoms of two isothiocyanate groups are bonded t o each phosphorus atom in the six-membered phosphorus-nitrogen ring. Five of t h e atoms of t h e phosphonitrilic ri;g are planar, with the sixth atom, a nitrogen, 0.15 A out of the plane. T h e average P-N bond length ia the ring is 1.58 A with a root-mean-square deviation of 0.05 A ; the average P-N (exocyclic) bond length is 1.63 f 0.01 A. compared with the calculated value of 1.70 ( 2 ) g/cm2 assuming Introduction two molecules of KaPa(NCS)c (mol w t 483.43) in a unit cell of Timeric phosphonitrilic isothiocyanate was first prevolume 947 A3. T h e crystals are quite soluble in the liquids t h a t pared by Audrieth and c o ~ o r k e r s . The ~ ~ ~isothiocywe tried t o use for a density determination. T h e above value anate structure as opposed to the thiocyanate structure was obtained by partially saturating the solvent mixture and was assigned on the basis of the infrared s p e ~ t r u m . ~ carrying out t h e determination as rapidly as possihle. F ( 0 0 0 ) is 480, and the linear absorption coefficient for Cu K a radiation is Stahlberg and Steger6 made a detailed study of the 88.6 cm-I. T h e possible space groups are P1 or PT. Raman spectrum of this compound in solution and also T h e crystal selected for data collection had the dimensions concluded that the structural unit in this compound is 0.33 mm (along t h e a axis) and approximately 0 2 0 and 0.35 m n the isothiocyanate. They interpreted the spectrum in along the b and c axes, respectively. T h e crystal was mounted in a 0.5-rurn, thin-walled capillary which vias sealed at both ends, terms of D a h molecular symmetry. a s the crystals decompose after prolonged exposure t o the atCrystal and molecular structures have been reported mosphere. Multiple-film, equiinclination Weissenberg photofor several other trimeric compounds, including the graphs were taken with Xi-filtered Cu Kcr radiation in a cold room f l ~ o r i d e ,chloride,8, ~ and bromide, lo but no pseudomaintained a t 4 =IC2'. For the levels lkl through Qkl, two exhalide structure has been determined. This paper reposures were necessary t o record all the symmetry-nonequivalent data on the upper portion of the film. A total of 1246 indeports the results of a three-dimensional X-ray analysis pendent nonzero intensities were estimated by visual comparison on the structure of trimeric phosphonitrilic isothioof the reflections on t h e upper portion of the films with a series of cyanate. standard spots prepared from a specimen crystal. Lorentz,
Experimental Section Crystal Data and Data Collection.-Material suitable for singlecrystal studies was prepared from a solution of trimeric phosphonitrilic isothiocyanate in n-heptane at 0". A preliminary examination of a typical crystal using precession photographs indicated that i t belonged t o the triclinic system. A-0 systematic absences could be detected, and only Ci diffraction symmetry was noted. T h e unit cell dimensions, as measured from photographs taken on a 60-mm Buerger precession camera, equipped with Polaroid cassette, using Zr-filtered Mo K a radiation (X 0.7107 A) at 25', are as follows: a = 11.79 ( 3 ) , b = 8.02 ( 2 ) , c = 10.31 (1) A, Q = 96' 0' (30'), p = 99" 4' (30'), 7 = 97" 28' (30'). The standard deviations result from a number of measurements of t h e reciprocal lattice dimensions. T h e density measured by flotation in a bromobenzene-iodobenzene mixture is 1.62 (8) g!cm3,
a
(1) Supported in part by N I H Grants GLI 11996 and G M 12470. (2) Gulf Oil Gorp. Fellow in Chemistry, 1968-1969. (3) Alfred P. Sloan Research Fellow. (4) R. J. A. Otto a n d L. F. Audrieth, J . Arne?. Chem. Soc., 80, 5894 (1958). (5) G. Tesi, R. J. A. Otto, F. G. Sherif, and L. F. Audrieth, i b i d . , 82, 528 (1960). (6) R. Stahlberg and E. Steger, S p e c h o c h i m . A c t a , P w i A , 23, 2185 (1967). , (1963). (7) M W. Dougill, J . Chpm. S O L . 8211 (8) A. Wilson a n d L). F. Carroll, i b i d . , 2548 (1960). (9) E. Giglio, Ric. Sci., SO, 721 (1960); F. Pompa and A . Ripamonti, ibid.. 29, 1516 (1959). (10) E. Giglio and I
