J . Phys. Chem. 1986, 90, 2052-2057
2052
previously observed for a H,Se-HDSe-DzSe mixture in CDC13 solution.25 A shift of -10.6 ppm/D has been estimated for H,Te.45
Conclusions (1) In solid 111 motions are essentially stopped below -77 K, with some indications of a slow motion beginning between 77 and 90 K. It has been suggested p r e v i o ~ s l ythat ~ ~ ~this motion is probably 2-fold C2axis flips, but the present results are insufficient to prove this. ( 2 ) The phase change between solids 111 and I1 shows some hysteresis. The line shapes in the supercooled region of phase I1 for both 2H and 77Seshow considerable motional averaging from the rigid line shapes seen in phase 111. It was not possible, however, to make a definite assignment to a specific motion; there are several feasible models. The change from this motion to the fast motion in phase I1 above the transition region must be associated with the phase change mechanism since it is not an activated process. (45) Jameson, C. J.; Osten, H. J. J . Am. Chem. SOC.1985, 107, 4158.
(3) In solid I1 above the transition region the 2H and 77Seline shapes both indicate rapid n-fold ( n 3 3) reorientation in the plane of the molecule. (4) Rotations in the solid I and the liquid are exceedingly fast with apparent activation energies of 3.5 and 3.4 kJ mol-'. It is highly unlikely that the rotations can be described by small-step rotational diffusion (Le., Hubbard relationship will not be valid). There is a large discontinuity in at the melting point while rJ is approximately continuous across the melting point. This behavior is reminiscent of that observed for phosphine. ( 5 ) The 77Sechemical shift shows typical variations with temperature and there are large discontinuities at the gas-liquid and liquidsolid I phase transitions. An extremely large 2H secondary isotope effect is observed for both the neat liquid and the solid I phase. Acknowledgment. R.W. wishes to thank NSERC for financial support and the Atlantic Regional Magnetic Resonance Center for spectrometer time. Registry No. H2Se, 7783-07-5; "Se, 14681-72-2; D2, 7782-39-0.
Characterization and Crystal Structure of the Dbodium Salt of
1,2-Carbodicyanocyclobuten-3,4-dlone Vilma Busetti Dipartimento di Chimica Organica, Universitd di Padova. I-351 00 Padova, Italy
and Bruno Lunelli* Istituto Chimico "G.Ciamician". Universitd di Bologna, and Istituto di Spettroscopia Molecolare CNR, I-401 26 Bologna, Italy (Received: October 28, 1985)
The title compound, CloN4O2Na2, crystallizes with four water and one-half p-dioxane molecules in the monoclinic system, space group P2,/c, with a = 10.569 (3), b = 22.636 (4), c = 7.031 (2) A, fi = 96.40 (0.05), Z = 4. In the unit cell the dianions form stacks in the c axis direction, which are completely enclosed by solvents molecules and Na' cations. In turn Naf cations are surrounded by nearly regular octahedra of oxygen and nitrogen atoms; these octahedra extend in nearly perpendicular polymeric chains, along a and c axes. The thermal decompositionof the crystal and a method of getting crystals of water-soluble substances are reported and discussed.
Introduction The title compound was first synthesized in 1967 by Sprenger and Ziegenbein;, recently, an alternative method was reported.2 A prominent feature of its organic part, the 1,2-carbodicyanocyclobuten-3,4-dione(CDCB, I) structure, is the unusual O=C-
C-C(CN
I II
l2
O=C-C-C(CN),
I compliance of its highest energy orbital, which can be doubly, singly, or unoccupied, giving a dianion, a radical anion, and an electron-poor neutral species, re~pectively.~*~ This fact, and the similarity of the structure with those involved in organic semic o n d u c t o r ~solar , ~ ~ ~energy converters,',* coordination compounds? and the existence of numerous analogues with different ring size and/or substitution1w13stimulated a comprehensive investigation of its physicochemical p r o p e r t i e ~ , ~of * ~which , ' ~ the knowledge of interatomic distances, crystal structure, and properties is an essential part. 'Caution: p-Dioxane is a possibly mutagenic compound, see J . Chem. Educ. 1983, 60, A228.
The preparation of a single crystal proved quite difficult, and was finally successful only by using as a solvent a mixture whose peculiar properties are discussed below, in order to extract a line ( 1 ) Sprenger, H. E.; Ziegenbein, W. Angew. Chem., Znf.Ed. Engl. 1967, 6, 553.
(2) Fatiadi, A. J. J . Res. Natl. Bur. Stand. 1980, 85, 73. (3) Lunelli, B.; Corvaja, C.; Farnia, G. Trans. Furaday SOC.1971, 67, 1951.
(4) Capobianco, G.; Farnia, G.; Gennaro, A,; Lunelli, B. J . Electroanal. Chem. 1982. 142. ~.201. ( 5 ) Le Coustumer, G.; Anzil, J.; Mollier, Y. J . Chem. SOC., Chem. Com~
~
m&.'1979, 353.
(6) Wudl, F. Acc. Chem. Res. 1984, 17, 227. (7) Forster, M.; Hester, R. E. J . Chem. SOC., Faraday Trans. I , 1982, 78,
_ -.,. 1 Ad7
(8) Piechowski, A. P.; Bird, G. R.; Morel, D. L.; Stogryn, E. L. J . Phys. Chem. 1984,88,934. (9) Schmidt, A. H. Synthesis 1980, 961. (IO) Fukunaga, T. J. Am. Chem. SOC.1976, 98, 610. ( 1 1 ) Himes, V. L.; Mighell, A. D.; Hubbard, C. R.; Fatiadi, A. J. J . Res. Natl. Bur. Stand. 1919, 85, 87. (12) Fatiadi, A. J. J . Org. Chem. 1980, 85, 1338. (13) Gerecht, B.; Kampchen, T.; Kohler, K.; Massa, W.; Offerman, G.; Schmidt, R. E.; Seitz, G.; Sutrisno, R. Chem. Ber. 1984, 117, 2714. (14) Corvaja, C.; Farnia, G.; Lunelli, B. J . Chem. SOC.,Faraday Trans. 2 1975, 71, 1293.
0022-3654/86/2090-2052$01.50/0
0 1986 American Chemical Society
Characterization of 1,2-Carbodicyanocyclobuten-3,4-dione
Figure 1. Infrared spectra of paraffin oil and hexachlorobutadiene mulls: lower full line, CDCBNa,; dotted line, sample with composition CDCBNa, 2H20; upper full line, CDCBNa2.4H20.0.5DX. Bands marked with an arrow are attributed to DX.
+
of methodology which should be of help in similar, difficult cases. In this paper we report and discuss the molecular and crystal structure of CDCBNa2 on the basis of X-ray diffraction, thermogravimetry, differential scanning calorimetry, and IR spectrometry.
Experimental Section Synthesis of CDCBNa2. Several runs carried out by the method of Sprenger' showed that it was essential to add the sodium alcoholate slowly, to keep its concentration low, otherwise the reaction product is an orange-brown rather than a yellow powder. Elemental analyses of the darker product showed only N about 1% low, but the IR spectra had weak absorptions at frequencies characteristic of the isomeric 1,3-carbodicyanocyclobuten-2,4-dione dianion.I3 The low N content was attributed to another impurity, analogous to that present in the similar tetracyanoquinodimethane (TCNQ) system.I5 The pure compound was obtained only by mbar) from the solvent removal (2 h at 100 OC under 2 X crystalline material described in the next section. Preparation of the Single Crystal. Suitable crystals grew by cooling in the atmosphere a nearly saturated solution of the crude synthesis product in 1:4 water-dioxane at 100 OC. Composition of the Crystals. The deep yellow elongated crystals turn opaque and lose weight upon exposure to air; the IR spectrum of their powder, upper full line in Figure 1, shows absorptions due to p-dioxane (DX) and water. Elemental analyses of several samples gave results in agreement with CDCBNa2.3.5-4 H20.0.5DX. The uncertainty in the water content was attributed to the fact that small solvent losses give large errors in the number of water molecules, whose molecular weight is sensibly lower than that of the other crystal components. Thus we turned to gas-phase chromatography with thermal conductivity detection, where water gives a large signal. Measurement of dimethyl sulfoxide solutions of the crystal and of calibrated water-DX mixtures carried out on a DAN1 3200 gas chromatograph equipped with a S E 550 column at the fixed temperature of 120 OC gave a clear indication of an 8:l water:DX mole ratio. Thus the crystal composition is CDCBNa2.4H20.0.5DX, in agreement with density measurements. IR Spectra, Thermogravimetry, and Differential Scanning Calorimetry. All IR spectra, inclusive of those shown in Figure 1, were recorded by a Perkin-Elmer 180 IR spectrometer in the constant energy mode; resolution was 1-3 cm-I. Thermogravimetric (TG) measurements were carried out with a Mettler TG 50 thermobalance controlled by a T A 3000 system of the same make. The sample was heated at a rate of 2 OC m i d in a controlled air stream a t atmospheric pressure. Differential scanning calorimetry experiments utilized a Mettler DSC 20 accessory controlled by a TA 3000 system. The sample, contained in a flat aluminum box with a hole, was heated at a (15) Suchanski, M. R.; Van Duyne, R. P. J . Am. Chem. SOC.1976, 98, 250.
The Journal of Physical Chemistry, Vol. 90, No. 10, 1986 2053 rate of 2 OC min-I. The temperature range was narrower than that of T G measurements because the latter indicated that above 200 "C some decomposition occurred. All the details of the TG and DSC curves are reproducible. The curves shown in Figure 2 refer to samples which had undergone minimum solvent loss with respect to the theoretical CDCBNa2.4H20.0.5DX crystal composition. They are yellow crystals and turn orange upon solvent loss of 1-5% with respect to the initial weight. X-ray Analysis. Intensity data were collected from a crystal 0.20 X 0.15 X 0.60 mm on a Philips PW four-circle diffractometer using Mo Ka (A = 0.71069 A) radiation monochromatized by a graphite plate, 0 - 20 scan mode, scan width 1.2O, speed 0.030' s-I, background measured for 7 s at each extremity, 2' I O 4 28O, two standard intensity and orientation reflections measured at 3-h intervals without significant variations. Unit cell dimensions derived from a least-squares refinement of 0 values of 20 high-angle reflections, no absorption correction. Of 3999 independent reflections, 1799 with I 2 3 4 4 were used for the structure determination. Rint= 3.06% for 298 reflections. In a first attempt to solve the structure by direct methods the E map showed only sodium atoms and some oxygen atoms of water and dioxane molecules. A subsequent Fourier synthesis calculated with their contribution revealed fragments of the organic dianion. The structure was refined by full-matrix least-squares methods with anisotropic thermal parameters, unitary weights. All hydrogen atoms were localized in a difference Fourier synthesis; they were isotropically refined. The final R value is 6.55%; in the last difference map the peaks ranged from 0.28 to -0.28 e A-3. Average and maximum shifts divided by error were 0.003 and 0.008, respectively. Atomic scattering factors were taken from ref 16; programs SHELX 76,'' ORTEP 11 76,'' and MULTAN 7819 were used. Crystal data: CloN4O2Na2.4H2O-O.5C4H8O2, Mw = 370.2, monoclinic, space group P 2 , / c , a = 10.569 (3), b = 22.636 (4), c = 7.031 (2) A, /3 = 96.40 (O.O5)O, V = 1671.6 (7) A3, Z = 4, d, = 1.471, d , = 1.479 g ~ c m -(by ~ flotation in a trichloroo ethylene-dibromomethane mixture), F(000) = 760, ~ ( M Ka) = 1.55 cm-I.
Results and Discussion Solvent Choicefor Crystal Growth. Many attempts to produce CDCBNa2 in crystalline form by using different solvents, their mixtures, cooling and evaporation of solutions, solvents interdiffusion, and temperature gradientsZo were all unsuccessful. Finally we tried the mixture DX-water, because (i) the former is not, but the latter is a very good solvent for CDCBNa,; (ii) they are reciprocally miscible in all proportions and have similar vapor pressures; (iii) the enthalpy change of mixing is very low in a concentration range around 0.46 mole fraction of DX ( ~ 4 : l DX-water) where it changes sign.2' Thus, should CDCBNa2 crystallize with solvent molecules, only slight thermal effects due to the solvents could disturb its molecular ordering. Furthermore, it is known that the frequency of the C H stretching band in the Raman spectrum of DX-water solutions is higher than that in pure DX (the opposite of the usual behavior), and that lines corresponding to pure DX are absent in such solutions,22indicating strong interactions, and an ordering of the molecules. The solutions are reported to be composed of microphases, of which the water-rich phase contains the DX in the water network cavities.23,24 Finally, recent research has shown that DX can enter ~~
(16) International Tables for X-ray Crystallography, Vol. IV; Kynoch Press: Birmingham, 1974; 2nd ed. (17) Sheldrick, G. M. SHELX Program for Crystal Structure Determination, University of Cambridge, England, 1976. (18) Johnson, C. K.ORTEP 11, a Fortran Thermal-Ellipsoid Plot Program for Crystal Structure Illustrations, Oak Ridge 1976. (19) Main, P.; Hull, S . E.; Lessinger, L.; Germain, G.; Declercq, J.; Woolfson, M. M. MULTAN 78, A System of Computer Programs for the Automatic Solution of Crystal Structures from X-ray Diffraction Data, Universities of York, England, and Louvain, Belgium. (20) Jones, P. G. Chem. Brit. 1981, 17, 222. (21) Goates, J. R.; Sullivan, R. J. J . Phys. Chem. 1958, 62, 188. (22) Rezaev, N. I.; Shchepanyak, K. Opt. Spectrosc. 1965, 19, 409.
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The Journal of Physical Chemistry, Vol. 90, No. 10, 1986
Busetti and Lunelli
TABLE I: Weight and Enthalpy Changes upon Heating the CDCBNa2.4H20.0.5DX Crystal weight loss, o/o
enthalpy change measd temp range, OC kcal
measd
calcd for loss of
re1 to theor compn
2H7O + 0.5DX 3H;O + 0.5DX 3.5H2O + 0.5DX 4 H 2 0 + 0.5DX
21.62 26.48 28.91 31.35
temp, O C
initial
adjusted
87 105 155 300
23.0 26.1 27.6 31.7
23.4 26.5 28.0 32.6
at A
B C
E
with respect to weight
50.8 10.5
50-105 105-155
TABLE 11: Atomic Fractional Coordinates ( X lo4, for H Atoms X lo3) and huivalent Isotropic Thermal Parameters (A*)'
It
Figure 2. Termogravimetric (full line) and differential scanning calorimetric (dashed line) curves of powdered CDCBNa2.4H20.0.5DX.
with water in inclusion compounds.2s The first time we allowed a hot saturated solution of CDCBNa2 in 4:l DX-water to cool we obtained good crystals. Then it was found that this happens most easily in a limited range of compositions around this value. Mixtures of several cyclic compounds with one or more oxygen
-
I
atoms in the ring (such as trimethylene oxide (CH2-CH2-C-
,
i
H,-0), dioxolane (CH2-0-CH2-CH2-0), 1,3-dioxane, tetrahydrofuran26)and water show the same, infrequent enthalpy vs. composition pattern as DX-water. Trimethylene oxide and 1,3dioxane are known to give clathrate structures with water. Then it is our opinion that when a water-soluble substance does not give easily satisfactory crystals, it may be of help to use as a solvent a mixture of water and one of the cyclic compounds just listed. Stability and Thermal Behavior of CDCBNa2-4H20.0.5DX. The first result of the T G experiment, see Figure 2, was the nonzero slope of the curve at 30 OC, where the measurements started. In the 5 min required to bring the oven temperature from 20 (room temperature) to 30 OC, the sample lost 0.6% of its weight. Such ease of solvents loss, even at room temperature, accounts for the uncertainty in the number of water molecules evaluated from elemental analyses of the crystal (see Composition of Crystals Section). Joint examination of the TG and DSC curves of Figure 2 makes it apparent that points B and C of the former correspond to the end of endothermal processes, plausibly decompositions, whose enthalpy changes are reported in Table I. The weight loss at B is only 0.5% smaller than expected for the decomposition of CDCBNa2-4H20.0.5DX to CDCBNa,.H,O plus 3 mol of water and 0.5 mol of DX; at C it is 1.3% smaller than that calculated for decomposition to CDCBNa2-0.5H20plus 3.5 mol of water and 0.5 mol of DX. The theoretical initial weight can be evaluated by assuming that in B the weight loss is exactly equal to that calculated for the loss of 3 H 2 0 and 0.5DX; this is indicated by the dashed segment near the start of the T G curve. With this adjustment, the percent weight losses change slightly, as listed in Table I. Thus the existence of the phases CDCBNa2.H,0 and
(23) Naberukhin, Yu.I.; Shinskii, S. J. Zh. Struct. Khim. 1967.8, 606. (24) Gorbunov, B. Z.; Naberukhin, Yu.I. J . Mol. Srrucr. 1972, 14, 113. ( 2 5 ) MacNicol, D. D.; Mallinson, P.R. J. Inclusion Phenom. 1983, I , 169. ( 2 6 ) Morcom, K. W.: Smith, R. W. J . Chem. Soc., Faraday Trans. 1970, 66, 1073.
xla 2236 (2) 3525 (2) 4620 (3) 4530 (3) 6822 (5) 9901 (5) 9940 (5) 6811 (5) 5393 (5) 5360 (5) 6722 (5) 6734 (5) 7564 (5) 7576 (5) 7124 (5) 8864 (5) 8882 (5) 7140 (5) 2126 (4) 2331 (4) 4015 (4) 4316 (4) 1274 (4) 441 (8) 593 (7)
Ylb 2357 (1) 42 (1) 1419 (2) 2858 (2) 4016 (2) 2808 (2) 1414 (2) 296 (2) 1822 (2) 2473 (2) 2469 (2) 1841 (2) 2935 (2) 1373 (2) 3530 (2) 2855 (2) 1417 (2) 778 (2) 1813 (2) 1772 (2) 964 (2) 314 (2) 158 (2) 394 (4) -5 ( 5 )
156 (5) 249 (5) 168 (5) 297 (5) 441 (5) 433 (5) 397 (5) 461 ( 5 )
167 (2) 146 (2) 160 (2) 161 (2) 94 (2) 124 (2) 16 (2) 65 (2)
ZIC
296 (3) 852 (3) 6196 (6) 5988 (6) 5421 (8) 4859 (9) 4980 (9) 5632 (8) 5995 (7) 5916 (7) 5653 (7) 5696 (7) 5471 (7) 5515 (7) 5446 (8) 5139 (8) 5224 (8) 5601 (8) 3105 (6) -2376 (6) 2256 (6) -2017 ( 5 ) 146 (8) 1373 (13) -1682 (12) 328 317 -271 -242 311 147 -289 -243
Be, 3.53 (6) 3.23 (6) 3.2 (1) 3.3 (1) 3.8 (1) 4.3 (1) 4.9 (1) 3.9 (1) 2.2 (1) 2.2 (1) 2.1 (1) 1.9 (1) 2.3 (1) 2.4 (1) 2.6 (1) 2.9 (1) 2.8 (1) 2.7 (1) 4.0 (1) 4.3 (1) 4.2 (1) 3.4 (1) 5.8 (2) 6.8 (3) 6.8 (3)
(8) (8) (8) (8) (8) (8) (8) (8)
'Estimated standard deviations are in parentheses CDCBNa2.0.5H20 appear to be reasonably certain. Things are different at point A. Here the weight loss is higher (instead of lower) than expected for the loss of 2 H 2 0 and 0.5DX, the slope does not go to zero, and the DSC curve does not show the end of a process. However, we cannot exclude the existence of a CDCBNa2.2H20 phase, because the lack of a horizontal region in the TG curve may depend on the slowness of the process H 2 0 CDCBNa2.H20 relative to the CDCBNa2.2H20 heating rate; the pattern of the DSC curve may originate from the instability of the CDCBNa2.2H20phase, which under these conditions decompose together with its antecedent CDCBNa,. 2H20-0.5DX. For this reason we are now trying to study the system formed by CDCBNa2 and water only. At point D of the T G curve the weight loss is lower than expected for removal of all water and DX; in E it is higher, but with appreciable decomposition, because the residue of the experiment is a dark grey rather than a yellow powder and its IR spectrum is different from that of pure CDCBNa,, especially for the presence of medium-intensity absorptions in the OH stretching region, 3650-3200 cm-I. Thus, the water cannot be removed completely from the crystal by heating alone. Pumping alone will also not remove the water, because the weight loss of the pulverized crystals at 20 OC toward a liquid nitrogen cooled wall under a total pressure of 2 X mbar was 19% after 2 h and 21%, corresponding to the composition CDCBNa2.2H20,after 14 h.
-
+
Characterization of 1,2-Carbodicyanocyclobuten-3,4-dione
The Journal of Physical Chemistry, Vol. 90, No. 10, 1986 2055
TABLE 111: Least-Squares-Plane Equations through Asterisked Atoms, Referred to a ,b.c * Axes, and More Significant Torsion Andes
Plane 1. -0.1 337x - 0.031 l y - 0.99052 = -4.9701 C(7) 0.003 (6) C(1)* -0.006 ( 5 ) C(8) 0.014 (6) C(2)* 0.006 (5) C(9) 0.055 (6) C(3)* -0.007 (5) C(10) 0.089 (6) C(4)* 0.007 (5) N(1) 0.029 (6) O(1) -0.006 (4) N(2) 0.062 (6) O(2) 0.047 (4) N(3) 0.072 (6) C(5) -0.034 (5) N(4) 0.148 (6) C(6) 0.044 (5)
Nal
03
Plane 2. - 0 . 1 7 4 0 ~- 0 . 0 7 0 2 ~- 0.98222 = -5.5371 C(5)* 0.000 (5) N(1)* -0.002 (6) C(7)* 0.003 (6) NU)* 0.002 (6) C@)* -0.003 (6) Plane 3. - 0 . 1 4 7 2 ~+ 0 . 0 1 5 6 ~- 0.98902 = -4.8807 C(6)* 0.003 (5) N(3)* 0.000 (6) C(9)* -0.001 (6) N(4)* 0.005 (6) C(lO)* -0.008 (6) L12 = 3.3 (2)'; L13 = 2.8 (3)'; L23 = 5.2 (3)' Torsion Angles, deg 0(2)-C(2)-C( 1)-O( 1) C(3)-C(Z)-C( 1)-O( 1) C(3)-C(2)-C( I)-C(4) O( 1)-C( 1)-C(4)-C(6) C(3)-C(4)-C(1)-0(1) C ( l)-C(4)-C(6)-C(9) C ( 1)-C (4)-C(6)-C ( 10) C(2)-C( 3)-C( 5)-C(7) C ( 2)-C( 3)-C(5)-C(8)
-1.7 (5) -179.9 (5) -1.0 (5) 1.0 (5) -180.0 (5) -180.0 (5) 0.6 (5) -2.7 (5) -177.2 (5)
11s 6
A13
Figure 3. ORTEP 11 plot with numbering scheme and bond distances and angles. Esd's for the organic dianion range from 0.006 to 0.008 A, and from 0.4 to 0.5'; for dioxane the values are 0.009 A and 0.6'.
TABLE IV: Hydrogen Bonds, Symmetry Code as in Figure 6.
0 - H ...X, deg 144 (5) 143 (5) 159 (5) 151 (5) 156 (5) 129 (5) 150 (5)
0 - H ...X 0 ~ ( 2 . 1 ) - H ( 2 ) 0 ~ ( 2 . 1. . .)I O(2) O ~ ( l . l ) - H ( l ) O ~ ( l .... l Ow(2.1) )
0-H O...X 0.92 (6) 2.883 (6) 0.71 (6) 2.881 (6) 0~(2.2)-H(2)0~(2.2),..~~~0(1) 0.88 (5) 2.833 (6) 0 ~ ( 1 . 2 ) - H ( 2 ) 0 ~ ( 1 . 2...V'lO(l) ) 0.77 (5) 2.836 (6) O ~ ( l . l ) - H ( 1 ) 0 ~ ( 1 . 1...V"'N(3) ) 0.71 (5) 2.928 (7) 0 ~ ( 2 . 2 ) - H ( l ) O w ( 2 . 2 ... ) 'N(4) 0.77 (6) 3.018 (6) 0 ~ ( 1 . 2 ) - H ( 1 ) 0 ~ ( 1 .. .2. I)'N(3) 0.80 (6) 3.074 (7)
The IR spectrum of the latter is the dotted line in Figure 1 which shows the presence of both hydrogen-bonded and free O H groups. Pure anhydrous CDCBNa2 was obtained by shortly heating CDCBNa2.4Hz0.0.5DX under vacuum, as detailed in the Preparation of the Single Crystal section. The IR spectrum, lower full line in Figure 1, shows no absorption in the O H stretching region. Molecular Structure from X-ray Diffraction. Final atomic coordinates are listed in Table 11; bond distances and angles are shown in Figure 3. The ring is planar: the atoms directly attached to it, 0(1), 0 ( 2 ) , C(5), and C(6), are placed alternatively slightly above and below the plane defined by the ring, while the four C and four N atoms which make up the cyano groups and are the farthest from the ring are on the same side with respect to the ring plane. However, the deviations (Table 111) are small, entirely within the usual deviations of an intrinsically planar system to allow the whole crystal to attain an energy minimum. The distances C(l)-C(2), C(2)-C(3), and C(4)-C(1) may be considered equal and averaged to 1.468 (6) A, while C(3)-C(4), 1.422 ( 6 ) A, is remarkably shorter, indicating a significant residual' double bond character. In the squaric acid crystalz9the distances equivalent to our C(l)-C(4) and C(2)-C(3) are essentially equal, 1.458 (3) and 1.454 (3) A, but the double bond is shorter (1.405 (3) A) and the opposite bond longer (1.496 (3) ~
~~
~
~
~~
N2
~~
(27) Bertie, J. E.; Jacobs, S . M. J . Chem. Phys. 1978, 69, 4105. (28) Davidson, D. W.; Gough, S . R.; Lee, F.; Ripmeester, J. A. Rev. Chim. Miner. 1977, 14, 441 (29) Wang, Y . ; Stucky, G. D.; Williams, J. M. J . Chem. SOC.,Perkin Trans. 2 1974, 35.
A). The conclusions of this comparison agree with those drawn from ESR measurement^,^ chemical behavior,' ahd the abovementioned planarity of the CDCB structure. all of which indicate a rather spread out character for the a electrons. One would expect an even larger spread in the nuclearly very symmetric 1,2,3,4-tetracarbodicyanocyclobutenedianion which, however, is so far from planarity13 to make a comparison with our case not very significant. Such a large effect seems to require the operation of other causes (such as the static Jahn-Teller effect) besides the minimization of the crystal energy. In fact, I3C N M R in solution30 shows the presence of two types of chemically nonequivalent nitrile groups. In our crystal the C(ring)-C(CN)2 distance averages to 1.396 (6) A, compared to 1.387 (4) A in the 1,3-carbodicyanocyclopentane-2,4,5-trione dianion" (11), 1.338 (4) A in the neutral charge-transfer partner l-carbodicyano-3,4-diethoxycyclopentane-2,5-dione31 (111), and 1.374 (3) A in solid TCNQ3z(IV). These values seem directly correlated with the total electron availability on the ring. The average C-CN and C=N distances in CDCB2-, 1.426 (6) and 1.145 (6) A, respectively, are similar to the 1.426 (6) and 1.142 (3) A of 11, the 1.446 (4) and 1.138 (3) %,of 111, and the 1.440 (4) and 1.140 (3) A of IV. Structures lacking of resultant negative charge, which is mainly located on the carbon atoms adjacent to the ring,3J3 have longer C-CN distances but shorter (CN)&-C(ring) bonds attributable to the greater electron affinity of the carbodicyano group compared to the rest of the molecular unit. The DX molecule is located at a center of inversion, has a chair conformation, and plays an essential role as a component of the crystal, as detailed in the next section. Bond distances and angles (See Figure 3) are slightly different from standard values33but in good agreement with those determined for the inclusion compound 2'-hydroxy-2,4,4,7,4'-pentamethylflavan-DX-~ater.~~ Blinka, T. A.; West, R. Tetrahedron Lett. 1983, 24, 1561. Doherty, R. M.; Stewart, J. M.; Mighell, A. D.; Hubbard, C. R.; , A. J. Acta Crystallogr., Sect. B 1982, 38, 859. (32) Long, R. E.: Sparks, R. A.; Trueblood, K. N. Acta Crystallogr., 1965, 18. 932. (33) Sutton, L. E., Ed.: Tables of Interaromic Distances and Configuration in Molecules and Ions; The Chemical Society: London, 1958.
2056
Busetti and Lunelli
The Journal of Physical Chemistry, Vol. 90, No. 10, 1986
Figure 4. Crystal packing for CDCBNa,.4H20.0.5DX. f
I
#N 2
;c
Figure 5. Stacking of title compound along the c axis.
Our crystal has stoichiometric composition without vacancies in the DX position; thermal analyses have shown that DX removal destroys the CDCBNa2.4H20.0.5DX phase. Bond lengths and angles in water molecules range from 0.70 (6) to 0.93 (6) i% and from 87 (5) to 119 ( S ) ' , respectively. Crystal Packing from X-ray Diffraction. As can be seen in Figure 4, in the unit cell there are two columns of CDCB2- dianions, related by a screw axis. Each column consists of planar dianions successively repeated by the c glide symmetry, nearly parallel to each other, tilt angle 3.6 (3)O, and to the ab plane, tilt angle 7.9 ( 3 ) O ; they are also nearly equally interspaced; the C( l ) - C ( l), C(2)-C(2), and C ( 1)-C(2) distances of molecules 'Iz and x, ' I 2- y , z - lI2,are quite equal. at x, f 2 - y , z Distances between atoms of stacking molecules are reported in Figure 5. The columns, which are a feature of electronic conductor precursors,6 are completely and compactly surrounded by sodium cations and oxygen atoms of water or DX molecules. In turn sodium cations are surrounded by six atoms at the vertices of nearly regular octahedra, sharing atoms 0 ( 2 ) , N(1), N(2), and N(4) of the CDCBZ- dianion (see Figure 6 ) . Adjacent octahedra centered on Na( 1) share the edge between the vertices at O(11) and "IO( 12), forming infinite chains ex-
+
2.501
CL'
2.312
Syinrr,e t r y c o d e : no s y m b o l x
.Y
,z
I
X
,4-y
,4+7.-1
I1 111
x-1 -x+l -x+l -x+l
,+-y ,++2-1 ,-y ,-z+l , + + y - 1 ,+-7. ,-y ,- 2
X
,+-y I Y
IV V VI VI I VI11 IX
X
x-1 x-1
I I
y y
r++z
, z+l r
Z
, 2-1
Figure 6. Environment of Na' cations.
tending along the c axis; successive octahedra are connected to successive CDCB2- dianions of the same column. These chains
J. Phys. Chem. 1986, 90, 2057-2060 of octahedra repeat by translation along the a axis; octahedra of the same height of adjacent chains are connected through O(2) and N(2) of the same CDCB*-dianion (see Figures 5 and 6). Octahedra centered on Na(2) are symmetric with respect to the centers of symmetry and occur in pairs, sharing the edge between the vertices at 0(22), and ‘O(22). Together with the DX molecules they form infinite chains extending along the a axis. These chains repeat by translation along the c axis; adjacent chains are connected through N(1) and N(4) of two CDCB2- dianions related by the c glide symmetry. On the whole the crystal may be considered a giant molecule consisting of stacks of CDCB2- dianions fully dipped into an extended network of hydrogen bonds (see Table 111).
2057
Acknowledgment. The authors are indebted to Quinto L. Mulazzani for the gas chromatographic analyses and to Rosa Simoni and Giancarlo Fini for the thermal measurements. Partial financial support from the Minister0 della Pubblica Istruzione, fondi 60%, and from the Istituto di Spettroscopia Molecolare del CNR, Bologna, is acknowledged. Registry No. CDCBNa2-4H20.0.SDX, 100112-33-2.
Supplementary Material Available: A listing of observed and calculated structure factor amplitudes and thermal parameters of non-hydrogen atoms (13 pages). Order information is given on any current masthead page.
Ab Initio Molecular Orbital Calculations on “Isolated” Vibrational Frequencies in AMe, Radicals and Radical Ions (A = B-, C, N’, AI-, Si, P’) Ian Carmichael Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556 (Received: October 29, 1985)
A linear correlation is found between ab initio estimates of the C-H bond lengths in AMe, radicals and radical ions (A = B-,C, N+, Al-, Si, P+) and the theoretically derived harmonic frequenciesfor deuterium-isolated C-H stretches. SCF molecular orbital calculations within the unrestricted Hartree-Fock approximation employing a split-valence basis set coupled with an analytic second-derivative procedure for force constants are used to obtain these frequencies. The calculated data are scaled to experiment by comparison with the well-characterized isolated vibrations in trimethylamine, trimethylphosphine, and trimethylborane. After scaling, relatively accurate predictions are possible for the so far unobserved isolated C-H vibrations in the AMe3 species listed above. For the substituted tert-butyl radical, absorptions in the vicinity of 2825 and 2905 cm-I are expected. The corresponding pair in the trimethylaluminum molecule should lie around 2890 and 2940 cm-I. For the systems considered, the C-D stretches for monodeuterated radicals and the C-Mu stretches for muonium-containingradicals are also isolated and can be estimated by another simple scaling argument. The preferred site of (formal) muonium replacement has been identified and estimates of the parameters in a simple expression for the dihedral-angle dependence of the proton (or muon) hyperfine splitting constant have been derived.
Introduction Recently the frequencies of a number of “deuterium-isolated” C-H stretching vibrations for simple alkanes have been recorded in the gas phase by Raman spectroscopy.’ For molecules in which all but one hydrogen have been replaced by deuterium the C-H stretching mode, v& is uncoupled from other vibrations and thus localized, hence the term “isolated”. Further a strong linear correlation was found between these frequencies and the corresponding C-H bond length, r,(CH), calculated by a b initio techniques2 Such a linear correlation between v& and experimentally derived bond lengths, r,(CH), has also been r e p ~ r t e d ~for- ~a wide range of organic molecules. In addition, the effect of other substituents such as methyl groups, halogens, or lone pairs on the theoretically determined bond lengths of adjacent C-H bonds has been d i ~ c u s s e d . Potential ~,~ applications of these correlations in support of microwave studies and structure-reactivity models are numerous. In the course of a recent theoretical investigation into the electronic structure of the tert-butyl radical and several analogous ( 1 ) Snyder, R. G.; Aljibury, A. L.; Strauss, H. L.; Casal, H. L.; Gough, K. M.; Murphy, W. F. J . Chem. Phys. 1984,81, 5352. (2) Snyder, R. G.; Aljibury, A. L.; Strauss, H. L., cited in ref 1 . (3) McKean, D. C.; Duncan, J. L.; Batt, L. Spectrochim. Acta, Part A
-. - - .
1973. 29. 1037. .. --- .
(4) McKean, D. C. Chem. SOC.Reu. 1978, 7 , 399. (5) McKean, D. C.; Boggs, J. E.; Schaffer, L. J . Mol. Struct. 1984, 116, 313.
0022-3654/86/2090-2057$01 S O / O
species a similar correlation has been uncovered between the ab initio optimized C-H bond lengths and the theoretically derived harmonic frequencies, -@, for the isolated stretching modes. This is a special case of the more general linear relation noted by Defrees et aL6 between computed values of r,(CH) and calculated C-H bond stretching force constants. In view of the above results, the existence of such a relation, reminiscent of Badger’s rule,’ is perhaps not surprising. However, the precision with which the linear relation holds for the AMe, species offers a simple method for the prediction of various isotopic “isolated” frequencies such as those pertaining in AMe2CH2Dand AMe2CH2Mu. While the modes in the latter group of molecules will not be observable by the conventional techniques of vibrational spectroscopy, an indication of their magnitude provides useful structural guidelines concerning, for example, specificity in substitutional sites. From electron spin resonance8 and muonium spin rotationg measurements the isotropic hyperfine coupling constants, aiso,and their temperature dependence, dlal/dT, have been recorded for CMe,, CMe2CHzD, and CMezCHzMu. The differences in dlal/dT among the isotopic species (regarding muonium as a light isotope of hydrogen of mass about mH/9) are obviously related to the characteristic vibrational amplitudes of each substituent. (6) Defrees, D. J.; Hassner, D. Z.; Hehre, W. J.; Peter, E. A,; Wolfsberg, M. J . Am. Chem. SOC.1978, 100, 641. (7) Badger, R. M. J . Chem. Phys. 1934, 2, 13; 1935, 3, 710. (8) Burkard, P.; Fischer, H. J . Mugn. Reson. 1980, 40, 335. (9) Roduner, E.;Strub, W.; Burkard, P.; Hochmann, J.; Percival, P. W.; Fischer, H.; Ramos, M.; Webster, B. C. Chem. Phys. 1982, 67, 275.
0 1986 American Chemical Society
