The crystal structure of urea oxalic acid, 2[CO(NH2)2].(COOH)2 has been determined using three-dimensional X-ray data, collected on an automatic diffractometer. The space group is P21/c. The lattice constants are: a = 5.058 (3), b = 12.400 (3), c = 6.964 (2) A, fl= 98"13 (7) °. The number of molecules in the unit cell is two. The structure consists of layers of urea and oxalic acid molecules held together by hydrogen bonds. The positions of all hydrogen atoms have been found. The compound is not a uronium salt

Bats, J.W.

Feil, D.

Harkema, S.

Weyenberg, A.M.

English

University of Twente Research Information

1646 S H O R T  C O M M U N I C A T I O N S  Acta Cryst. (1972). B28, 1646 The crystal structure of urea oxalic acid ( 2 : 1 ) .  By S. HARKEMA, J.W. BATS, A. M. WEYENBERG* and D. FEIL, Chem- ical Physics Laboratory, Twente University o f  Technology, Enschede, The Netherlands. (Received I March 1971) The crystal structure of urea oxalic acid, 2[CO(NH2)2].(COOH)2 has been determined using three-di- mensional X-ray data, collected on an automatic diffractometer. The space group is P21/c. The lattice constants are: a = 5.058 (3), b = 12.400 (3), c = 6.964 (2) A, fl= 98"13 (7) °. The number of molecules in the unit cell is two. The structure consists of layers of urea and oxalic acid molecules held together by hydrogen bonds. The positions of all hydrogen atoms have been found. The compound is not a uronium salt. Introduction The structures of protonated urea and thiourea cations have been investigated in recent years by a number of methods. These techniques include infrared spectroscopy (Janssen, 1961; Kutzelnigg & Mecke, 1961), nuclear mag- netic resonance (Stewart & Siddall, 1970), X-ray and neu- tron diffraction. The work done on uronium nitrate by the last two methods (Harkema & Feil, 1969; Worsham & Busing, 1969) shows that the extra proton is attached to the oxygen atom of urea and that measurable changes in geom- etry occur when urea is protonated. The same applies to the structure of N-methyluronium nitrate (Bryden, 1957; Selman & Harkema, 1971). As part of our investigations on bonding in urea compounds we decided to determine accurately the structure of urea oxalic acid. A preliminary report on the determination of this structure has been given by Schuch, Merritt & Sturdivant (1950). Experimental Crystals of urea oxalic acid (2: I) were prepared by evapo- ration of an aqueous solution of urea and oxalic acid in the stoichiometric ratio. The crystals formed in this way have a pronounced cleavage plane which indicates a two- dimensional hydrogen-bonding network. Data  were collected on a Nonius automatic diffractom- eter at room temperature. A crystal of size 0.3 x 0-2 x 0.2 mm was mounted with the b axis parallel to the goniometer axis. Reflexions with 0 < 35 ° were measured with Zr-filtered Mo K~ radiation (2=0-70926 A) using the 0-20 scanning technique. In this way 1058 independent reflexions were measured, each having an intensity greater than twice the corresponding standard deviation from counting statistics. The space group of the crystal is P21/c, in accordance with previous work (Lonsdale, 1941). The cell dimensions found are: a = 5.058 (3), b = 12.400 (3), c = 6"964 (2), fl = 98.13 (7) ° (here as in the rest of the paper the values given in brackets represent the standard devia- tion in the last decimal place of the number given). The number of molecules in the unit cell is 2, consisting of 2 molecules of oxalic acid and 4 molecules of urea (Lonsdale, 1941). From the very strong 102 reflexion it is clear that all molecules must be approximately parallel to the (102-) plane. No correction for absorption was applied (p=  1.3 cm-1). Structure determination As the general position in the space group P21/c is fourfold, the oxalic acid molecules must lie on centres of symmetry. * Present address: AKZO research, Amhem, The Nether- lands. With the help of the known molecular geometries, a model of the structure was constructed and rotated in the plane containing the molecules until an acceptable hydrogen bonding scheme was found. Coordinates for the heavy atoms obtained in this way were used as input for the least- squares program. The identity of the atoms in the urea molecule was established from the isotropic temperature factors resulting from refinement with one atomic form fac- tor (that of nitrogen) for all atoms. The weighting scheme used in the refinement was the same as that reported for uronium nitrate (Harkema & Fell, 1969). Four cycles of refinement with anisotropic tem- perature tactors gave an R factor of 7.1%. A difference Fourier synthesis made at this stage clearly revealed the hydrogen atoms. Inclusion of the hydrogen atoms and refinement of their positions and isotropic tem- perature factors, together with the positions and aniso- tropic temperature factors of the other atoms, gave a final R value of 4.0 %. In the last stages of refinement a secon- dary-extinction correction was applied (Zachariasen, 1963; Larson, 1970). Observed and calculated structure factors are collected in Table 1. Final positional parameters are given in Table 2. Table 3 shows the vibration parameters obtained from the least- squares analysis. The labelling of the atoms is given in Fig. 1, which shows a projection of the structure on the (102-) 201 .... \ "  211 ..-~ ,'~ / / C(2,) [ '~ . .  / i  , _ "c" ; ~ H(5) H'4" " : - ' - - % /  ) "  , ~ : r  0(2"9 \ ,~, N(1) " "  x - " " / -  " \  I ~ < . / - ; \  ~ ",!~!j_---<~o(" 3.) - \  / 0 ( 1 )  N ( 2 ) / ~ ' ~ : "  \. \ o(~))r,.o) ;~""(~) ~i-~ ) J  a ~ ;L,-~ o l o  Fig. I. Projection of the crystal structure of urea oxalic acid on (102-). The vibration ellipsoids of the heavy atoms are scaled to include 50% probability. The hydrogen atoms have ar- bitrary, small isotropic vibration parameters. S H O R T  C O M M U N I C A T I O N S  1647 Table 1. Observed and calculated structure factors ( x 1 O) for urea oxalic acid H K ,~ ro FC 1 -1  2 - i  . ~  0 i - i  5 0 -1 - 2  - i  5 0 c ro e= o 11o 111 ) 20 ;'~ o o .119 ) 0 9  ) i 2?5 289 115 I~2  I ?q ~1 o o Ia2 1)2 ] I 151 150 °° ' ,0 , °  ~ I 1°° , , I~ L o o ~o 0 0 62 60 | 1 ~? 20 ° °  S . . . . . . . .  o o 20 1 1 : o  18 o ~ . . . . . .  :~ . . . . . .  o 1o i  I75 111 112 0 2 ~ S  ~50 1 2 ~02 2 ° )  o~ . . . . . .  ~ . . . .  o 7 9 ;  2 116 1 o 2 2~ 25 ] 2 115 1 1 ]  c a. z ) 5O o z ]o I ?  z i ?  2~ o , 215 2 l  j 115 IA  c ,,i 2J5 ~ ~eo . . . . . . . .  ' ~ . . . . .  '-i : ',~ ',;~ C ~ 11½ 1 5 7  0 1 5 3,~ . '0 J .~ I~0 ~] 0C . 1 2 5 : i ~ d 2  -11 : 55 92°~ ( ~  -3.. ]1111 Ii~ x i ,x: , .  . . .  . i : " '  o 11 iz - J  11  11 o 52 J 91 6 12 ) I  9 I )  10 I 12 I,/ o @8 9q o ~ 1 i~ ~1., - s  1 5 I,, ~ i ,~ ~zq `)2? 6 5q eO - ,  ,~ 20 2O i , , i  , 6 t  86 es  s I ;  o 1 t I ! , x L ro r c  -s  i l 2 l  21 * i 2 i? -, ,~ :2 .... -o I e 1 o I ] I ~?  115 - ) 122 l z c  i ] 1211 121 - 2  ' ae J2 -5 -s  i 51 51 -(1 1 1 J6 J~ IO  11 1 J ", ', "~ ,~  '~d ; `)i? . . . . . . . .  . ~ c r o  rc . ~o ~ o i 2 i~ . i  - I  l ~ 2  2~2 o 2 i 2 65 5~ 2 ~ ,o, ,o5 -: ' IX ~ 2 2 2 )  . . . . . .  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' °  25 15 i' 16 z 6 i 108 to .  105  ~ 6 ) i' i! :i Z$ 26 -1 , ~ q5 5 el . 1  - 1  6 ~ e6 ,, ,~ -, ,; zn 14 o s 1~ a. 5 02 11 i e', .... ~ ! i ! "  5e  11 -~ 5 15  z ' ,  2 5 21 21 ,o .: ~ ; ~2 :2  s ~ i. ro r c  H ~ ~. vo r e  s x ~ ro rc , , 6 i ! ~ . . . .  i ....... ! ~ 15 } }  1 1:) 6 ~ ~ ~ J~ J~ o 11, - 1 I~  16 - ` )  15 - J - I  6 8 11 ? I -~ 7 ? I~  1% I I q 0 ~FI 9u - 5  10 . . . . . . . . . . . .  ?! 'ii i ii '° - i  ? o ,O l  '~9 2 : O ~00 9~ 8 l  al . ~ ,  ~ ,0 ,,,, - 1  ~ ~ 1 ,1  I J~  - 2  sa ' ?  . . . .  :i? - t  e Io. ,  s o ~ . . . . .  ' S o ~ 2u I ~ I 11~ 110 - ,  , 0 . . . .  ' ,  . , o. - I i  l 11 l~b ¢,5 . . . .  , : 11 . . . .  ) ,  21 1 o ~ 17 31  - J  ! 1o s .~ o ) I(,8 I?, I) 11 -1 : ', ',~ ',?, -~ ~ ', ~; ~,', - 5  ? ~ ~ .  ~,,, o o ~, 1 5 .  I~ -~  . . 105 0 ? `) 151 I R 0  2 0 2 t15 9 )  i ? .z 115 115  -a a i e5  ~1  tso 65 lg 111 o 52 "11 0, :g 1o I s  -~  a ~I o o 5 l  ~2 - I  ~ ~ ~0 61 1 o~ 0 g I <) I-) . . . . . . . . . . . .  'A , i  ? ~ 1 | 1  1 2 d  ") ~ • 11 21 ~ /  ~0 l h  15 - 1  `)~ ~ . . . .  1, o 9 `) 11 ¢) 111 1 IC - ~  99 ~ 51 ,'.10 - ]  1, 105 1o , ~ . . . . . . .  :o -~ i 1oi io~ ~ i e ,  a ,  5 I 0  i I ~ l t o  I ~  i . 1  i o  i o  i * i ~1 2,  I 1~ i - 1  ? 'i 5 "~ ' - I  q : i i  i ~o  ~62 2 ~o ~5 z 12u i z z  z o~ e~ a l J  ~)  z i . o  i ~  1 i z  l )  62 59 i 11o ,15 ~o , I c i  q~ 5 I , ,  ~ -a i?  1o 5 ~o i .  o 2 1~5 ~5 % '~ ) 51 q q  I - u  10 , ?,  ~, 1 "° 5, ) m5 ~s  ) Ib 11 o¥ 9 u 2 ]  2| e5 05 - z  ,, ~ ~I~ 1o ~,,g l o  I1 . ~ 1 -  ,0  0 "  !! o ns  ~,~ ~o ~, 712 127 Ig5 ILl I~I I.} ,, .... ,, :~ l ~ 05 l i~ 1 ,  ~a i o l  a ' ,  ;~} i: 21 11 2q ~ .  : 11 2~ u l  e o  ~ o  5 i ?  lO s 21 ~ ', J ,  i~  ~v, ?i 6 ~1 I*  - 5  6 ~ ~b  2 i  1 7 5 1 1 1  1 ( I  - ~  . ', 1.~ ' . ~  g • . '1  19  - 5  1 0  b 19  ,1  i i i  - ~  ? ~ . . , ,  ~1  i ,, . i . ,  i ,  - ,  ,~ ~ 1~  11 ] 1  1', 1~ I 1 $ 1 1 ' ,  I "  I 7 I i , "  2~ [ - I  15 ' ! i 5  ,o,,,: ' i " :  . . . . . . . .  ":;:, : } ? ? i l i i l 2 ! 2 :  ' i i ! ~ l i ! i ° i ~ :  ?? plane. This figure was prepared with the OR TEP-program (Johnson, 1965). Table 2. Final atomic parameters x/a y/b z/c N(I) 0"9970 (3) 0"1507 (2) 0"4857 (2) N(2) 0"6215 (3) 0-2136 (1) 0"3047 (2) O(1) 0"7033 (2) 0"0348 (1) 0"3319 (2) 0(2) 0-1552 (2) 0"1245 (2) 0"0388 (2) 0(3) 0"2864 (2) -0"0380 (1) 0-1502 (2) C(1) 0.7709 (3) 0.1307 (1) 0-3729 (2) C(2) 0.1237 (2) 0.0284 (1) 0-0517 (2) H(1) 0-446 (4) 0.002 (2) 0.211 (3) H(2) 0.475 (4) 0.201 (2) 0.227 (3) H(3) 0.680 (4) 0.278 (2) 0.319 (3) H(4) 0.049 (4) 0.213 (2) 0.513 (3) H(5) 0.090 (4) 0.095 (2) 0.537 (3) Discussion of the results The structure of urea oxalic acid consists of nearly planar urea and oxalic acid molecules held together by a two-di- mensional hydrogen-bonding network. The acidic proton is attached to the oxalic acid molecule. The compound, un- like uronium nitrate, is not a uronium salt. This difference may be related to the difference in acid strength between oxalic acid and nitric acid. The bond distances and angles found in the title com- pound are given in Tables 4 and 5 respectively. These geo- metric data are compared with the results of recent struc- ture determinations on related compounds. In accordance with the fact that the compound studied is an addition compound, differences in bond lengths and angles are very small when one compares the urea and oxalic acid mole- cules in this compound with urea and oxalic acid dihydrate. As usual, bond lengths involving hydrogen atoms deter- mined by X-ray diffraction are shorter than the ones deter- mined by neutron diffraction. This effect is due to the as- sumption commonly made in X-ray analysis that the elec- tron density of bonded atoms is spherically symmetric. A theoretical study of the geometry of the uronium ion and the urea molecule is in progress. References BRYDEN, J .  H .  ( 1 9 5 7 ) .  Acta Cryst. 10 ,  7 1 4 .  H A R K E M A ,  S .  • FELL, D .  ( 1 9 6 9 ) .  Acta Cryst. B 2 5 ,  5 8 9 .  JANSSEN, M. J. (1961). Spectrochim. Acta, 17, 475. JOHNSON, C. K. (1965). ORTEP. ORNL-3794, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 1648 S H O R T  C O M M U N I C A T I O N S  The temperature The temperature N(1) N(2) O(1) 0(2) 0(3) C(1) C(2) H(1) H(2) H(3) H(4) H(5) Table 3. Vibration parameters factor for the heavy atoms was: exp [-2rc2(h 2 a .2 Ull +2h k a* b* Uz2+ "" ")]. factor for the hydrogen atoms was: exp [ - ( B  sin 2 0/)~2)]. U11 U22 U33 0"0396 (6) 0"0312 (8) 0"0578 (10) 0"0480 (8) 0.0281 (8) 0"0635 (10) 0"0331 (5) 0.0257 (8) 0.0537 (7) 0.0377 (5) 0.0234 (8) 0.0602 (7) 0.0289 (5) 0.0288 (8) 0.0498 (7) 0"0317 (6) 0.0281 (8) 0.0347 (7) 0.0266 (5) 0.0257 (16) 0.0344 (7) 7"3 (6) 4.8 (4) 4-9 (5) 6"1 (6) 4"9 (5) Table 4. Bond distances (A) Oxalic acid Urea-oxalic acid dihydrate (a), (at), (g) (b), (e), (g) C(2)-C(2') 1.521 (5) 1.536 (3) C(2)-O(2) 1.209 (3) 1.212 (4) C(2)-O(3) 1.289 (5) 1.291 (5) O(3)-H(1) 0.96 (4) 1.026 (7) C(1)-N(1) 1.318 (6) C(1)-N(2) 1.321 (4) C(1)-O(1) 1-260 (3) N(2)-H(3) 0.86 (2) N(I)-H(4) 0.84 (2) N(2)-H(2) 0.86 (4) N(1)-H(5) 0"88 (3) O(1) ' ' -  0(3) 2"472 (5) 0 ( 2 ) " "  N(2) 2.999 (5) 0 (3" ) . .  "N(2) 3-123 (3) O(2 ' " ) "  .N(1) 2.911 (3) UI2 U13 U23 -0"0069 (6) -0"0136 (5) -0"0043 (9) 0"0025 (6) -0"0127 (7) -0"0017 (9) -0"0022 (3) -0"0129 (3) -0"0030 (4) -0"0016 (3) -0"0093 (5) 0"0013 (4) -0.0006 (3) -0.0096 (3) 0.0035 (4) -0.0022 (6) 0"0007 (5) -0.0022 (4) 0"0025 (6) 0"0009 (5) -0-0004 (4) Urea (C), (e), (f)  1.352 (2) 1.260 (3) 1.003 (4) 0.998 (5) Table 5. Bond angles (o) Urea-oxalic acid (a), (d), (g) C(2')-C(2)-O(2) 121.8 (2) C(2')-C(2)-O(3) 112.3 (3) O(2)-C(2)-O(3) 125.9 (2) C(2)-O(3)-H(1) 110 (3) O(1)-C(1)-N(1) 119.8 (3) O(1)-C(1)-N(2) 122.2 (2) N(1)-C(1)-N(2) 118.1 (3) C(1)-N(1)-H(5) 118 (3) C(1 ) -N(2)-H(2) 118 (2) C(1)-N(1)-H(4) 122 (3) C(1)-N(E)-H(3) 123 (2) H(4)-N(1)-H(5) 120 (3) H(2)-N(2)-H(3) 118 (4) (a) Present work. (b) Sabine, Cox & Craven (1969). Oxalic acid dihydrate (b), (e), (g) 121-0 (3) 112.4 (3) 126.6 (3) 114-4 (6) O(1')-" "N(1) 2"941 (4) (a) Present work. (b) Sabine, Cox & Craven (1969). (c) Pryor & Sanger (1970). (d) X-ray. (e) Neutron. (f)  Bond lengths corrected for thermal motion. (g) Bond lengths not corrected for thermal motion. KUTZELNIGG, W. • MECKE, R. (1961). Chem. Ber. 94, 1706. LARSON, A. C. (1970). Crystallographic Computing, pp. 291-294. Copenhagen: Munksgaard.  LONSDALE, K. (1941). Proc. Roy. Soc. A177, 272. PRYOR, g .  W. 8/; SANGER, P. L. (1970). Acta Cryst. A26, 543. SABINE, T. M., Cox, G. W. & CRAVEN, B. M. (1969). Acta Cryst. B25, 2437. (c) Pryor & Sanger (1970). (d) X-ray. (e) Neutron. (f)  Bond lengths corrected for thermal motion. (g) Bond lengths not corrected for thermal motion. Urea (c), (e), ( f)  121"7 (1) 121.7 (1) 116-6 (1) 119.0 (3) 120.2 (3) SCHUCH, A. F., MERRITT, L. L. & STURDIVANT, J. H. (1950). Amer. Crystallogr. Assoc., Abstracts of Meeting, April 10-12, p. 21. (see also Structure Reports 13, 477.) SELMAN, W. F. 8¢ HARKEMA, S. (1971). Prog. Report, Chem. Phys. Lab., Twente Univ. of Technology. STEWART, W. E. ~¢ SIDDALL, T. n .  (1970). Chem. Rev. 70, 517. WORSHAM, J. E. t~ BUSING, W. R. (1969). Acta Cryst. B25, 572. ZACHARIASEN, W. H. (1963). Acta Cryst. 16, 1139. Acta Cryst. (1972). B28, 1648 Structural studies of metal dithiocarbamates.V. The crystal and molecular structure of bis-(N, N-diethyldithio- carbamato)tellurium(II) By C. FABIANI, R. SPAGNA, A. VACIAGO and L. ZAMBONELLI, Laboratorio diStrutturistica Chimica 'Giordano Giacomello', CNR, Cittd Universitaria, 00100 Roma, Italy (Received 9 November 1971) A correction to a reference in Acta Cryst. (1971) B27, 1499 is given. In a paper of the above title (Fabiani, Spagna, Vaciago & L . P .  (1969). Nature, Lond. 221, 550 should read LAWTON' Zambonelli, 1971) the reference to the structure of lead(II) S . L .  & KOKOTAILO, (3. T. (1969). Nature, Lond. 221, 550. bis-(O,O-diisopropylphosphorodithioate) is incorrect. On page 1504, column 1, line 20 (Guzy, Raynor  & Stodulski, Reference 1969) should read (Lawton & Kokotailo, 1969) and in the FABIANI, C., SPAGNA, R., VACIAGO, A. ¢~ ZAMBONELLI, L. list of references GuzY, C. M., RAYNOR, J. B. & STODULSKI, (1971). Acta Cryst. B27, 1499. 

The crystal structure of urea oxalic acid (2:1)

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