Aust. J. Chem., 1975,28,2129-35
Crystal and Molecular Structure of
(RS,RS)-Tetraammine(4,5-dihydroxy-4,5-dimethyl1-pyrroline-2-carboxylato)cobalt(~~~)
Perchlorate
Glen B. RobertsonA and Peter 0. whirnpAsB
A Research School of Chemistry, Australian National University,
P.O. Box 4, Canberra, A.C.T. 2600.
TO whom correspondence should be addressed.
Abstract
The structure of a cobalt(n1) tetraammine complex of 4,5-dihydroxy-4,5-dimethyl-I-pyrroline-2carboxylic acid (abbreviated as hmpc), (RS,RS)-[CO(NH~)~(~~~C)]
(C104),,H20, has been determined from three-dimensional X-ray data collected by counter methods. Crystals are monoclinic,
space group P2,/c, with a 11.984(5), b 8.836(4), c 19.609(7) A, P 110.58(2)", Z 4. The structure
has been refined to weighted and unweighted R-factors of 0.068 and 0.063, respectively, for the
1616 independent reflections with Z/a(Z) > 3.0. Hydrogen atoms could not be located and have
not been included in the scattering model. There is considerable steric strain within the
substituted pyrroline ligand, and the C=N distance is lS293(8)A. Surprisingly, the methyl groups
in the 4- and 5-positions are in a cisoid configuration (the torsion angle for the methyl groups
about the 4-5 bond is 39.5"), and consequently the hydroxyl oxygen atoms are close [O-0 distance,
2.583(8) A]; this suggests that there may be a bridging hydrogen atom.
Introduction
The reaction of the tetraammine(2-iminopropanoato)cobalt(~~~)
ion (1) with
biacetyl to give the cobalt(111)tetraammine complex (2) of 4,5-dihydroxy-4,5-dimethylI-pyrroline-2-carboxylic acid has been described.' Although the structure of the
complex cation was described briefly in that paper, we now report complete details
of the three-dimensional X-ray structural analysis of the cobalt(111) complex
[Co(NH&(hm~c)l (ClO4)2&O.
Experimental
Crystals of the cobalt(111) complex of 4,5-dihydroxy-4,5-dimethyl-l-pyrroline-2-carboxylic
acid
(hrnpc), [C~(NH~)~(hrnpc)]
(ClO,),,H,O, were supplied by Dr A. M. Sargeson and Dr J. MacB.
Harrowfield of this School.
Harrowfield, J. MacB., Robertson, G . B., Sargeson, A. M., and Whimp, P. O., J. Chem. Soc.,
Chem. Commun., 1975, 109.
G. B. Robertson and P. 0. Whimp
Crystal Data
[Co(NH,),(hmpc)] (C104),,HzO; C,HZ4Cl2CoN5Ol3; M 516.13; monoclinic; a 11.984(5);
b 8.836(4); c l9.609(7) A; P 110.58(2)"; U 1943.9 A3; D m 1.75(1), by flotation; Z 4; D, 1.76 g
~ m - F(000),
~ ;
1064; space group P21/c (C:,, No. 14); Cu Ka radiation; A, 1.5418 A; p, 99.84
cm-l.
Crystal Alignment and Data Collection
Crystals were mounted on quartz fibres with Araldite, and preliminary Weissenberg and
precession photographs were taken to establish crystal quality, space group and approximate cell
dimensions. The crystal chosen for data collection was transferred to a Picker FACS-I fully
automatic four-circle diffractometer, and was aligned with the crystallographic b-axis and the
instrumental @-axis approximately coincidental. Cell dimensions and crystal orientation matrix,
together with their estimated standard errors, were derived in the usual wayZ from the leastsquares refinement of the 28, o,x, and @ values obtained for 12 carefully centred high angle
reflections (28 88").
Graphite-crystal monochromated Cu Ka radiation was used to collect 3776 reflections, including
'standards' (see below), within the range 3" < 28 $ 125". Details of the method of data collection,
together with formulae used in the reduction of intensity data to values of lF,l, have been described
previ~usly.~
The experimental parameters used in this structural analysis were: tube take-off angle,
3 .OO; crystal-counter distance, 28.5 cm; 28 velocity, 2"/min; 28 scan range, 1. l o below the
Cu Kal peak to 1.1" above the Cu KaZ peak; background counting time, 10 s (each side); instrumental 'uncertainty factor' ( p Z ) , 0.002. The intensities of three standard reflections [indices
{O,Z,ll), {0,6,0), {6,O,iZ}]were monitored after each 100 measurements. Each standard reflection
showed a regular time-dependent loss of intensity of c. 18 % during data collection. Decomposition
was assumed to be isotropic and 28-independent, and the intensity data were corrected accordingly.
The data were sorted, equivalent reflection forms were averaged, and those reflections for which
I/a(Z) < 3.0 were discarded as being unobserved. The statistical R-factor for the 1616 independent
reflections of the terminal data set was 0.041.
Solution and Refinement of the Stvuctuve
A three-dimensional Patterson map showed the positions of the cobalt atom and the six atoms
of the first coordination sphere. The remaining atoms were located, in stereochemically reasonable
positions, from successive Fourier difference maps. When data were used which had been
corrected for absorption effects,* block-diagonal least-squares refinement of the overall scale factor,
atomic positional parameters, and anisotropic thermal parameters of the form
for all non-hydrogen atoms, converged with R = 0.063 and R, = 0.068.1 It was not possible to
locate any hydrogen atoms on the final electron-density difference map, and consequently hydrogen
atom contributions have not been included in the scattering model. One perchlorate anion [based
on Cl(l)] is disordered, and it was possible to locate and refine eight oxygen atoms about Cl(1).
As these oxygen atoms were of approximately equal electron-density, populations of 0.5 were
assumed, and no attempt was made to refine these population parameters.
On the final cycle of least-squares refinement, no individual parameter shift was greater than
0.1 e.s.d. (estimated standard deviations derive from inversion of the block-diagonal matrices).
* The crystal used for data collection was bounded by the faces {loo), {TOO), {lOZ}, {i02}, {010}
and {OiO}. Crystal dimensions were: {loo) to {TOO}, 0.0125cm; {I021 to {lOZ}, 0.02cm;
{010} to {OTO), 0.025 cm. Transmission factors (applied to IF,/)ranged from 0.359 to 0-614.
1R = ZIIF,I - IF,II/CIF,I and R, = {Zw[lF,I- IFc1]2/C~IFo/2}112,
where F, is the observed, and
F, is the calculated structure factor, and w[= l/oZ(Fo)]is the weight. The function minimized
during least-squares refinement is Zw(lF,I - lF,I)2.
The programs contained in the Picker Corporation FACS-I Disk Operating System (1972) were
used for all phases of diffractometer control and data collection.
Robertson, G. B., and Whimp, P. O., Aust. J. Chem., 1975, 28, 729.
There were no unusual features on the final electron-density difference map, and the highest
residual peak was 0.6 e/A3. The standard deviation of an observation of unit weight, defined as
[Z(lFol- lFc1)2/(m-n)]1'2 [where m is the number of observations and n(= 289) is the number of
parameters varied] is 2.01.
Scattering factors for all atoms were taken from ref.4 and those for Co and C1 were corrected for
the real and imaginary parts of anomalous s ~ a t t e r i n g . ~ . ~
Final atomic positional parameters, together with their estimated standard deviations, are listed
in Table 1. A listing of thermal parameters, and of observed and calculated structure factor
amplitudes ( x 10, electrons), is available.*
Table 1. Atomic positional parameters
Estimated standard deviations (in parentheses) in all tables and the text refer to the least
significant digits
Atom
x/a
CO
O(1)
O(2)
Of411
O(51)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)
C(4)
C(5)
C(41)
0.30178(11)
0.4447(4)
0.5327(4)
0.2481(6)
0.0975(5)
0,2531(5)
0.2398(6)
0.3765(6)
0.3689(6)
0.1548(6)
0,4481(7)
0,3331(6)
0.3036(7)
0,1979(8)
0.1451(7)
0.1118(9)
~ l b
0.17887(15)
0,1757(6)
0,0540(6)
- 0.3080(7)
- 0.11 87(7)
0.0244(7)
0.3394(7)
0.3362(9)
0.0192(8)
0.1785(9)
0.0785(8)
- O~OlOO(8)
- 0.1359(8)
- 0~2106(10)
-0.0726(9)
-0.3003fll)
z/c
Atom
x/a
Y/b
0.11086(6)
0,1943(2)
0.2995(3)
0.1638(3)
0~0800(3)
0.1644(3)
0.1574(3)
0,0702(3)
0.0663(3)
0.0236(3)
0.2431(4)
0.2264(4)
0.2676(4)
0.2048(4)
0,1533(4)
0.2280(6)
C(51)
Cl(1)
O(11)
O(12)
O(13)
O(14)
O(15)
O(16)
O(17)
O(18)
Cl(2)
O(21)
O(22)
O(23)
O(24)
Solv.
0,0519(8)
0.8636(2)
0.9816(12)
0.8542(17)
0.8206(14)
0.7880(21)
0.8334(23)
0.9557(19)
0.7784(23)
0.8486(22)
0.3172(2)
0.2400(8)
0.3979(10)
0.2635(8)
0.3777(7)
0.5932(9)
0.0160(10)
0.3853(3)
0.3487(20)
0,4571(19)
0.2322(15)
0.4644(27)
0,3657(40)
0.3920(24)
0.3308(32)
0,5448(24)
0.3124(3)
0.2302(10)
0.2093(15)
0.3774(11)
0.4126(10)
0.3091(11)
z/c
0.1721(5)
0,0539(1)
0.0679(10)
-0.0116(8)
0.0372(7)
0.0766(11)
0.1130(14)
0.1133(11)
0.0014(14)
0.0468(12)
0.3622(1)
0.3058(3)
0.4075(6)
0.4067(4)
0.3335(4)
0.5591(5)
Computer Programs
The data reduction SETUP^), sorting (SORTIE),
Fourier (ANUFOR),
and block-diagonal least-squares
refinement (BLKLSQ)
programs have been described previou~ly.~,~
Absorption corrections were carried
out using TOMPAB,
a locally modified version (J. D. Bell) of the Brookhaven National Laboratory
absorption correction p r ~ g r a m . ~Figures were produced by means of ORTEP," while geometry
calculations were carried out through ORFFE." All calculations were done on the Univac-1108
computer of the Australian National University Computer Centre.
Results and Discussion
Crystals contain [Co(N~,),(hmpc)]~+cations, together with perchlorate anions;
there is one molecule of water of crystallization per asymmetric unit. Neither the
complex cation nor the perchlorate anions have symmetry (crystallographic or virtual)
* Copies are available on application to the Editor-in-Chief, Editorial and Publications Service,
CSIRO, 372 Albert Street, East Melbourne, Vic. 3002.
'International Tables for X-Ray Crystallography' Vol. 3, p. 202 (Kynoch Press: Birmingham 1962).
Prewitt, C. T., Ph.D. Thesis, Massachusetts Institute of Technology, 1962, p. 163.
Cromer, D. T., and Liberman, D., J. Chem. Phys., 1970, 53, 1891.
Robertson, G. B., and Whimp, P. O., Znorg. Chem., 1974, 13, 1047.
Robertson, 6.B., and Whimp, P. O., Znovg. Chem., 1974, 13, 2082.
For details of the analytical absorption method, see: De Meulenaer, J., and Tompa, H., Acta
Crystallogr., 1965, 19, 1014; Alcock, N. W., Acta Crystallogr., Sect. A, 1969, 25, 518.
l o Johnson, C. K., Report ORNL-3794, Oak Ridge National Laboratory, Oak Ridge, Tenn., 1965.
l1 Busing, W. R., Martin, K. O., and Levy, H. A., Report ORNL-TM-306, Oak Ridge National
Laboratory, Oak Ridge, Tenn., 1964.
G . B. Robertson and P. 0.Whimp
higher than C,. A perspective view of the complex cation, together with the atom
numbering scheme, is shown by the stereopairs of Fig. 1. The contents of one unit
cell are shown by the stereopairs of Fig. 2. In both figures, the thermal ellipsoids
Fig. 1. The overall stereochemistry of the complex cation showing the atom numbering
scheme. The configuration at the chiral centres C(4) and C(5) is S,S in this illustration.
Fig. 2. Contents of one unit cell ( s o ~ vis the oxygen atom of the molecule of water of
crystallization).
have been drawn to include 50% of the probability distribution. The atoms C(4)
and C(5) are chiral centres, and crystals contain equal numbers of (S,S)-[Co(~~,),(hmpc)]~
and
+ (R,R)-[Co(NH,),(hmp~)]~' cations.
Principal bond distances, together with their estimated standard deviations, are
listed in Table 2. Interbond angles are given in Table 3, and the results of leastsquares planes calculations are listed in Tables 4 and 5.
Table 2. Bond distances (A)
-
Atoms
CO-O(1)
CO-N(3)
O(l)-c(l)
W)-N(l)
c(4)-C(5)
~(5)-~(1)
Cl(1)-O(11)
Cl(1)-O(14)
Cl(1)-O(17)
Cl(2)-O(22)
Distance
Atoms
1 .909(4)
1 .968(8)
1 .276(9)
1 .293(8)
1 .568(11)
1.503(10)
1.381(15)
1 .338(27)
1 .264(23)
1 .397(12)
CO-N(1)
Co-N(4)
C(1)-0(2)
C(2)-C(3)
C(4)-O(41)
C(5)-O(5l)
Cl(1)-O(12)
Cl(1)-O(15)
Cl(1)-O(18)
Cl(2)-O(23)
---
Distance
1.933(7)
1 .973(8)
1 .228(7)
1.488(12)
1 446(12)
1 .407(9)
1 .400(16)
lS341(31)
1.422(21)
1 .379(11)
Atoms
CO-N(2)
c0-N(5)
C(l)-C(2)
C(3)-C(4)
C(4)-C(41)
C(5)-C(51)
Cl(1)-O(13)
Cl(1)-O(16)
Cl(2)-O(21)
Cl(2)-O(24)
-
Distance
1 .968(7)
1 .977(6)
19517(11)
1.568(10)
1 .494(15)
1 .512(13)
1 444(14)
1 .294(18)
1 .373(8)
1 .383(10)
.
Table 3. Interbond angles (degrees)
The perchlorate group centred on Cl(1) is disordered and, consequently, interbond angles about
Cl(1) have not been listed
Atoms
Angle
Atoms
Angle
Atoms
Angle
Table 4. Least-squares planes
The plane equations LX+ MY+ NZ+ D = 0 refer to orthogonal coordinates where
X = 11.9839x+O.Oy-6.8924~ Y = O.Ox+8.8364y+O.Oz Z = O.Ox+O.Oy+18.3572~
Plane
1
2
3
A
Atoms defining plane
Co, (XI), NU)
N(1h C(2), C(3)
N(1), C(2h C(5)
EquationA
0.5639X-0.7043Y-O.43122+0.3824
=0
0~6028X-O~6547Y-0~45612+0~3729
=0
0.5640X-O.6934Y-0.44842+0.4315
=0
Blow, D. M., Acta Cvystallogv., 1960, 13, 168.
The complex cation is essentially octahedral about the central cobalt(111) ion.
Two cis coordination sites are occupied by the nitrogen and the carboxyl oxygen
G. B. Robertson and P. 0. Whimp
atoms of the 4,5-dihydroxy-4,5-dimethyl-1-pyrroline-2-carboxylic
acid ligand; the
four remaining sites are occupied by coordinated ammonia groups.
Table 5. Deviations (A) from the least-squares planes
Atom
Plane 1
Atom
Plane 2
Atom
Plane 3
The Co-N(NH3) distances, which vary from 1.968(7) to 1.977(6) A, are equal
within experimental error (3.00), and average 1.972 A. This average value is, in
turn, in excellent agreement with the average value of 1.972A found for
[CO(NH~)~{HN=C(CH~)CH~C(CH~)(NH~)(CO~)}]
S20,,3 and also with the value of
1.978(10) A found for [Co(NH3),(N02)] Br2.12 The Co-N(imine) distance [Co-N(1),
1.933(7) A] is, likewise, in excellent agreement with the corresponding distance of
1.924(5) A observed for the cobalt(111) derivative of 2-amino-4-imino-2-methylpentanoic acid.3 In both of these derivatives, the Co-N(imine) distances are significantly
shorter (by c. 0.04A) than the Co-N(ammine) distances. This contraction
reflects the differing a-bond radius of nitrogen atoms in sp2 and sp3 hybridization
states.
The bond length Co-O(1) [1.909(4)A] is only marginally shorter than the
corresponding distance [1.914(4) A] found for [Co(NH3),{HN=C(CH3)CH2C(CH3)(NH2)(CO2))I2+catiom3 These values are in excellent agreement with those found
for the corresponding distances in a number of other cobalt(111)-amino acid
In common with
derivatives, e.g. 1.914(6) A for A-P,-(~,~)-[Co(trien)(Gly)]~+.~~
other amino acid and peptide derivatives,13,14 the coordinated carbonyl group is
polarized, and the C(1)-O(1) bond [1*276(9)A] is significantly longer than the
'free' C-0 bond [C(1)-0(2), 1.228(7) A] (Ala % 6). In the 2-amino-4-imino-2methylpentanoic acid cobalt(111) deri~ative,~
the corresponding values are 1.270(7)
and 1.233(6) A.
There is, clearly, considerable steric strain associated with fitting the 4,5-dihydroxy4,5-dimethyl-1-pyrroline-2-carboxylicacid ligand about the central cobalt(~u)ion.
Thus, the angle O(1)-Co-N(l) [82.8(2)"] is significantly strained from its expected
value of 90". There is also considerable steric strain within the pyrroline ring, and the
internal ring angles at N(l), C(2), C(3), C(4) and C(5), deviate significantly from their
expected values. In addition, the distances C(3)-C(4) and C(4)-C(5) [I .569(10) and
Cotton, F. A., and Edwards, W. T., Acta Crystallogu., Sect. B, 1968, 24, 474.
Buckingham, D. A., Cresswell, P. J., Dellaca, R. J., Dwyer, M., Gainsford, G. J., Marzilli, L. G . ,
Maxwell, I. E., Robinson, W. T., Sargeson, A. M., and Turnbull, K. R., J. Ameu. Chem. Soc.,
1974, 96, 1713.
l4 Freeman, H. C., Marzilli, L. G., and Maxwell, I. E., Znoug. Chem., 1970, 9, 2408.
l2
l3
1+569(11)A]are longer (although not significantly so) than the value normally
expected for simple C-C single bonds (1 .MA). A similar lengthening is also
observed for the C=N imine bond [N(l)-C(2), 1.293(8) tf] which is significantly
longer than the value of 1.252(7)A found for the corresponding distance in
[CO(NH,),(HN=C(CH,)CH~C(CH,)(NH~)(C~,))]~
. 3 The present C=N distance
is, however, similar to the C-N(amidine) distance of 1+31(2)A found for the
[Co(H2NCH2CH2NH2){H2NCH2CH2N=C(NH2)CH2NH2)Cl]+
cation,15 where the
C-N bond order is thought to be less than 2.
Perhaps the most surprising feature of the 4,5-dihydroxy-4,5-dimethyl-1-pyrroline2-carboxylic acid ligand is the cisoid arrangement of the two methyl groups about the
C(4)-C(5) bond. The torsion angle about this bond [defined as the dihedral angle
between the two three-atom planes {C(41), C(4), C(5)) and {C(4), C(5), C(51))I is 39.5".
Clearly, from steric considerations alone, the methyl groups would be expected to
adopt a trans conformation.
As noted above, it was not possible to locate any hydrogen atoms. Although all
but two of the hydrogen atoms are associated with ammonia groups and methyl
groups, it is surprising that those bonded to the hydroxyl oxygen atoms O(41) and
O(51) were not found on the final electron-density difference map. In particular,
the proximity of these oxygen atoms [0(41)-0(51), 2.583(8) A] suggests that there
could be intramolecular hydrogen-bonding, the 0-He . O angle being c. 130-140".
However, as either O(41) or O(51) could be the donor atom in such a hydrogenbonding scheme, it is possible that the two hydroxyl hydrogen atoms are
disordered and are shared equally between four possible positions. Clearly, such
'half' hydrogen atoms would be indistinguishable from random noise on the final
electron-density difference map.
+
Acknowledgments
We are grateful to Dr A. M. Sargeson and Dr J. MacB. Harrowfield for helpful
discussions. We thank the staff of the Australian National University Computer
Centre for generous allocations of time on the Univac-1108 computer.
Manuscript received 22 May 1975
l5
Buckingham, D. A,, Foxman, B. M., Sargeson, A. M., and Zanella, A., J. Amer. Chem.
1972,94, 1007.
Soc.,