Polyhedron Vol. 12, No. 10, pp. 1157-I 162, 1993 Printed in Great Britain

0277-5387/93 $6.00+.00 Pergamon Press Ltd

THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION-XXXI. COUNTER-ION EFFECTS

ON CRYSTALLIZATION PATHWAY OF RACEMATE SOLUTIONS-IV. THE CRYSTAL AND MOLECULAR

STRUCTURE OF RACEMIC (H30+)[Co(en),ox]C1, - Hz0 (I)

IVAN BERNAL,” JIWEN CAIt and JOZEF MYRCZEKt$

Chemistry Department, University of Houston, Houston, TX 77024-5641, U.S.A.

(Received 10 November 1992 ; accepted 27 January 1993)

Absbact-(H30+)[Co(en)20x]Cl~ * H20 (I), CoC1206N4C6H2,, crystallizes as a racemate in the monoclinic space group P2,/c (No. 14). Infinitely hydrogen-bonded spiral strings of homochiral [Co(en),ox]’ cations are formed which are wrapped about the two-fold screw axis of the crystals. Adjacent spirals are held together by hydrogen bonds between the waters and chlorides and the -NH2 hydrogens of the cations. Such an arrangement is also present in the conglomerate crystals of the [Co(en),ox]C1*4H20 (II) and [Co(en),ox] Br * Hz0 (III) derivatives ; however, unlike II and III, which crystallize as conglomerates and all spiral strings are of the same helicity, in I adjacent spirals are of opposite helical chirality and related to one another by the inversion operation of the space group.

It has been known for some timelm that the series [M(en),ox]X (M = Co, Cr, Rh ; X = Cl-, Br-) crystallize as conglomerates, whereas [Co(en),ox]I crystallizes both as a conglomerate and as a ra- cemate. ‘(‘I In fact, this observation was used by Shimura et al. w as evidence of the success of the thermodynamic formulation of the condition S, > 1.414& (where S, is the solubility of the racemate and S, that of the enantiomer), which defines what crystallization pathway will a given substance prefer-racemate or conglomerate. Rele- vant crystallization data on these systems are

*Author to whom correspondence should be addressed. t Fellow of the Robert A. Welch Foundation. $ On leave from the Technical University of Wroclaw,

l-5, Wroclaw, Poland. $These substances were identified as forming con-

glomerates either from solubility measurements, by seed- ing experiments or by measuring the CD spectra of result- ing crystalline material. No structural data were reported. See refs l(a), I(c) and 5 for details of the crystallization, seeding and spectroscopic experiments performed on these compounds.

summarized below :

Space Compound group Ref.

[Co(en)*ox]Cl - 4&o (III) P2,2,2, l(c), 2 [Co(en),ox]Br * HZ0 (IV) P2,2,2, 2, 3

[Wen)2oxlI 07 3 UC) [Cr(en)zox]Br 3 l(a), 4 [Rh(en),ox]Br 3 4 [Rh(en),o~]Cl.H~O 3 4

Our crystallization and structural studies of III’ and IV’ demonstrated that, in both compounds, homochiral cations are present in spiral strings linked by hydrogen bonds spanning from the ter- minal oxalato oxygens of one cation to the basal plane amines of an adjacent one, each string being an infinite polymer running along the length of the b-direction of the crystal.’ Adjacent strings are also homochiral with respect to their helical sense and in III and IV are held together by halide anions which are bonded to hydrogens of an axial -NH2 and to a water of crystallization, the latter being bonded to an axial -NH2 hydrogen of a cation belonging to the adjacent string. This stitching to-

1157

1158 I. BERNAL et al.

gether of the strings occurs across the entire length of adjacent spirals.

At the time we published ref. 2 we suggested that anything that interfered with the orderly formation of the spiral string and/or of the stitching pattern found in III and IV would probably result in the formation of heterochiral crystals (racemates). Sometime later we were able to prepare NH4

[Cr(en),ox]Cl,*H,O (VI)

1

and found that the ammonium cation hydrog n bonds to the terminal oxalato oxygens and, thusb disrupts the formation of the spiral strings menti

cb

ned above. It is, there- fore, noteworthy that VI rystallizes as a racemate in the space group P2l/c, s suggested earlier.2 We have been unable to pre

i

re the cobalt analogue to VI, despite repeated e rts, as discussed in our report’ on the crystallizati n behaviour of VI. The similarity of I and VI sugg B sted they should crystal- lize similarly and made it] possible to, once more, test our hypothesis’ sin e it was reasonable to expect that, as in VI, the also alter drastically 4,

ydronium cation would the hydrogen bond pattern

observed in III and IV. Finally, I was prepared y accident while attempt-

ing to grow crystals of [ o(en)20x]PbaCl~*2H20, the analogue of [Co(N-

f

e-ethylenediamine),ox] Pb2ClS * 2H,O-a camp und previously studied here.6 That effort was uns ccessful, but the product obtained easily compen ated for our failure to produce the lead compound we were seeking.

EXPERIMENTAL

Synthesis

Compound I was prepared as follows : PbCl, was slurried with distilled water, at 60°C and con- centrated HCl was added until all the solid had dissolved. A solution of [Co(en)20x]Cl * 4H202*‘,* in water was stirred at 60°C with enough of the acidi- fied lead chloride so that the Co : Pb ratio was 1: 2. The solution was allowed to cool, filtered and set aside to crystallize (ca 18C). Approximately equi- lateral crystals of the reddish-orange substance were formed, filtered and washed with ethanol. One was selected for single-crystal X-ray data collection.

Elemental analysis.’ For (H,0+)[Co(en)20x] Cl2 * H20, CoC1206N&H2, : Mol. wt = 375.10. Found: C, 19.4; H, 5.6; N, 16.1. Calc.: C, 19.2; H, 5.6; N, 14.9%.

X-ray d#raction

Data for I were collected with an Enraf-Nonius CAD-4 diffractometer operating with a Molecular Structure Corporation TEXRAY-230 modi- fication” of the SDP-Plus software package (see Table 1). ’ ’ The crystal was centred with data in the 22” < 20 d 34” range and examination of the cell constants and Niggli matrix” clearly showed it to crystallize in a primitive, monoclinic lattice whose

Table 1. S~ummary of data collection and processing parameters for racemic (H,O+)[Co(en)zox]C1z*H,O

Space group Cell constants a <A) b (A) c (A) B (“>

lc ; z = 4 mol cell- ‘) (g cn- ‘)

Scan width

Weights used

pw 7.397(2) 12.137(3) 17.01 l(3) 100.66(4) 1400.97 CoC120sN4CsH2, 375.10 1.660 MO-K, (A = 0.71073 A) 15.237 0.9247-0.999s 4” < 20 < 60” A6’ = 1.00+0.35 tan 0 3139 2543 0.0449 0.0458 w = [a(F z

Conglomerate crystallization-XXX111

Laue symmetry and systematic absences belong to those of the space group P2,/c (No. 14). The inten- sity data set was corrected for absorption using empirical curves derived from Psi scans “,’ ’ of five reflections. The scattering curves were taken from Cromer and Waber’s compilation. ’ 3

RESULTS

The contents of the asymmetric unit are shown in Fig. 1, which shows that there is a cobalt cation, a hydronium cation and a water of crystallization which is hydrogen bonded to a terminal oxalato oxygen [O(3)] and to the chloride anion [C1(2)], which in turn is hydrogen bonded to a terminal -NH2 hydrogen (Hl). The hydronium cation is weakly hydrogen bonded to O(4), but it also blocks access to a non-bonded pair of O(4). Finally, Cl(l) is hydrogen bonded to H(8) and H(9), thus blocking some of the hydrogens needed by the terminal oxal- ato oxygens to form the helical strings observed in the conglomerate crystallization of III and IV.

Figure 2 is a packing diagram in which the centre of the cell is one of the inversion centres, as readily ascertained by the relationship of the chloride and waters of crystallization clustered about that point. Note also that there are strings of cations running

Hl4

Hw4

Fig. 1. A view of the contents of the asymmetric unit. Note the position of the (H,O+) cation, blocking access to O(4) and of the water of crystallization blocking access to O(3) of the oxalato ligand. Also note the position of the chloride anions, which effectively block access to the -NH, hydrogens. These hydrogen-bonded interactions effectively eliminate all chances of forming the spiral strings of cobalt cations found (see refs 2 and 5) in the series of [Co(en),ox]X (X = Cl, Br, I) and whose for- mation was postulated as the origin of conglomerate

crystallization.

A

Fig. 2. A view of the unit cell contents. Here, the viewer can see the approach between cobalt cations blocked by the water, the (H,O+) cation and the chlorides. Note the inversion eentre located at the eentre of the cell. This centre relates enantiomorphic pairs of cations as well as

spiral strings of opposite helicity.

along the b-axis, as expected from the space group ; however, given the position of the inversion centre, the cations of adjacent strings are of opposite chirality, as is the sense of the helical chirality of adjacent spiral strings. Thus, not only does the lattice contain racemic pairs of [Co(en),ox]+ cations, but an enantiomorphic relationship exists also between the helicities of the entire sets of adjacent strings.

Table 2(D) shows that the shortest hydrogen bond in the entire lattice is between O(4) and Hw(3) and the next shortest is between O(3) and Hw(2). Therefore, the two terminal oxalato oxygens are engaged in hydrogen bonding which preclude the formation of the spiral strings observed in the case of the chloride (III) and the bromide (IV). Such was precisely the case with the double salt NH4[Cr (en)zox]C12 * H,O (VI),5 with which compound I is nearly isomorphous. Given that fact, we refer the interested reader to the original paper on VI’ for details of the hydrogen bonding present there.

Finally, the hydronium cation is very far from the water of crystallization (nearest contact, see Table 2(D), is 2.21 A). Therefore, the correct formulation of this hydrated cation is H30+ and not HSOz+.

DISCUSSION

It was our good fortune to accidentally obtain I since it is chemically different, yet nearly iso-

co--o(l) 1.915(l) co-O(2) 1.920(l) Co-N( 1) 1.941(l) CO-N(~) 1.941(l) Co-N(3) 1.925(l) CO-N(~) 1.955(l)

O( l)-Go-O(2) 0( 1 )--co-N(l) 0( 1 )-CO-N(~) 0( lj-co-N(3) 0(1)-G--N(4) 0(2jCo-N( 1) 0(2)-&-N(2) 0(2jCo-N(3) 0(2jCo-N(4) N(ljCo-N(2) N( l j-co-N(3)

85.8(4)1 91.8(5] 90.5(5)1

173.3(51 90.3(51 89.4(5]

173.9(5] 88.6(5) 92.6(5) 85.9(5) 92.0(6)

0(2)--co--o( 1 )--c(5) N( 1 )--co-0(1)-C(5)

N(2jCo--0(l)--C(5) N(3)-Co--0(l)--C(5) N(4)-&-0( ljC(5) O(ljCo-0(2)-C(6) N(ljCo-O(2)-C(6)

N(2)--Co--O(2)--C(6) N(3)-Co-0(2)-C(6) N(4jCo-0(2)-C(6) 0( l)-Co-N( 1 )-C( 1) 0(2)-X0-N( 1 jC( 1) N(2)-Co-N( 1 jC( 1) N(3)---Co-N(ljC(1) N(4jCo-N( 1 jC( 1)

0( 1 )--Co--N(2>--C(2) 0(2)-X0-N(2jC(2) N(ljCo-N(2jC(2) N(3jCo-N(2)-C(2) N(4)-Co-N(2)-C(2) O(ljCo-N(3jC(3) O(2)--Co-N(3)-C(3)

Cl( 1)-H(2) 2.38 Cl(ljH(10) 2.39

Cl(2jHQ) 2.32 O(3)-Hw( 1) 2.48

0(3jHw(2) 1.66

0(4jHw(3) 1.59 Cl(l)-H(16) 2.39 Cl( I)-Hw(4) 2.03

Cl(2jH(8) 2.48 C](2)-H(9) 2.31

0(4)--H(7) 2.10

O(4jW 15) 2.42 Ow(ljH+ 2.21

Table 2. Bond distances (A) and angles (“) for I

(A) Distances

0(1)-C(5) 1.284(2) N(3)-C(3) 1.466(2) 0(2jC(6) 1.276(2) N(4)--C(4) 1.480(2) 0(3)-C(5) 1.232(2) C(l)-C(2) 1.506(2) 0(4jC(6) 1.239(2) C(3)--C(4) 1.48.5(3) N(ljC(l) 1.485(2) C(5)--c(6) 1.531(2) N(2jC(2) 1.478(2)

(B) Angles N( 1)--G-N(4) 177.2(5) N(2jC(2jC(l) 107.1(2) N(2jCo-N(3) 95.3(5) N(3jC(3jC(4) 107.2(2)

N(2>--co--N(4) 92.3(S) N(4jC(4)--C(3) 108.2(2) N(3)-Co-N(4) 86.1(6) O(l)-C(5jO(3) 125.7(2) co-O( 1)-C(5) 112.3(l) O(ljC(5jC(6) 114.4(l) Co--o(2)--c(6) 111.8(l) 0(3t-c(5)--c(6) 119.9(l) Co-N( 1)-C( 1) 110.5(9) O(2)-C(6)--0(4) 125.0(2) Co-N(2)-C(2) 108.2(9) 0(2jC(6)-C(5) 115.4(l) Co-N(3jC(3) 108.8(l) 0(4jC(6)--C(S) 119.6(l)

Co--N(4)--c(4) 109.1(l)

N(ljWjC(2) 106.1(l)

(C) Torsional angles 2.2 N( 1 j-co-N(3jC(3) - 162.0

91.5 N(2)-Co-N(3jC(3) 111.9 177.4 N(4jCo-N(3)-C(3) 20.0

- 32.8 0( 1 j-Co-N(4jC(4) - 178.5 -90.3 O(2)-Co-N(4)-C(4) 95.6

0.6 N( I)-Co-N(4jC(4) - 38.4 -91.2 N(2)-Co-N(4jC(4) -88.1 -52.1 N(3jCo-N(4)-C(4) 7.1 176.8 c0--0(1jC(5)-0(3) 174.4 90.8 Co-O(IjC(5 j-c(6) -4.2 99.5 Co-O(2)-C(6jO(4) 176.7

- 174.7 Co-O(2)-C(6)-C(5) -2.9 9.2 Co-N(l)-C(l)-C(2) - 34.6

-86.1 Co-N(2)-C(2)-C(1) -43.1 -40.6 Co-N(3 jC(3jC(4) -42.7 -72.6 Co-N(4 jC(4jC(3) - 32.4 -20.1 N(l)--C(lt-C(2)-N(2) 50.3

19.2 N(3)-C(3)-C(4 jN(4) 48.9 110.8 OUjC(5jC(6)--0(2) 5.0

- 162.9 O(l)--C(5jC(6jO(4) - 174.7 -37.7 O(3)-C(5)-C(6)-0(2) - 173.7 -72.7 0(3)--C(5)-C(6)--0(4) 6.6

(D) Selected list of hydrogen bonds N(l)-H(2) . . . Cl( 1) 162.4 N(3 jH(10). . . Cl(l) 153.2 N(1 jH(l)...C1(2) 170.7 Ow(ljHw(1) . . O(3) 86.1 Ow( l)-Hw(2) . . . O(3) 149.4 Ow(2)-Hw(3). . O(4) 151.9 N(4)-H( 16) . . . Cl( 1) 177.1 N(4) at x+1, y, z Ow(2)-Hw(4). . . Cl(l) 152.5 Ow(2) at 1 -x, -y, z N(2jH(8). . . Cl(2) 158.4 N(2) at I-x, y-1/2, 1/2-z N(3jH(9). . . Cl(2) 178.1 N(3)at 1-x,y-l/2, 1/2-z N(2jH(7). . . O(4) 162.6 N(2) at -x, y-1/2, 1/2-z N(4jH( 15) . . . O(4) 150.1 N(4) at -x, y--1/2, 1/2-z Ow(2)-H + . . . Ow(1) 85.5 Ow(2)atx-l,y,z

No e.s.d.s are shown sin hydrogen atoms were not refined. Numbers in parentheses estimated standard deviations in the least significant digits.

Conglomerate crystallization-XXX111 1161

morphous with the ammonium salt VI5 and pro- provided by the National Science Foundation, whom we

vided us with an additional piece of the puzzle men- also thank.

tioned in the Introduction ; namely, the ammonium cation of VI was bound to form hydrogen bonds REFERENCES

with the oxalato oxygens, with the anions and with the water of crystallization. Therefore, it would be

1. (a) Alfred Werner was the first to establish a large

expected to alter the nature of the packing by (a) solubility difference between the racemate and the enantiomers of the cobalt and chromium

intercalating between cobalt cations and modifying compounds, see A. Werner, Chem. Ber. 1914, 47, or destroying the spiral strings, or by (b) upsetting 2171; (b) further work in this area was done by K. the nature of the bridges between adjacent strings, Yamasaki, H. Igarishi and Y. Yoshikawa, Inorg. or both. The same comments would apply to the Nucl. Chem. Lett. 1968, 4, 491 ; (c) for a more hydrogen bonding scheme expected for I if our pre- quantitative description of the phase diagram of this

vious statements5 were correct and general. substance see K. Yamanari, J. Hidaka and Y.

Figure 1, together with the hydrogen bonding Shimura, Bull. Chem. Sot. Japan 1973, 46, 3724;

data in Table 2(D), shows that Cl(l)- and Cl(2)) (d) for the crystal structure of [Co(en),ox]Br - H20,

are busily enagaged in hydrogen bonds with both determined from crystals of pre-resolved material,

axial and equatorial -NH2 hydrogens and that see ref. 3. However, that structural study (ref. 3)

irrespective of the strength or weakness of their was carried out with a very limited set of film data;

hydrogen bonds,. they present a steric barrier to the consequently, it lacks precision and no hydrogen

approach of a second cobalt cation. Consequently, atom positions were given for either the cation or the water of crystallization.

the onset of the formation of a spiral string is 2. Using crystals from conglomerate crystallization obviously hopelessly compromised. Second, on the experiments we have determined the crystals struc-

other side of the cobalt cation, terminal oxygens tures of [Co(en)20x]Br*HZ0 and [Co(en),ox]

[O(3) and O(4)] are hydrogen bonded to the hydron- Cl-4H20. In general, the former agrees with the

ium cation and to the water of crystallization, results given in ref. 3 ; the latter is a new structural

Ow(1). Consequently, the presence of such hydro- analysis. A detailed description and comparison of

gen bonds would force additional hydrogen bonds both will be published elsewhere: I. Bernal, J.

between oxalato terminal oxygens and -NH2 Cetrullo, J. Myrczek and S. S. Massoud, J. Coord.

hydrogens to be bifurcated bonds insofar as the Chem., submitted. Both compounds crystallize in the

oxygens are concerned. Such bonds would be enantiomorphic space group P2,2,2 ,, with z = 4.

3. T. Aoki, K. Matsumoto, S. Ooi and H. Kuroya, Bull. expected to be weaker, if they took place. Moreover, Chem. Sot. Japan 1973,46, 159. the chlorides, waters and hydronium cations are 4. R. D. Gillard and L. H. R. Tipping, J. Chem. Sot., sterically demanding fragments which would effec- Dalton Trans. 1977, 1241. tively hinder access by another cobalt cation to the 5. I. Bernal, J. Myrczek and J. Cai, J. Coord. Chem., in

amino hydrogens. Again, the possibility of retaining press.

the spiral string geometry observed in previous 6. J. Cai, J. Myrczek and I. Bernal, J. Chem. Sot.,

cases is seriously impaired on the both sides of Chem. Commun. 1992,1147.

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These observations strengthen our previously McGraw-Hill, New York (1949).

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of the [Co(trien),(NO,),]+, [Co(en)l(NOZ)Z]+ and Vol. XVII, p. 96. McGraw-Hill, New York (1978).

9. [Co(en),ox]+ cations undergo conglomerate crystal-

Galbraith Laboratories, Inc., P.O. Box 51610, Knox- ville, TN 37950-1610.

lization.2*‘“17 Therefore, there appears to be con- 10. TEXRAY-230 is a modification of the SDP-Plus’ * sistency in our crystallization mechanistic con- set of X-ray crystallographic programs distributed clusions, even when we compare members of by Molecular Structure Corporation, 3200 Research

different series of cations-a fact which is greatly Forest Dr, The Woodlands, TX 77386, for use with

satisfying. their automation of the CAD-4 diffractometer.

Supplementary material available. Compound 1: 11 SDP-Plus is the Enraf-Nonius Corporation X-ray

anisotropic thermal parameters (1 page), structure diffraction data processing programs distributed by

factor table (28 pages). B. A. Frenz & Associates, 209 University Dr. East, College Station, TX 77840.

12. R. B. Roof, A Theoretical Extension of the Reduced Cell Concept in Crystallography, Report LA-4038,

Acknowledgements-We thank the Robert A. Welch Los Alamos Scientific Laboratory (1969). Foundation for a grant (E-594; to IB) and for a fellow- 13. D. T. Cromer and J. T. Waber, International Tables ship to J. Cai and J. Myrczek. The structural work was for X-Ray Crystallography, Vol. IV, Tables 2.2.8 and carried out with diffractometer purchased with funds 2.3.1, respectively, for the scattering factor curves

1162 I. BERNAL et al.

and the anomalous dispersion values. Kynoch Press, 16. I. Bernal and J. Cetrullo, Inorg. Chim. Acta 1988, Birmingham (1975). 150, 75.

14. I. Bernal, Inorg. Chim. Acta 1985,96,99. 17. I. Bernal, S. Berhane and J. Cetrullo, Strut. Chem. 15. I. Bernal and J. Cetrullo, Inorg. Chim. Acta 1988, 1990,1, 361.

144.227.