Inorg. Phys. Theor. 415

The Crystal and Molecular Structure of Bis( histidino)nickel(ii) Mono- hydrate

By K. A. Fraser and Marjorie M. Harding, Department of Chemistry, University of Edinburgh

The structure of bis( histidino) nickel ( 1 1 ) monohydrate has been determined from three-dimensional X-ray dif- fraction data. The crystals are orthorhombic with a = 15.1 8, b = 13-05, c = 7.72 A. and space-group Aba2. Posi- tional and anisotropic thermal parameters have been refined by least-squares methods ; the final R factor is 0.082. The crystal contains molecules of bis- (D-histidino) nickel and bis-( L-histidino) nickel, related to each other by glide planes. The nickel atoms lie on two-fold axes and are octahedrally co-ordinated by the amino-nitrogen, the imidazole nitrogen, and a carboxyl oxygen of each histidine group, at 2.1 1, 2.09, 2.1 1 A, respectively (e.s.d. ca. 0.01 A).

THE structure of bis(histidino)nickel(II) monohydrate (I) has been determined as one of a series of structures of complexes of bivalent metal ions with amino-acids. Certain bivalent ions, in other respects chemically rather

L 1 2

similar to nickel, are frequently essential in enzyme- catalysed reactions, and often interaction of the metal ion with a histidine residue in the polypeptide chain of the enzyme is involved. Our general aim is to provide stereochemical information relevant to these inter- actions, but we shall also compare the co-ordination behaviour of different metal atoms with the same ligand.

The structures of two forms of bis(histidino)zinc, one prepared from L-histidine and the other from DL- histidine, have been reported.l*2 The two forms of the cobalt (II), nickel(n), and cadmium(11) complexes have been studied; 3,4 the DL-nickel compound is described here, but a detailed comparison with the other com- plexes will be made later.

EXPERIMENTAL

Nickel carbonate was added to an aqueous solution of DL-histidine and the mixture heated. Carbon dioxide was evolved ; purple bis(histidino)nickel monohydrate crystall- ised after cooling and evaporation of the solution and was recrystallised from hot water. Deep blue crystals of another hydrate also appeared, but they lost water readily in air.

Crystal Data.-Ni(C,H,N,O,),,H,O, M = 385, ortho- rhombic, a = 15-18 f 0.015, b = 13.05 f 0.023, c = 7-72 & 0.02 A, U = 1529 As, D, = 1-67, (by flotation), 2 = 4, D, = 1.673 g. cm.-,, space-group Aba2, Cu-K, radiation, p = 23.5 cmr1.

The cell dimensions were measured from an hOl Weissen- berg photograph, calibrated with copper powder lines, and from an hkO precession photograph (Mo-K, radiation). For intensity measurements a crystal fragment, elongated along [Oli], with approximate dimensions 0.1 x 0.1 x 0.2 mm. was used. Multiple-film Weissenberg photographs

were taken of seven layers about this [Oli] axis. In- tensities were estimated visually ; Lorentz and polarisation corrections, and a spot-shape correction,2 were applied, but not absorption corrections. Because the layers chosen for photography are diagonal with respect to the orthorhombic symmetry planes, equivalent reflections such as hkl and hk j occur on different layers; the ratio of the scales of almost every possible pair of layers could be derived from these “ common ” reflections, and from them a set of layer scale factors was derived. After averaging equivalent reflections, we had measured 864 independent reflections ; 23 were recorded as too weak to observe, and only about 35 within the limit of Cu-K, radiation were not recorded on any film.

Solution and Refinement of the Structure.-The nickel atoms must lie on two-fold axes, parallel to c, in the space group Aba2, and the origin along the c axis can be arbitrarily chosen a t a nickel atom. A three-dimensional electron-density series was calculated, using those terms for which phases could be derived from the nickel positions. In interpreting this we had to choose as atoms one out of every four peaks related by the false symmetry mmn. Six atoms, in addition to the nickel, were found and used to calculate phases for the second three-dimensional electron- density series; all atoms except hydrogen were then used for a structure-factor calculation (R = O-lS), and a difference electron-density series.

Least-squares refinement was then commenced using a block diagonal approximation. Twelve cycles of refine- ment were carried out of which the first seven produced very significant improvements and the last five did not. Hydrogen atoms a t the stereochemically expected positions in the histidine were included in F, but were not refined. Anisotropic vibration parameters were used for nickel throughout, and were introduced for carbon, nitrogen, and oxygen atoms in the fifth cycle. After the sixth cycle R was 0.096.

A t this stage the vibration parameter in the y direction of the water molecule oxygen atom was very large; this atom had been placed on the two-fold axis, but its hydrogen-bonding pattern is not particularly satisfactory (see Figure 3). It seems more likely that it occupies at random one of two positions just off the two-fold axis. In the seventh cycle, therefore, it was replaced by two half oxygen atoms with isotropic vibration parameters. Because these two oxygen atoms overlap, their positions are not very well defined; in the last cycle of least squares refine- ment the calculated shift (0.012 A) was slightly greater than

1 R. H. Kretsinger, F. A. Cotton, and R. F. Bryan, Acta

* M. M. Harding and S. J. Cole, Acta Cryst., 1963, 16, 643.

3 K. A. Fraser, H. A. Long, R. Candlin, and M. M. Harding,

4 R. Candlin and M. hl. Harding, following Paper. Cvyst., 1963, 16, 651. Chem. Comm., 1965, 344.

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416 J. Chem. SOC. (A), 1967

Observed and calculated h k

J P o l la 0 0

2 205 192 4 8 0 74 6 61 57 8 11 9

0 2 0 122 127 2 190 228 4 136 123 6 6 7 60 8 24 24

0 4 0 29 27 2 126 125 4 127 134 6 4 8 44 8 29 32

0 6 0 09 99 2 132 136 4 43 40 6 29 33 tl 29 27

0 0 2 32 31 4 45 46 6 49 50 0 5 5

0 10 0 35 46 4 31 33 6 17 16

0 12 0 0 7 2 10 17

0 14 2 21 16 4 14 13

1 1 i 144 170 3 17 17 5 56 52 7 29 26 9 7 0

1 2 2 102 107 4 61 58 6 9 9 8 6 6

1 3 1 11 13 3 112 lib 5 5 1 4 6 7 25 25 9 14 15

1 4 0 7 2 68

4 l? 12 6 in 10 0 7 6

1 5 1 60 58 3 8 3 03 5 9 10 7 16 17 9 2n 19

2 36 3 4

1 6 0 19 15 2 39 35 4 10 10 6 24 23 8 15 13

1 7 1 65 63 3 1 4 16 5 35 36 7 2n 21 9 3 5

1 0 2 4 9

h k IF01 l F c l

4 15 15 6 12 11 0 6 7

1 9 3 10 13 5 38 39 7 14 14

1 10 0 16 20 4 12 13

1 11 1 26 29 5 7 7

1 12 0 13 13 2 10 10

1 13 1 5 3 3 27 29 5 6 10

1 14 2 6 6 4 3 4

1 15 3 7 7

2 0 0 79 71 2 57 56 4 45 42 6 69 61 a 10 9

2 1 1 77 02 3 90 04 5 13 9 7 7 0 9 3 2

2 2 0 21 14 2 32 34 4 47 45 6 35 31 0 10 15

2 3 1 0 3 79 3 2 2

7 9 9 9 4 5

2 4 0 44 43 2 114 117 4 48 51 6 15 13 0 20 19

2 5 1 57 52 J 14 13 5 11 13 7 15 13 9 7 6

2 6 0 5 9 65 2 70 71 4 35 37 6 12 14 0 12 11

2 7 1 22 23 3 19 20 5 39 30 7 10 10 9 2 3

2 8 2 12 12 4 39 30 6 46 42 0 3 4

5 14 14

2 9

I 3 5

TABLE 1

structure factors, in electrons per unit cell

2 10 0 35 47 4 23 21 6 21 19

2 11 1 16 20 5 7 8

2 12 0 27 30 2 40 4 3

2 13 1 15 14 3 7 0 5 3 5

2 14 2 37 30 4 26 23

2 15 3 15 15

3 1 I 28 25 3 23 19 5 57 54 7 26 24 9 5 7

3 2 0 122 117 2 46 46 4 27 24 6 4 4 0 6 9

3 3 1 43 45 3 50 60 5 21 20 7 20 18 9 17 16

3 4 0 47 47 2 25 23 4 19 20 6 16 14 8 3 3

3 5 1 37 36 3 71 7 0 5 14 16 7 is 16 9 14 14

3 6 0 40 37 2 17 15 4 13 14 6 12 12 0 9 9

3 7 I 46 46 3 25 25 5 42 41 7 1 5 16

3 0 2 11 10 4 11 12 8 2 3

3 9 3 20 10 5 35 37 7 19 18

3 10 n 9 10 4 12 14 6 11 9

3 11 1 35 43 5 16 16

3 12

h k IF01 P C l

0 26 27 2 10 8

3 1s 1 35 33 3 41 40 5 7 9

3 14 2 0 6 4 6 6

3 15 3 23 19

4 0 0 114 115 2 112 00 4 57 55 6 52 4 0 0 0 7

4 1

3 37 35 5 6 4 7 6 5 9 4 4

4 2 0 183 102 2 59 50 4 64 64 6 30 20 0 il 12

4 3 1 23 20

5 15 14 9 5 5

4 4 0 38 33 2 134 120 4 46 49 6 26 26 0 25 26

4 5 1 4 0 36 3 6 5 5 11 12 7 9 9 9 4 6

4 6 0 6 4 70 2 36 34 4 63 61 6 29 31 0 15 15

4 7 1 14 12 3 3 3 5 19 20 7 4 3

4 8 2 61 63 4 21 22 6 27 20 0 0 9

4 9 3 11 11 5 14 15 7 2 4

4 10 0 55 69 4 37 3 0 6 26 27

4 11 1 6 6 5 7 6

4 12 0 6 1 2 45 46

4 13 1 6 6 3 11 9

1 55 5a

3 2a 2a

h k J IF01 l F c l 5 7 10

4 14 2 26 20 4 22 19

4 15 3 9 7

5 1 1 55 57

5 34 32 7 16 15 9 4 3

5 2 0 73 60 2 20 20 4 14 13 6 10 16 0 4 5

5 3 1 40 42 3 55 53 5 12 11 7 9 10 9 12 li

5 4 2 17 15 4 14 14 6 9 8

5 5 1 12 ii 3 57 62

7 16 16 9 6 0

5 6 0 4 5 2 3 9 38 4 9 9

3 6 8

5 2a 20

6 7 0 a 10 9

5 7 i 54 55 3 11 12 5 20 21 7 15 16

5 8 2 20 19 4 9 11 a 2 3

5 9 3 9 9

7 13 13 5 16 ta

5 10 0 12 15 2 2 2 4 5 5 6 13 13

5 11 1 5 7 5 27 27

5 12 0 15 17 2 4 3

5 13 1 21 11) 3 24 21 5 2 5

5 14 2 5 5 4 3 2

5 15 3 10 9

6 0 0 97 94 2 53 55 4 61 56 6 48 4a

h k IF01 l F c l

8 11 13

I 6 1 45 47

3 21 19 5 5 4 7 11 11 9 4 4

6 2 2 0 140 05 130 84

4 44 44 6 28 27 8 15 1 4

6 3 1 03 77 5 3 31 36 30 36

7 6 6 9 3 3

6 4 0 31 34 2 96 93 4 57 60

8 16 17

6 5 1 35 32 3 69 66 5 8 9

9 3 4

6 6 0 48 5 0 2 46 49 4 51 48 6 28 30 8 12 12

6 7 1. 32 33 3 33 32 5 15 15 7 3 3

6 8 2 43 41 4 11 13 6 l? 10 8 8 9

6 9

5 4 4 7 9 10

6 10 0 20 22 4 27 27 b 20 19

6 11 1 29 31 3 7 11 5 20 21

6 12 0 3 1 2 27 22 4 17 23

6 13 1 4 3 3 24 24 5 2 2

6 14 2 25 19 4 6 6

6 15 3 11 9

6 ia ie

7 8 9

3 19 ia

1 7 1 02 83

3 65 62 5 64 59 7 29 20 9 a ii

7 2

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Inorg. Phys. Theor. 417

TABLE 1 zontinued)

h k l F o l l F c l

7 3 ;

0 4 0 94 93 2 45 45 4 41 4 4 6 29 26 0 17 17

0 5

3 10 10 5 22 25 7 0 0

i ia 10

0 6 0 24 20 2 60 61 4 37 37 6 21 21 8 11 12

0 7 1 35 37 3 16 17 5 15 10 7 7 7

0 0 2 33 33 4 27 31 6 20 19

0 9 3 22 22 5 9 10

8 10 0 25 24 4 15 15 6 10 10

h k IF01 I F C I

1 15 11 3 12 13

12 0 0 30 22 2 53 4 0 4 24 23

It k h k

0 70 65 3 15 16 5 6 7

10 10 0 21 16 2 21 23 4 20 10 6 11 13

2 5 7 4 13 13 6 11 10

13 5 1 39 35 3 12 12 5 13 12

2 2 7 25 4 9 7 6 26 24

’ 25 20 J 20 21 5 19 18 7 11 11

9 0

8 2 4

7 3 1 77 77 3 59 59 5 20 25

2 12 14 4 9 10 6 5 6

12 1 1 15 15 3 32 3 0

13 6 0 3 7

10 11 1 14 15 7 26 26

9 16 19

7 4 0 53 47 2 21 18 4 0 9 6 5 5

7 5 1 31 28 3 56 56 5 37 36 7 24 23

7 6 0 44 44 2 29 29 4 24 22 6 9 9

7 7 1 5r) 4 0 3 31 33 5 25 27 7 14 16

7 0

9 9 3 7 0 5 2 3

5 5 7 7 5 5

12 2 0 21 17 2 12 0 4 26 23 6 18 15

12 3 1 0 0 3 19 18 5 6 7 7 6 6

12 4 0 3 2 2 25 22 * 15 10 6 20 19

12 5 1 9 9 3 17 17 5 4 4 7 4 4

12 6 0 46 42 2 11 11 4 16 16 6 11 10

12 7 1 0 10 5 23 25 5 7 9

2 26 28 4 15 15 6 0 9

13 7 1 12 12 3 23 23 5 12 12

0 13 15 2 12 12 4 6 6

13 8

13 9 1 7 7 3 21 20 5 0 9

13 1 0 0 2 2 2 5 7 4 1 5

3 12 12

7 11 13 5 17 17

10 12 0 29 25

9 10 2 24 10 4 12 14

10 13 1 3 3 3 6 5

o i i 13 4 14 14 6 2 3

9 11 1 2 0 19 3 1 0 12 5 7 7

9 12 0 15 13 2 20 15 4 1 . 3

9 13 1 19 15 3 19 1 7

9 14 ? 4 3

10 0 n 77 79 2 60 59 4 4 5 4 4 6 2fl 19 8 11 12

10 1 1 29 30 3 17 18 5 24 25 7 10 11

10 14 2 14 13

11 1 1 53 49 3 31 2 0 5 8 10 7 8 9

11 2 0 57 54 2 4 1 4 7 7 6 7 0 0 0 11

11 3 1 6 3 3 30 25 5 36 31 7 12 13

11 4 0 17 10 2 9 9 4 6 5 6 7 6

13 11 1 2s 22 3 5 5

2 13 13 4 . . 5 5 13 12

0 9 0 2 3 3

0 3 6

7 9 11 1 12 12 3 19 27

3 21 21 5 17 10 7 9 0

14 0 0 26 22

2 4 56 39 50 39 b 22 22

14 1

0 12 0 3 4 30 2 20 15 4 13 16

7 10 0 38 43 4 14 13 6 7 8

7 11 1 21 2 1 3 20 27 5 16 15

7 12 0 3 4 2 7 7 4 9 13

f 13 1 24 19 3 2 0 16 5 5 7

7 14 2 12 11 4 5 4

0 0 0 1 0 0 100 2 b @ 59 4 75 73 6 39 41 8 7 7

8 1 1 39 37 3 24 24 5 22 21 7 0 8 9 5 5

0 2 0 59 60 2 93 91 4 46 45 6 3 0 29 0 22 21

0 3 1 9 10 3 413 50 5 9 ti

12 a 0 0 5 2 37 35 4 23 24 6 7 6

12 9 1 11 12 3 0 8 5 3 5

1 11 11 3 7 0 5 4 4

0 13 1 23 20 3 5 3

10 2 0 39 4 0 2 56 52 4 45 40 6 25 23 0 10 12

10 3 1 23 22 3 25 25 5 5 6

11 5 1 20 26 3 20 15 5 20 10 7 13 13

7 1 3

14 2 0 5 0 53 2 52 45 4 39 37 6 19 21

14 3 1 17 16 3 7 0 5 17 10

2 0 40 76 70 43 4 25 25 6 10 19

1 4 4

1 4 5 1 12 13 3 17 16 5 6 9

14 6 2 0 47 32 43 32

4 23 23 6 10 16

1 4 7 1 7 10 3 0 3 5 2 4

1 4 a

0 14 2 21 10

9 1 1 21 20 3 29 20 5 27 25 7 15 14

9 2 0 16 19 2 4 5 46 4 5 5 6 22 22 8 8 9

9 3 1 40 39 3 35 33 5 25 21 7 14 12

11 6 0 41 37 2 19 2 0 4 10 10 6 10 10

11 7 1 35 30 3 21 21 5 15 14 7 9 11

12 10 0 40 39 2 20 23

10 4 0 62 64 ? 51 50 4 40 3 7 6 21 20 a 6 0

1 7 8 3 13 15 5 5 5 7 2 3

0 59 59 2 52 4 8 4 24 23 6 11 11

10 5

10 6

10 7 1 46 47 3 22 24 5 0 11 7 4 6

10 0 0 19 21 2 24 20 4 25 26 6 22 22

10 9 1 15 21

4 1 5 1 6

12 11 1 5 4 3 7 7

11 0 0 5 4 2 10 9 4 10 11 6 5 5

12 12 0 23 18 2 26 23

12 13 1 5 3

13 1 1 12 10 3 24 20 5 10 7 7 10 9

13 2 0 10 16 2 10 18 4 15 15 6 14 15

13 3 1 20 10 3 13 10 5 23 20 7 12 13

13 4 0 0 8

11 9 ~- 1 22 25 3 32 32 5 14 17

9 4 0 0 7 2 16 17 4 25 24 6 7 0

9 5 1 53 49 3 33 33 5 17 16 7 7 6

9 6 0 43 47 2 7 7 4 9 10 6 17 20 8 4 5

11 10 0 30 31 2 5 7 4 0 3

11 11 1 36 30

5 9 12 3 17 10

0 2 0 2 28 28 4 23 26

11 12 0 9 8 2 3 3 4 1 2

11 13

14 9 1 8 10 3 7 6

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418 J. Chem. SOC. (A), 1967

It k

0 16 1 5 2 11 1 2

14 11 1 11 9

15 1 1 4 2 3 4 3 42 38 5 1 6 1 5

15 2 0 18 21 2 16 17 4 5 5 6 2 2

15; 3 1 4 5 40 3 28 2 2 5 2 1 20

1 5 4 0 8 8 2 5 6 4 3 3

15 5

h k 1 IF01 l F C l

1 2 9 25 3 1 4 1 2 5 1 9 2 1

15 6 0 7 8 2 0 0 4 6 6

1 5 7 1 1 7 .13 3 20 1 9

15 8 0 8 7 2 4 3 4 3 5

15 9 1 1 0 1 0 3 1 4 16

15 10 0 2 1 2 4 5

16 0 0 2 2 1 6 2 25 20

4 20 1 8

16 1 1 6 8 3 8 0 5 5 6

16 2 0 20 1 5 2 30 25 4 1 2 1 0

3 11 il 5 5 6

16 3

16 4 D 31 27 2 7 4 4 17 16

1 1 2 1 2 3 9 8 5 2 4

0 10 4

16 5

16 6

2 16 13

(Continued) h k

1 P o l l F c l 4 1 0 1 0

16 7 1 4 5

3.6 0 0 18 18 2 16 1 4

1 6 9 1 3 4

1 7 1 1 2 2 3 17 14

0 10 9 2 . 4 5 4 6 7

1 7 2

1 7 3 I 20 15 3 5 4

6 3 3 2 9 9 4 4 4

17 4

h k 1 IF01 l F c l

1 1 2 8 3 6 4

17 6 0 6 5 2 5 6

17 7 1 1 4 11'

17 6 0 1 2

10 0 0 2 6 2 20 15 4 19 2 0

1 10 9 3 7 8

18 I

10 2 0 19 15 2 18 15

1 4 .3 18 5

h k IF01 I F C

3 3 4

1 8 4 0 3 1 2 9 2 8 5

1 0 7

0 9 7

1 4 2

0 10 1 0 2 6 8

i 11 11

2 12 1 2 4 6 6

1 7 7 5 2 1 20 5 8 9

18 5

18 6

19 i

19 2

19 3

is 9

TABLE 2

Positional and vibrational parameters. The numerals in parentheses are lo4 times the estimated standard deviations of The vibrational parameters, 02, are mean square vibration amplitudes (in Hi2) relative to The hydrogen parameters are those used in the structure-factor calculation; they have

the positional parameters. the crystallographic axes. not been determined

X Y z 1 0 3 U 2 ~ ~ 1 0 3 U 2 ~ ~ i 0 3 0 ~ , , 103Pea ioWtl 103Ualt 0

O.OSOO( 3) 0.0962(3) 0.1 886(4) 0*2031(3) 0.1 7 19 (3) 0.28 1 O( 3) 0-0285(3) 0.1351 (2) 0.2598( 3) 0.0245 (2) 0.1207 (2)

0.0859 0.2016 0.2309 0.1407 0.3051 0.3475 0.0613

0.00 12 (2)

.0.0250

0 -0*1845(4) - 0.1801 (4) - 0.1361 (5) - 0*0342(5)

0*1167(6) 0.0151 (6)

0.03 15( 3) 0*1095(4)

-0.1 194(4)

- 0.12 10( 3) - 0*2488(3) -0*0161(6) - 0.2499 -0.1326 - 0.1897

0.1835 0-1627

- 0.0042 - 0.0897 -0.1579

0 0.1 122 (9)

- 0.0836(9) -0.1201(9) - 0.0431 (9)

- 0.0043( 16) - 0.1747(7)

0.06 5 7 (9)

0*0057( 10) 0.0577 (8) 0.1 7 54 (6) 0.20 1 O ( 6) 0.4 7 1 9 (9)

- 0.1328 -0.2518 - 0.0639

0.1159 0.0977

- 0.0234 - 0.2838 - 0.2 151

the estimated standard deviation (e.s.d., 0.011 A), while all other atom shifts were less than half the corresponding e.s.d.s. Reflections with IFI<80 were given weight 1, and others weight (80/IF/)2 in the least-squares refinement. The atomic scattering factors used for carbon, nitrogen, and oxygen were those of Berghuis et u Z . ~ (the carboxyl oxygens being treated as Oa-), for hydrogen that of McWeeney,6 and for Niff that of Thomas and Umeda corrected for anomalous dispersion.8 The final R factor, for observed reflections only, is 0.082.

Observed and calculated structure factors are given in

J. Berghuis, I J . M. Haanappcl, M. Potters, B. 0. Loopstra, C. H. MacGillavry, and A. L. Veenendaal, Acta Cryst., 1955, 8, 478.

29 20 32 37 20 33 24 33 23 31 33 36 42 22 34 34 32 38 38 25 25

24 27 18 37 38 31 55 28 33 51 35 25

37 0 0 68 5 3 60 -3 2 59 1 14 62 16 2 59 -1 -7 66 9 0 47 -8 2 53 -7 2 60 17 - 10 41 1 1 59 13 8

(Isotropic: half atom) Isotropic, located on C(2)

, ,, C(3) I > C(3) , I C(5) ,, N(3) ,, (76) ,, N(1)

,, , I N(1)

0 0

-5 11 6

-2 -3 -4 -6 - 17

6 8

Table 1, positional and vibrational parameters in Table 2, and bond lengths and angles in Table 3 and Figure 1. Positional standard deviations were estimated from the inverse of the last least-squares matrix.

DESCRIPTION AND DISCUSSION OF THE STRUCTURE

The crystal contains molecules of bis-(D-histidino) - nickel and bis-(L-histidino)nickel, related to each other by glide planes. In each molecule the nickel is octa-

6 R. McWeeny, Acta Cryst., 1951, 4, 513. L. H. Thomas and K. Umeda, J . Chem. Phys., 1957, 26, 293.

8 C. H. Dauben and D. H. Templeton, Acta Cryst., 1955, 8, 841.

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419 Inorg. Phys. Theor.

hedrally co-ordinated to two nitrogen atoms and an oxygen atom of each histidine group. Their distances

TABLE 3

Bond lengths (A) and angies Ni-K (1) 2.106 Ni-N(2) . .... . . ..... ...... 2.091 Ni-0 (1) . . . . , . . . . . . . . . . . . . 2.1 13

C(l)-C(2) ..... , ..... . ...... 1.532 C(2)-C(3) ...... ............ 1.542 C(3)-C(4) .................. 1.473 C(4)-N(2) ...... ......... 1.393 C(4)-C(6) ............... 1.379 C(5)-N(2) ...... .... ..... 1.329 C(5)-N(3) ............... 1.338 C(6)-N(3) ............... 1.360 C( 1)-O( 1) 1.278 C(1)-0(2) ............... 1.247 C(2)-N(1) . . . . .... . ..... . 1.475

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

N( l)-Ni-N(2) . . . . . . . . . N( 1)-Ni-O( 1) . . . . . . . . . N (2)-Ni-O ( 1) . . . . . . . . . N (1)-Ni-N'( 1) . . . . . . . . . N (2)-Ni-N'( 2) . . . . . . . . . O( 1)-Ni-0'( 1) . . . . . . . . . N( l)-Ni-N'(2) . . . . . . . . . N( 1)-Ni-0'( 1) . . . . . . . . . N(2)-Ni-O'( 1) . . . . . . . . . Ni-N (1)-C( 2) . . . . . . . . . Ni-N(2)-C(5) . . . . . . . . . Ni-N (2)-C (4) . . . . . . . . . Ni-0 (1)-C (1) . . . . . . . . .

87.6" 79.7 87.8

100.3 177.6 100.3 94.0

178.3 90.7

103.6 125.7 126.9 110.9

Hydrogen bonds N(3)-H . . . O(2) at Q - x, -3 + y, z K(l)-H . O(2) at -x , -6 - y , - 4 + z... 3.00 O(1) * . * . . H-0, at x , y, z ..................... 2.70 O'(1) . . . . . H-0, at x , y, z ..................... 2.93 N( l ) -H . - - 0, a t x, y , -1 + z ............... 3.08

...... 2.82 .&

Estimated standard deviations Ni-N, Ni-0 ... 0.008 A Angles at Ni ......... 0.5" C-C ............... 0.016 Other angles ......... 0.8 C-N .. .... .. . ..... . c-0 . ... . . . . . . ... . .

0.014 0.013

from nickel are equal, within the accuracy of the determination, and the angles between the bonds are all

bond lengths are the same within 0.02 A (Le . , one e.s.d.) except for C(1)-0(1) which is 0-035A longer in the nickel compound than the zinc. This difference need

FIGURE 1 One molecule of bis(histidin0)nickel

not be significant, but it is in the expected direction since Ni-O(1) is a full bond but Z n * - * 0(1) is only a weak association. The bond lengths in the nickel complex are also in agreement, to within 0.03& with

TABLE 4

Planarity of various groups of atoms. The equation of the best plane through each set is A x + By + Cz + D = 0

A B C 12 Iniidazole . . . . . . . . . 0.008 -5.153 7.091 0-132

Imidazole . . . . . . . . . 0.021 - 5.002 7.124 0.118

Carboxyl ......... -11.161 -8-638 -1.121 -0.576

14.702 3.236 0.000 0.000

- 1.912 8.205 5.922 -0.013 Sections of nickel

octahedron

within 10" of the ideal values of 90 or 180". The Ni-N and Ni-0 distances are in agreement with those found in other octahedral complexes of nickel involving amino-nitrogen or carboxyl oxygen atoms, for example, bis-( P-a1anino)nickel dihydrate where Ni-0 = 2.14 ( 0 = 0-02), Ni-N = 2.10(0-03), Ni-OH2 = 2.17(0.02) A.

To allow the regular octahedral co-ordination, the conformation of the histidine group has changed from that in bis(histidin0)zinc pentahydrate,2 by small rotations about carbon-carbon single bonds. The interbond angles are all the same within lo, and the

P. Jose, L. M. Pant, and A. B. Biswas, Acta Cryst., 1964, 17, 24.

lo J . Donohue and A. Caron, Acta Cryst., 1964, 17, 1178.

Atoms defining the plane and their displacements from i t in .& C(4) C(5) C(6) "2) N(3) 0.005 -0*002 0.026 0.011 -0.021

(73)

C(4) N(2) "3) - 0.017

-0.014 ?!%7 ?%)18 0.004 -0.013 0 (2)

N(1) "(1) ?(*'do0 "d."doo %oo 0~000

O;!& 0.032 -0.032 Ni 0(1) 0.000 -0.032 Ni 0(1) "2) "(1) "(2)

-0.013 -0.014 0.020 -0.014 0.021

those in histidine hydrochloride monohydrate,1° again with the exception of C(1)-0(1) which is the same length as in the zinc complex. There are larger differences in the angles (3") and the conformation is quite different .

The imidazole group is planar, but the nickel atom lies 0-132A out of its plane. The carboxyl group including C(2) is planar, but N(l) lies 0.33 A out of this plane, a much bigger displacement than in bis(histidin0)- zinc. Details of the various planar groups are given in Table 4.

Figure 2 illustrates the packing of molecules in the crystal lattice. Hydrogen bonds between one bis- (histidino)nickel molecule and another hold the molecules

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420 J. Chem. SOC. (A), 1967

C

0

FIGURE 2 Projection down the b axis showing the packing of molecules. The nickel atoms of molecules shown in heavier lincs Hydrogen bonds linking molecules of bis(histidin0)nickel are shown as dashed line; and those are a t y = 0; the others are a t y = +.

involving water molecules as dotted lines; the hydrogen bond system is only shown for water molecules a t y = ca. 0

d

Ni FIGURE 3 Environment of 0, in its position slightly displaced

from the two-fold axis. The alternative position is shown as a dotted circle. All the atoms shown except O(2) and O’(2) are coplanar within 0.07 A. The water molecule hydrogen atoms are required for the bonds 0,-H - 0 ( 1 ) and 0,-H - * - O’(1) and a hydrogen atom from the amino-group is available for the bond N(l)-H - - - 0,

firmly in sheets perpendicular to c, but less rigidly in the c direction. As a result the mean-square amplitudes of

vibration of all atoms are considerably greater in the c direction than perpendicular to i t (Table 2).

The water molecule participates in a loose network of hydrogen bonds joining molecules in the c axis direction. Figure 3 illustrates this part of its environment, and shows that some of its interbond angles are far from the optimum for hydrogen bonds, particularly N(l)-OkV-N’(l). The small displacement of 0, from the two-fold axis suggested during the least-squares refinement allows 0, to form a reasonably good hydrogen bond to N ( l ) and none to N‘(l) , or vice zleysa.

But in addition to these neighbours shown in Figure 3 there are two CH groups [imidazole C(6)] a t 3.31 and 3-37w, making, with the two nitrogen and two oxygen atoms, a distorted octahedron around 0,. These must be van der Waals contacts, and they explain why 0, is so firmly held in the crystal despite the rather poor hydrogen-bond geometry.

We acknowledge financial assistance from the S.R.C. and a research studentship to K. A. F. We thank Rlr. H. A. Long for the initial preparation of bis(histidin0)- nickel, Dr. R. Diamand for his least-squares refinement programme, and Dr. L. Hodgson for a bond length and angle programme. The computations were done on the Atlas computers of Manchester University and of the S.R.C. (at Chiiton, Berks.) and we thank these establish- ments and the Edinburgh University Computer Unit for assistance.

[6/1022 Received, August l l t h , 19661

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