1782 Inorganic Chemistry, Vol. 10, No. 8, 1971
(CH3)2SI2FeIIclosely resemble those found in the analogous Ni(II) specie^.^,^ In summary, [SP(CH3)2NP(CH3)2S]2Fe11 is the first confirmed example of a simple tetrahedral complex with an FeSI core. There is no ready explanation as to why the Fe(I1) center has a tetrahedral (rather than square planar) coordination sphere, except that it may be noted that an S-Fe-S angle of 109" 28' affords a more strain-free ligand geometry than would the squareplanar angle of 90'.
V
Figure 2.-Packing
of [SP(CHS)~NP(CH~)~S]~F~~I molecules in the unit cell.
the energetically unfavorable boat conformation. In particular, we suspect that there are interactions between hydrogen atoms associated with the CH3(axial) . .CH3(axial) contact, C(6). . .C(8) = 3.629 (13) fi (see Figure 1). [The CH3(eq). . sCH3(eq) contact, C(5). *C(7),is 5.192 (14) f i . ] All other features of the structure of [SP(CH3)2NP+
The Crystal Structure No intermolecular contacts of less than 3.5 A were found. [This does not, however, include those involving hydrogen atoms, which were not detected in this analysis.] It is, nevertheless] clear that the crystal consists of independent molecular units of [SP(CH3j2NP(CH3)2S]2Fe11, held apart by normal van der Waals forces. The packing of molecules within the unit cell is illustrated in Figure 2 . Acknowledgments.-We thank Professor A . Davison and Mrs. E. S. Switkes for supplying samples of the title complex. This work was supported by the Advanced Research Projects Agency and the National Science Foundation (GP-26293). J. W. gratefully acknowledges receipt of a Graduate National Fellowship from Harvard University for 1967-1970.
THE RESEARCH SCHOOL OF CHEMISTRY, !LUSTRALIAN N A T I O N A L U N I V E R S I T Y , C A N B E R R A , AUSTRALIA
COXTRIBUTION FROM
The Crystal and Molecular Structure of Racemic (4-(2-Aminoethy1)-1,4,7,1O-tetraazadecane)azidocobalt(III)Nitrate Hydrate BY IAN E. MAXWELL* Received February 9,1970 The crystal and molecular structure of racemic (4-(2-aminoethyl)-l,4,7,lO-tetraazadecane)azidocobalt~III)nitrate hydrate, sym- [Co(trenen)N3]( N 0 3 )eH10, ~ has been determined from three-dimensionalnX-ray data collected by count5r methods. The compound crystallizes in space group P21/c ( C2h5; no. 14), with a = 8.32 (1)A, b = 7.64 (1) A, c = 27.69 ( 3 ) A, p = 96.3 (3)", and 2 = 4. Measured and calculated densities are 1.66 ( 2 )and 1.64 (1) g Full-matrix least-squares techniques were used to refine the structure t o a final residual R = 0.068 for 2030 independent nonzero reflections. The crystal is composed of sym-Co(trenen)Ns2+cations, Koa- anions, and water molecules which are held together by electrostatic forces and hydrogen bonds. The coordination at the metal ion is octahedral with the polyamine ligand coordinated quinquedentate and the azide ion occupying the remaining coordination site. The bifurcated structure of the ligand, trenen, and the mode of coordination have been determined. Ligand chelate ring conformations and the bonding requirements of the azide ion are discussed. Also the relationship between the structure of sym-Co(trenen)Ns2+ and the base hydrolysis studies of the related chloro complex are discussed.
Introduction As part of a general study on the stereochemistry and mechanisms of hydrolysis of complexes of the type CoNsX2+(where Nb is a multidentate amine, a monodentate amine] ammonia, or a combination, and X is an acido group), four Co(tetraen)X2+(tetraen = tetraethylenepentamine) complexes were prepared and characterized. The commercially available linear tetraen (Union Carbide) was known to contain a considerable percentage, of some impurity, probably a
* Address correspondence t o Koninklijke/Shell Laboratorium, Badruisweg 3, Amsterdam-N, Netherlands. (1) P. A. Marzilli, Ph.D. Thesis, Australian National University, 1968.
branched-chain isomer. This posed the problem of deciding not only between topological isomers in the complexes but also between ligand isomers. In view of the very large number of isomeric possibilities, it was very difficult to make unequivocal structural assignments to the isolated complexes. Detailed structural knowledge is essential to any comprehensive study of the mechanisms of hydrolysis of these compounds. Further, the conformations of the chelate rings in these types of complexes are of interest in determining the factors governing the geometries of multidentate amine complexes. Such information could be provided by a crystal structure analysis and
Inorganic Chemistry, Vol. 10, No. 8, 1971
sym- [C~(trenen)Ng](NO~)~. HzO
this paper describes the results of an X-ray structural analysis on a Co(tetraen)Ng2+ complex. The azido complex is known to be structurally related to the chloro complex isolated as the first fraction from the reaction mixture, Therefore the results of this analysis will be relevant to the kinetic studies on the chloro complex. Also accurate structural data on coordinated azide is sparse and additional data might aid in defining the bonding requirements for coordinated azide ion. Suitable single crystals of the racemic complex were obtained as the dinitrate salt. Experimental Section Crystal Data.-rac- [Co(tetraen)N3](NO3)z.Ha0 crystallized in well-formed air-stable oratige crystals. The unit cell is monoclinic with a = 8.32 (1) A, b = 7.64 (1) b, c = 27.69 (3) b, p = 96.3 (3)", V = 1749.6 A3, d,, = 1.66 (2) g c ~ n (by - ~ flotation in bromoethane-ethanol), Z = 4, d, = 1.64 (1) g cm-3 for C8H2&J1007Cowith FW 452.4, ~ c =~ 86.2 K cm-'. ~ From systematic absences of reflections (1201 absent for Z = 2n 1, OkG absent for k = 2n 1) the space group was determined to be P21/c ( C2h6; no 14). Unit cell dimensions were calculated from 0 measurements on high-angle reflections using an equiinclination diffractometer and Ni-filtered Cu K a radiation [X(Cu K a l ) 1.5405 b, X(CUKaa) 1.5443 A]. X-Ray Data Collection and Reduction.-Two crystals of dimensions 0.10 X 0.05 X 0.04 mm and 0.07 X 0.20 X 0.04 mm (parallel to axes a , b , and c, respectively) were mounted about the a and b axes, respectively, for data collection. Data were collected on an automated Buerger-Supper equiinclination diffractometer using Ni-filtered Cu K a radiation from a fully stabilized X-ray generator. The control program was an early version of that described by Freeman, et aZ.2 The reflection indices hkZ, setting angles 4 (crystal) and y (counter), and scan range w were input from punched paper tape. The background and peak intensities B1, P,Ba were recorded under computer control, using a sequence of operations analogous to those previously d e ~ c r i b e d . ~ The angle subtended a t the crystal by the counter aperture was increased with increasing p in the range 2' 50'"" 50'. A constant scan of B"/min was used and the scan range was generally 3", being increased for very extended reflections. Attenuation of the X-ray beam was not necessary since the maximum observed count rale was within the linear range of the counter. Reflection data were collected in the range 10' y 140" for the zone HkO and levels hKZ and hK1 (0 6 K 6). The net count I(hkZ) for each reflection was calculated as I(hkZ) = P ( B I B J )where P is the spot count and B1 and B Zare the first and second background counts. A reflection was 'considered unobserved if I ( h k l ) < 2(B1 Bp)'/z. Lorentz-polarization corrections were applied and estimated standard deviations were calculated by the method of Hoard and J a c o b ~ o n using ,~ values of 0.02, 0.05, and 0 for KT, KB, and KD,the estimated errors in peak count, background count, and correction for crystal decomposition, respectively. Absorption corrections were applied by the method of Coppens, Leiserowitz, and Rabinovich .6 The grids used were 2 X 10 X 6 and 4 X 10 X 2 (parallel to a , b, and c) for the a- and b-axis crystals, respectively. Calculated transmission coefficients were in the ranges 0.71-0.77 and 0.55-0.72 for the a- and b-axis crystals, respectively. Scale factors between layers were calculated by a least-squares procedure6 and indicated some decomposition of the b-axis crystal (maximum lo%).. A total of 2739 independent reflections were obtained of which 709 were unobservably weak. Solution and Refinement of the Structure .-The structure was solved using a sharpened Patterson synthesis and the usual Fourier analyses. One molecule of water of crystallization was located from a ( F o - F,) synthesis calculated in the final stages of solution of the structure. Full-matrix least-squares refinement was carried out minimizing the function Zw(lFol - s1Fc1)2where
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Figure 2 .
in Table 111. The nitrogen atoms of each cation make seven hydrogen bonds with the oxygen atoms of four neighboring nitrate anions. Each nitrate ion hydrogen bonds to two adjacent complex cations and each water molecule H bonds to two adjacent nitrate groups. The
H-bonding scheme is complex and is shown partly in Figure 2. Closest nonbonded contacts occur between cations and nitrate anions and are t s follows: C(6)-0(7)"'; 3.16 A; N(7). . .0(6)"', 3.19 A; N(7). .0(3)'", 3.20 A;
1786 Inorgunic Chemistry, Vol. 10, No. 8, 1971
IANMAXWELL TABLE I1
FRACTIONAL ATOMIC P O S I T I O N A L Aton
104x
104z
PARAMETERSa-C A K D !iNISOTROPIC 104ilI
I O ~ P ~ :q4.-3j ~
N(8) * .0(3)'", 3.26 A ; C(1) * .0(2)"', 3.18 A ; C ( 8 ) . * 0(3)", 3.30 A; C(7) * .0(6)'", 3.30 A (symmetry transformations are given in footnot: a of Table 111; estimated standard deviations, 0.01 A). Description of the Complex Cation.-Perspective views of the complex are given in Figures 1 and 3. +
Figure 3.
Clearly, the tetraen ligand is not the linear form but a branched-chain isomer, 4-(2-aminOethYl)-1,4,7,10 tetraazadecane (abbreviated trenen). The ligand is coordinated quinquedentate in a symmetrical manner about the metal ion. If the puckering of the chelate rings is neglected, there is a mirror plane through the coordination plane containing the atoms x(2))N(4), N(S), N(6), and Co. For this reason the complex has been named' sym-Co(trenen)N32+. Azide ion is coor-
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dX
1odt
dinated to the metal ion a t the remainiilg octahedral site. An interesting feature of the complex cation is that the asymmetry of the ion is derived solely from the asymmetric secondary N atom, N(4). Inversion a t this secondary N center produces the enantiomeric form of the complex. Also the chelate rings are puckered and the conforniations are discussed in some detail later. Intramolecular bond distances and angles are given in Tables IV and V. With the exception of one bond all the CoII*-N bond distances are within la of their mean value of 1.967 (3) A. The Co-N(3) bond distance of 1.992 ( 5 ) A is 7a from this mean value. (Estimated standard deviations are given in parentheses right-adjusted to the least significant figure of the previous number.) This bond lengthening might be explained on the basis of unfavorable steric interactions between hydrogens on S(3) and hydrogens on the adjacent chelate rings. Clearly, the cobalt(II1)-azide bond (1.957(6) A) is not significantly different from the cobalt(II1)-amine mean value. However, it differs by 3a from the cobalt(II1)-azide distance of 1.943 ( 5 ) A as foulid in the [ C O ( N H ~ ) ~ N ~crystal ] ( N ~structure." )~ In the azido gioup the x-x bonds are not equivalent but are collinear and the bond angle to the metal ion is 119,0 ( s )compared ~ with 124,8 (210 in c ~ ( N H ~ ) ~ N ~ ~ + . I I The u n e q ~ a azide l bonds in this comp!ex, ~ ( 6 ) - ~ ( 7 ) , 1,209 (7) p1, and N(7)-N(8), 1,152 (7j A,are similar to those found in c ~ ( N H ~ ) ~ N being ~ z + , 1,208 ( 7 ) and 1,145( 7 ) A, respectively." In both structures the (11) G. J. Palenik, Acle Cryslallogr., 17, 360 (1964).
Inorganic Chemistry, Vol. 10, No. 8, 1971 1787
sym- [Co(trenen)N3](N03)~. €I20
TABLE V INTRAMOLECULAR BONDANGLESFOR [Co(trenen)N3](NOa)2*HzO
TABLE111 HYDROGEN BONDSI N THE [Co(trenen)Na]( N O ~ ) ~ . HCRYSTAL" ZO Atoms X - H
....Y
0(7)-H..
. .0(5)
N(3)-H..
. .O(S)viii ..0(6)vi
N(4)- H . .
..0(2)'
N(3)-H..
N(5)- H . .
3 .OO 2.98
..0(4)vi
O(4). ,
Atoms
. .H. .H-
N(S)'I
3.00
l+(5)iv
3.04
Angle (deg.)
Atoms
....0 ( 5 ) - N ( 1 0 )
115
O(7).
O(7)
. . . .C ( 6 ) " - N ( 4 I i i
162
0 [ 7 ) , ,.C(6)iiC(S!ii
iv
iv -N(9)
vi
O(3). ...N(l)vi-C(l)
. . . N ( 1 ) v i -i Cov i i O ( 5 ) . . . . N ( 3 ) i x - COi x O(3).
N(3).
.. . 0 ( 6 y i -
. ..0(6)i-N(!Oli
N(10)v i
!11.1(3) 111.7(5)
94.8(2)
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94.4 (2)
117.4(5)
94.6l.21
109.!(4)
91. 5 ( 2 )
109.3 (4)
106.8(6)
114
CO
115
108.1(5)
110.9(4)
121
N ( 1 ) . , , .0(3)'-
N(9)'
109
106.9(3)
119.0(5)
1 I@
O(3).
107
106.6 (4)
176.4(9)
125
N(3). ,,. O ( S ) v ~ N ( l O ) v u l
V I
ii vii . .. N ( l ) v C(1)
104
118
N(4).
107
O(2)
vi
113
N(S)....0(!)i~N(91iV
N(5)....0(4)vi-
N(l0)"'
127
O(l),,,.N(5)vi-
C(8)"
94
0(4).,.,N(S)iv-
C(8Iiv
109
0(4)....N(S)iv-
CaiV
108
vii
. . .0(2) - N ( 9 ) Y
- Cov i i
. . . N ( 4 ) "ii- C ( 7 ) v i i
....N ( 4 )
A n g l e s w i t h i n NO3-
V
..
vii -C(6)""
111 96
+
+
+
+
+
+
TABLE IV INTRAMOLECULAR DISTANCES FOR [Co(trenen)Na](NOa)2.HzO D i s t a n c e s w i t h i n [ C a ( t r e n e n ) N3]*' D i s t a n c e (A)
cation D i s t a n c e (A)
I .957(sj
1.510(9)
1.954(5)
1.509(9)
!.992(5)
1.499 (8)
1.952(6)
1.536(1O)
1.964 ( 5 )
1.452(8)
1.957 (61
1.483(8)
1.493(71
1. SZO(l0)
1.525 ( 9 )
1.477(9)
1.488(7)
1.209(7)
1.490(8)
1.152(7)
0 ( 1 ) A( 9 ) 4 ( 2 )
1 2 0 . 6 (5)
0(41--N(10)-0(5)
121.0(6)
0(1)---N(9)--0(3)
l20.9(5)
0(4)+(13)-0(6)
120.3(6)
@(2)---N(9)--0(3)
ll8.5(5)
0(5)+(13)-0(61
116.7(7)
quirement. If some T bonding occurred between the filled d,, orbitals on the metal and the unfilled antibonding T orbitals of the azide ion, maximum orbital overlap would be obtained for an eclipsed configuration. Eclipsing of the azide ion with the co-T\i(5) bond in the present structure involves less steric interaction than eclipsing with any of the other three Co-N bonds. However, more structural data are needed to establish this bonding requirement with certainty. The five-membered chelate rings subtend less than 90" angles a t the metal ion (mean value 86.1 (1)'). These angular distortions mean that the coordination geometry cannot be strictly octahedral. Deviations of the ligating atoms and the metal ion from their mean coordination planes are given in Table VI. TABLE VI LEAST-SQUARES PLANES (a) E q u s t i o n i of p l a n e s AX
where X = ax, Atom included i n plane
BY
i
CZ + D = 0
- -
Plane No.
Z = cz. A
B
C
D
1
0.9583
0.2783
-0.0654
-0.8846
2
0,0059
-0.2167
-0.9762
10.3331
Co, N ( 1 ) , N ( 2 1 , N(31, N(51
3
-0,3003
0.9272
-0,2240
-0.5566
NU),
anions
(b) 1.238(71
I
Y = by,
N ( 4 ) , N ( 5 ) , N(61
Co, N U ) , N ( 4 ) , N ( 3 ) , N(61 to,
D i s t a n c e s w i t h i n NO3-
anions
122
Symmetry transformations: (i) - x , 1 - y , z; (ii) 1 - x , - z; (iv) - x , - z ; (iii) 1 - x , - l / * y, y , '/z - z; (v) x , -1 y , z; (vi) - x , '/z y , '/z - z; (vii) x , 1 y , z; (viii) x , '/P - y, '/z z; (ix) x , '/z - y , - l / * z; ( x ) 1 - x , 1 - y, 1 - 2.
N(91--0(1)
86.7(2) 94.0(21
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102
+
108.5 ( 5 )
107.7 ( 5 )
112
+ y,
107.7(5)
93.5(2)
90
0(6)....N(3)i!-C0iv
a
111.9(5)
87.3(2)
. vi O(3). ...N(ll -
O(5)....N(3)i?-C(4)iX
0(l)....N(5)Vi-Co
1!1.0(5)
d (4)
!l0.5(3)
106
O(2).
~ ( 2 ) 4 ( 2 ) 4 ( 5 )
4
122
109
.
87.0(2)
)
I..
0(6).,..N13)iv-C(4)iv
O ( 2 ) . , .N(4)
111.1(5)
Angle ( d e g . )
O(7)
N(l),,.,O(3)
c(2)4(2)-43)
2.99
0(6)....H-N(3)iv
,
84.7 (2)
2.95
0(2)....H-N(4)vii
O(!).
109.1(4)
N(2)--Co--N(3)
85.6 (2)
O(S)....H-N(3)ix
N(5)- H . . . . O ( l ) i v
Ce-N(2)-C(Sl
2.90
O(3).
...O(3)'
L(!)-H.
86.9(2)
N( 2
.. . H - N ( l l v i O ( 3 ) . . . . H - N(1)""
. . 0 ( 3 ) iv
N (1I - - C a - N [ 2 )
3.16
0(7),...H-C(6)ii
C(6)-H..~.0(7)iii
N( 1 ) - H . .
3.01
0(6)....H-0(7)i
Angle (dcg.)
Atoms
A n g i e (deg.1
Atoms
2.94
0(5)....H-0(7)
..0(6)i
0(7)-H..
A n g l e s w i t h i n [Co(rrenen)N3I2+ c a t i o n
d(X.. ..Y) A
Y....H-X
Atoms
N(101---0(41
D i s t a n c e s of atoms from p l a n e s
1 . 2 3 7 (8)
N(9)2(21
1.257 ( 6 )
N(lO)--O(Sl
1.242(7)
N(g)-JJ(Jl
1.252(7)
N(10)4(6)
1.255 (7)
Atoms
CO
azido group is coplanar with the metal ion and three other ligating nitrogen atoms. In the present structure the least sterically hindered orientation for the azido group would be midway between N ( l ) and N(5) rather than eclipsing the Co-N(5) bond. This feature of coordinated azide might be explained by a bonding re-
D e v i a t i o n s (A) from Plane 1
N(1)
-0.06
Plane 3
0.00
0.01
-0.02
-0.13
0.11
0.09
N(21 N(3)
0.09
N(4)
-0.06
0.11
0.02 -0.02
N(5)
N(61
Plane 2
-0.07
0.02
-0.11
1788 Inorganic Chemistry, Vol. 10, N o . 8,1971
Conformations of the Chelate Rings.-Figure 3 gives a perspective view of the chelate ring conformations and indicates the chirality of each puckered fivemembered ring for that enantiomer. The chelate ring conformations are determined primarily by the configurations at the secondary nitrogen N(4) and the tertiary nitrogen N(2). The deviations of chelate ring carbon atoms from their respective N-Co-N planes and the dihedral angles about the C-C bonds are as follows: C(1), 0.07 A ; C(2), -0.56 A; 47.0'; C(3), -0.75 A; C(4), -0.18 A, 43.8'; C(5), 0.13 A ; C(6), 0.64 A, 38.5'; C(7), 0.51 A ; C(8), -0.11 A, 45.4'. Clearly, the puckering of the chelate rings in all instances is very unsymmetrical. The small torsion angle (38.5") about the C(5)-C(6) bond compares with the value (37.0') found for the central chelate ring of trien in C0(trien)ClOH2~+.~ This is not surprising since in the present structure the ligand can be considered as p-trien with an aminoethyl substituent a t the "angular" nitrogen atom, N(2). Chemical Significance of This Structure. -This structural analysis has revealed a new and interesting bifurcated quinquedentate ligand, 4-(2-aminoethyl)-1,4,7,lO-tetraazadecane (trenen). There are three other possible modes of coordination of this ligand about cobalt(II1) and these are shown in Figure 4. Two of
IANMAXWELL
the possibility of a a-stabilized five-coordinate intermediate proposed for the base hydrolysis of these types of complexes.'? It was shown12for the chloro complex that the base hydrolysis reaction path occurred with full retention of configuration. This result eliminated the possibility of forming a symmetrical five-coordinate intermediate in this system (see Figure 4). Retention is not too surprising since a symmetrical intermediate would involve conformational strain introduced by the eclipsing of all the protons for two coupled five-menibered chelate rings (Figure 5 ) .
I
Figure 5 .
Figure 4
these isomers are diastereoisomers (Figure 4a, b) differing only in the configuration a t a "planar" asymmetric secondary N atom. Therefore, these two isomers are potentially interconvertible by inversion a t this secondary N center. Two more Co(trenen)N32+ isomers have been prepared and separated' on an ion-exchange column but they have not yet been isolated and chemically characterized. As mentioned earlier, apart from the chelate ring conformations, the only source of asymmetry in the present complex, s y m - C ~ ( t r e n e n ) N ~is~ +the asymmetric secondary N center, N(4) (Figure 3). Further, this site of asymmetry is trans to the substituent group. Hence this complex is particularly interesting from a kinetic and mechanistic viewpoint since removal of a proton from this secondary N center, by hydroxide ion, allows the complex to racemize and hydrolyze. Also this center will be the first to deprotonate since the proton is more acidic than any other N-H proton on the ligand by a factor of lo5. The rates and rate laws for base hydrolysis of a series of optically active sym-Co(trenen)X2+(where X - = C1-, N3-) complexes were obtained.12 These studies were carried out to examine the S N ~ C B mechanism and (12) D. A. Buckingham, P. A . Marzilli, and A . M . Sargeson, Inoig. Chem., 8, 1595 (1969).
Another interesting feature of the structure is that inversion at the secondary i i center, h-(4), must be synchronous with conformational interchange of the adjacent coupled chelate rings, in contrast to inversion in Co(NH3)&Ieen3+ (hleen = N-niethylethylenediamine) where conformational interchange could precede or antecede the process. The synchronous conformational interchange is reflected in a higher retention ratio, Khex/kinv, in synz-Co(trenen)NS2+ (2.3 X lo6) than in Co(NH3)Meen8T(1.2 X l O 5 ) ) . I 4 Acknowledgments.-The author wishes to thank Dr. P. A. Llarzilli for crystals used in this study and also Drs. A. M. Sargeson and D. A. Buckingham for their encouragement throughout this work. The calculations were carried out on the CDC 3200/3600 computers of the CSIRO Divisions of Computing Research in Sydney and Canberra and also on an I B M 360/50 computer a t the Computing Center, Australian National University. Computer programs used were the same as those described in a previous p ~ b l i c a t i o n . ~ The author is very grateful to Dr. H. C. Freeman for the use of his diffractometer and for kindly reading the manuscript and also to Dr. M. Sterns for the use of her singlecrystal X-ray camera facilities. The diffraction data were recorded on an automated diffractometer operated under Grant 65/15552 from the Australian Research Grants Committee. (13) R . G. Pearson and F. Basolo, J . Ameu. Ckem. Soc., 78, 4878 (1956). (14) D. A . Buckingham, L. G. Marzilli, and A. hl. Sargeson, i b i d . , 89, 825 (1967).
