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Structural aspects of a macrocyclic metal complex containing a copper(II) ion with unusual spectral and kinetic properties
INORG. NUCL. CHEM. LETTERS Vol.16, pp. 23-26 Pergamon Press Ltd. 1980. Printed in Great Britain
STRUCTURAL ASPECTS OF A MACROCYCLICMETAL COMPLEX CONTAINING A COPPER(II) ION WITH UNUSUAL SPECTRAL AND KINETIC PROPERTIES Richard E. DeSimone, E l l i o t t
L. Blinn* and Kenneth F. Mucker
Department of Chemistry Wayne State University D e t r o i t , Michigan 48202 *Departments of Chemistry and Physics Bowling Green State University Bowling Green, Ohio
43403
(Received 22 August 1979) 1,4,7,10-tetrabenzyl-l,4,7,10-tetraazacyclododecane - hereafter abbreviated tb[12]aneN 4 - c o p p e r ( l l ) complexes have several i n t e r e s t i n g properties.
Despite the fact
that there is no unsaturation in the c y c l i c portion of the ligand, these complexes e x h i b i t unusually high molar e x t i n c t i o n c o e f f i c i e n t s in the v i s i b l e and near infrared portion of the e l e c t r o n i c spectrum (1).
Such a phenomenon is c h a r a c t e r i s t i c of the much studied
Type I copper proteins (2).
Also the c o p p e r ( l l ) complexes of tb[12]aneN 4 are observed
to decompose at a much slower rate than the analogous n i c k e l ( l l ) complexes contrary to usual order of s t a b i l i t y
(3).
Based on the k i n e t i c data and e l e c t r o n i c spectral data i t
was proposed that the c o n f i g r a t i o n of the macrocycle was less folded in the c o p p e r ( l l ) complexes than in the n i c k e l ( l l ) geometries were found.
complexes, where cis-octahedral and t r i g o n a l bipyramidal
The structure of [Cu(tb[12]aneN4)Cl]NO3 was undertaken to advance
our understanding of structure/behavior r e l a t i o n s in metal complexes of this sort. Experimental The compound, [Cu(tb[12]aneN4)Cl]NO3 was prepared by dissolving deep blue Cu(tb[12]aneN4)(N03) 2 ( I ) in H20 and then adding d i l u t e HCI.
A l i g h t blue p r e c i p i t a t e
resulted and t h i s was r e - c r y s t a l l i z e d from ethanol to give well-formed cyrstals.
Three-
dimensional x-ray data was c o l l e c te d on a Syntex P1 automated d i f f r a c t o m e t e r by procedures previously described (4).
The complex c r y s t a l l i z e s in the monoclinic spaceogroup P21/c o
o
with four formula u n i t in a u n i t c e l l of dimensions a = 20.578A, b = II.476A, c = 14.920A, o
= 93.03 ° and a c e l l volume of 3518A3. in the refinement.
A t o t a l of 3136 data with F2> 2.5 a(F 2) were used
The current conventional R1 = .083 and R2 = .115. Results and Discussion
The complex cation has the structure shown in the Figure I.
The coordination
geometry about the c o p p e r ( l l ) ion is that of a square pyramid, with the copper displaced o
by 0.55A above the basal plane defined by the 4 nitrogen atoms. coordination s i t e on the c o p p e r ( l l ) ion is vacant. 23
The s i x t h , or lower ax ia l
When one considers the conformation
24
Structural
Aspects of a Macrocyclic
of the 12-membered ring, this is not surprising.
Metal Complex
The ring portion of the ligand (ie,
the -CH2-groups) is bent back away from the plane of the nitrogen atoms in a direction opposite to that of the copper(II) ion.
One might envision this as forming somewhat of a
hydrophobic pocket which e f f e c t i v e l y r e s t r i c t s access to the lower coordination site of the copper(II) ion.
The four benzyl groups attached to the ring nitrogens are directed
away from the 12-membered ring with the -CH2-(benzyl) somewhat "above" the copper(II) ion and the C6H5-(benzyl ) in a plane roughly parallel to the Cu-N bonds.
\X \\)
),
ii
"~
~i ¸
, J
( Jl "~'I
t
\
.' / ~
i
j)~
FIG. I . A View of the Monomeric Unit _FCu(tbFl2laneN4)ClINO _ . _ _ _ 3
The n i t r a t e group is not coordinated to the c o p p e r ( l l ) .
The complex
[Cu(tb[12]aneN4)(NO3)]N03 is b e l i e v e d to contain both i o n i c and monodentate coordinated nitrate,
p r i m a r i l y on the basis of i n f r a r e d evidence ( I ) .
The 1480 cm-I peak observed in
the s t a r t i n g m a t e r i a l , and assigned to monodentate n i t r a t e ,
is missing in the compound
[Cu(tbLl2]aneN4)Cl](N03). Copper-nitrogen bond distances, which average 2.066A (Table I) are r e l a t i v e l y s i m i l a r to those found in o t h e r c o p p e r - t e r t i a r y amine complexes (5-7).
However, the
TABLE I Selected Bond Distances (A) Cu-CI
2.37
N-O (anion) a
1.15
Cu-Na
2.07
C-N (benzyl) a
1.49
C-N ( r i n g ) a
1.51
C-C (benzyl) a
1.51
C-C ( r i n g ) a
1.53
N-N (adj) a
2.81
a)
average values
Structural Aspects of a Macrocyclic Metal Complex
25
o
apical Cu-CI bond distance is shorter than expected at 2.367A. The axial Cu-CI bond in o
o
the layered CuCI2 structure is 2.95A, in octahedral CsCuCl3 is 2.65A, (8) in chloro-(2,7,12-trimethyl-3,7,11,17-tetraazabicyclo[ll,3,1]heptadeca-l(17), o
2,11,13-pentaene)copper(II)nitrate dihydrate is 2.50A (9) and in tetrachlorobis-2[(5-amino4-carboxamidinium)[l,2,3]triazole])copper(II)homohydrate the apical chloro group is 2.962A from the copper (lO).
Nonapical Cu-Cl distances are usually shorter than the apical Cu-Cl
bond distances l i s t e d here. Another interesting structural feature of this complex is the unusually large displacement of the copper(II) from the least squares plane of the four nitrogens.
The o
observed value of 0.55A is considerably greater than the typical values of 0.2-0.3A encountered in most distorted Cu(II) complexes ( l l ) .
One similar system, reported by
Anderson and Marshall (12) is the Cu(cyclops)NCO (cyclops = d i f l u o r o - 3 , 3 ' - ( t r i m e t h y l enedinitrolo)bis(2-butanone oximato) borate) complex where the displacement of the Cu(II) is 0.58A.
As in [Cu(tb[12]aneN4)Cl]NO3 this large displacement is accompanied
by a r e l a t i v e l y short distance to the atom in the apical position.
Presumably
these shorter axial bonds are also stronger than are t y p i c a l l y found in copper(II) complexes. There are several surprising similaries between the tb[12]aneN 4 and cyclops complexes of copper(II).
Besides the similar large displacement of the copper from the nitrogen
plane and the short copper to apical donor atom bond distances, similar bond angles involving the copper atom were observed. Both complexes have approximately an apical donor to Cu to N bond angle approaching the tetrahedral angle and the inplane N-C-N bond angle are both about 86° (Table I I ) . TABLE I I Selected Bond Angles CI-Cu-Nl
I08.46
NI-CU-N3
148.49
CI-Cu-N2
I06.31
NI-CU-N4
85.71
CI-Cu-N3
I03.05
N2-Cu-N3
85.77
CI-Cu-N4
I05.33
N2-Cu-N4
148.32
NI-CU-N2
85.68
N3-Cu-N4
85.84
The only other copper(ll) complex containing a 12-membered cyclic tetradentate for which the crystal structure has been determined is the copper chloride complex of 1,4,7,10 tetraoxacyclododecane (13).
The geometry of this complex is that of an
elongated and distorted octahedron with the chlorine atoms occupying cis sites. Macrocycles with saturated rings display considerably more f l e x i b i l i t y than those containing various degrees of saturation.
Consequently, even a 12-membered ring is able
to conform i t s e l f to metal coordination without inducing undue strain into the metal coordination sphere.
In the [Cu(tb[12]aneN4)Cl] + ion, coordination is achieved at the
expense of pushing the metal ion out of the equatorial N4 plane, with whatever concomitant decrease in equatorial bond strength may result. L i t t l e evidence of any other ring induced strain in the copper(II) coordination sphere is apparent. One must conclude that the unusual spectral properties of the LCu(tb[12]aneN4)Cl]NO3 complex are most l i k e l y related
26
Structural Aspects of a Macrocyclic Metal Complex
to the pyramidal geometry and perhaps stronger than normal a x i a l Cu-CI bond, rather than to any extraordinary s t r a i n and/or deformation from a regular coordination geometry. unusual k i n e t i c s t a b i l i t y
of t h i s complex may also be due to the same factors.
The
One might
speculate that macrocycle r e - o r i e n t a t i o n or d i s s o c i a t i o n may be i n h i b i t e d by d i f f i c u l t y
in
d i s s o c i a t i n g the apical chloride. Acknowlegement Acknowlegement is made to the donors of the Petroleum Research Fund administered by the American Chemical Society, f o r p a r t i a l support of t h i s research. acknowledged f o r preparing the complex.
Harry Mahoney is
Milton Glick is acknowledged for assistance. References
I.
M. C.Styka, R. C Smierciak, E. L. B l i n n , R. E. DeSimone and J. V. Passariello, Inorg.
2.
J. A. Fee, Struct. Bonding ( B e r l i n ) , 23, 1 (1975).
Chem., 17, 82 (1978). 3.
J. V. Passariello and E. L. B l i n n , 170th Meeting of ACS in Chicago, 1975.
4.
R. E. DeSimone and M. D. Glick, Inorg. Chem., 17, 3574 (1978).
5.
E. D. Estes, W. E. Estes, W. E. H a t f i e l d and D. J. Hodgson, Inorg. Chem. 14, 106 (1975)
6.
E. D. Estes, and D. J. Hodgson, Inorg. Chem., 14, 334 (1975).
7.
E. D. Estes, W. E. H a t f i e l d and D. J. Hodgson, Inorg. Chem., 13, 1654 (1974).
8.
F. A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry", 3rd ed, Interscience,
9.
M. R. Cairo, L. R. Nassimbeni and P. R. Woolley, Acta Cryst B., 31, 1334 (1975).
N. Y., N.Y., 1972.
I0.
L. G. P u r n e l l , J. C. Shepherd and D. J. Hodgson, J. Am. Chem. Soc., 97, 2376 (1975).
II. 12.
J. L. Templeton, R. C. Jacobson and R. E. McCarley, Inorg. Chem., 17, 3320 (1978).
13.
F. P. van Remoortee, F. P. Boer and E. C. Steiner, Acta Cryst B, 31, 1420 (1975).
O. P. Anderson and J. C. Marshall, Inorg. Chem., 17, 1258 (1978).
STRUCTURAL ASPECTS OF A MACROCYCLICMETAL COMPLEX CONTAINING A COPPER(II) ION WITH UNUSUAL SPECTRAL AND KINETIC PROPERTIES Richard E. DeSimone, E l l i o t t
L. Blinn* and Kenneth F. Mucker
Department of Chemistry Wayne State University D e t r o i t , Michigan 48202 *Departments of Chemistry and Physics Bowling Green State University Bowling Green, Ohio
43403
(Received 22 August 1979) 1,4,7,10-tetrabenzyl-l,4,7,10-tetraazacyclododecane - hereafter abbreviated tb[12]aneN 4 - c o p p e r ( l l ) complexes have several i n t e r e s t i n g properties.
Despite the fact
that there is no unsaturation in the c y c l i c portion of the ligand, these complexes e x h i b i t unusually high molar e x t i n c t i o n c o e f f i c i e n t s in the v i s i b l e and near infrared portion of the e l e c t r o n i c spectrum (1).
Such a phenomenon is c h a r a c t e r i s t i c of the much studied
Type I copper proteins (2).
Also the c o p p e r ( l l ) complexes of tb[12]aneN 4 are observed
to decompose at a much slower rate than the analogous n i c k e l ( l l ) complexes contrary to usual order of s t a b i l i t y
(3).
Based on the k i n e t i c data and e l e c t r o n i c spectral data i t
was proposed that the c o n f i g r a t i o n of the macrocycle was less folded in the c o p p e r ( l l ) complexes than in the n i c k e l ( l l ) geometries were found.
complexes, where cis-octahedral and t r i g o n a l bipyramidal
The structure of [Cu(tb[12]aneN4)Cl]NO3 was undertaken to advance
our understanding of structure/behavior r e l a t i o n s in metal complexes of this sort. Experimental The compound, [Cu(tb[12]aneN4)Cl]NO3 was prepared by dissolving deep blue Cu(tb[12]aneN4)(N03) 2 ( I ) in H20 and then adding d i l u t e HCI.
A l i g h t blue p r e c i p i t a t e
resulted and t h i s was r e - c r y s t a l l i z e d from ethanol to give well-formed cyrstals.
Three-
dimensional x-ray data was c o l l e c te d on a Syntex P1 automated d i f f r a c t o m e t e r by procedures previously described (4).
The complex c r y s t a l l i z e s in the monoclinic spaceogroup P21/c o
o
with four formula u n i t in a u n i t c e l l of dimensions a = 20.578A, b = II.476A, c = 14.920A, o
= 93.03 ° and a c e l l volume of 3518A3. in the refinement.
A t o t a l of 3136 data with F2> 2.5 a(F 2) were used
The current conventional R1 = .083 and R2 = .115. Results and Discussion
The complex cation has the structure shown in the Figure I.
The coordination
geometry about the c o p p e r ( l l ) ion is that of a square pyramid, with the copper displaced o
by 0.55A above the basal plane defined by the 4 nitrogen atoms. coordination s i t e on the c o p p e r ( l l ) ion is vacant. 23
The s i x t h , or lower ax ia l
When one considers the conformation
24
Structural
Aspects of a Macrocyclic
of the 12-membered ring, this is not surprising.
Metal Complex
The ring portion of the ligand (ie,
the -CH2-groups) is bent back away from the plane of the nitrogen atoms in a direction opposite to that of the copper(II) ion.
One might envision this as forming somewhat of a
hydrophobic pocket which e f f e c t i v e l y r e s t r i c t s access to the lower coordination site of the copper(II) ion.
The four benzyl groups attached to the ring nitrogens are directed
away from the 12-membered ring with the -CH2-(benzyl) somewhat "above" the copper(II) ion and the C6H5-(benzyl ) in a plane roughly parallel to the Cu-N bonds.
\X \\)
),
ii
"~
~i ¸
, J
( Jl "~'I
t
\
.' / ~
i
j)~
FIG. I . A View of the Monomeric Unit _FCu(tbFl2laneN4)ClINO _ . _ _ _ 3
The n i t r a t e group is not coordinated to the c o p p e r ( l l ) .
The complex
[Cu(tb[12]aneN4)(NO3)]N03 is b e l i e v e d to contain both i o n i c and monodentate coordinated nitrate,
p r i m a r i l y on the basis of i n f r a r e d evidence ( I ) .
The 1480 cm-I peak observed in
the s t a r t i n g m a t e r i a l , and assigned to monodentate n i t r a t e ,
is missing in the compound
[Cu(tbLl2]aneN4)Cl](N03). Copper-nitrogen bond distances, which average 2.066A (Table I) are r e l a t i v e l y s i m i l a r to those found in o t h e r c o p p e r - t e r t i a r y amine complexes (5-7).
However, the
TABLE I Selected Bond Distances (A) Cu-CI
2.37
N-O (anion) a
1.15
Cu-Na
2.07
C-N (benzyl) a
1.49
C-N ( r i n g ) a
1.51
C-C (benzyl) a
1.51
C-C ( r i n g ) a
1.53
N-N (adj) a
2.81
a)
average values
Structural Aspects of a Macrocyclic Metal Complex
25
o
apical Cu-CI bond distance is shorter than expected at 2.367A. The axial Cu-CI bond in o
o
the layered CuCI2 structure is 2.95A, in octahedral CsCuCl3 is 2.65A, (8) in chloro-(2,7,12-trimethyl-3,7,11,17-tetraazabicyclo[ll,3,1]heptadeca-l(17), o
2,11,13-pentaene)copper(II)nitrate dihydrate is 2.50A (9) and in tetrachlorobis-2[(5-amino4-carboxamidinium)[l,2,3]triazole])copper(II)homohydrate the apical chloro group is 2.962A from the copper (lO).
Nonapical Cu-Cl distances are usually shorter than the apical Cu-Cl
bond distances l i s t e d here. Another interesting structural feature of this complex is the unusually large displacement of the copper(II) from the least squares plane of the four nitrogens.
The o
observed value of 0.55A is considerably greater than the typical values of 0.2-0.3A encountered in most distorted Cu(II) complexes ( l l ) .
One similar system, reported by
Anderson and Marshall (12) is the Cu(cyclops)NCO (cyclops = d i f l u o r o - 3 , 3 ' - ( t r i m e t h y l enedinitrolo)bis(2-butanone oximato) borate) complex where the displacement of the Cu(II) is 0.58A.
As in [Cu(tb[12]aneN4)Cl]NO3 this large displacement is accompanied
by a r e l a t i v e l y short distance to the atom in the apical position.
Presumably
these shorter axial bonds are also stronger than are t y p i c a l l y found in copper(II) complexes. There are several surprising similaries between the tb[12]aneN 4 and cyclops complexes of copper(II).
Besides the similar large displacement of the copper from the nitrogen
plane and the short copper to apical donor atom bond distances, similar bond angles involving the copper atom were observed. Both complexes have approximately an apical donor to Cu to N bond angle approaching the tetrahedral angle and the inplane N-C-N bond angle are both about 86° (Table I I ) . TABLE I I Selected Bond Angles CI-Cu-Nl
I08.46
NI-CU-N3
148.49
CI-Cu-N2
I06.31
NI-CU-N4
85.71
CI-Cu-N3
I03.05
N2-Cu-N3
85.77
CI-Cu-N4
I05.33
N2-Cu-N4
148.32
NI-CU-N2
85.68
N3-Cu-N4
85.84
The only other copper(ll) complex containing a 12-membered cyclic tetradentate for which the crystal structure has been determined is the copper chloride complex of 1,4,7,10 tetraoxacyclododecane (13).
The geometry of this complex is that of an
elongated and distorted octahedron with the chlorine atoms occupying cis sites. Macrocycles with saturated rings display considerably more f l e x i b i l i t y than those containing various degrees of saturation.
Consequently, even a 12-membered ring is able
to conform i t s e l f to metal coordination without inducing undue strain into the metal coordination sphere.
In the [Cu(tb[12]aneN4)Cl] + ion, coordination is achieved at the
expense of pushing the metal ion out of the equatorial N4 plane, with whatever concomitant decrease in equatorial bond strength may result. L i t t l e evidence of any other ring induced strain in the copper(II) coordination sphere is apparent. One must conclude that the unusual spectral properties of the LCu(tb[12]aneN4)Cl]NO3 complex are most l i k e l y related
26
Structural Aspects of a Macrocyclic Metal Complex
to the pyramidal geometry and perhaps stronger than normal a x i a l Cu-CI bond, rather than to any extraordinary s t r a i n and/or deformation from a regular coordination geometry. unusual k i n e t i c s t a b i l i t y
of t h i s complex may also be due to the same factors.
The
One might
speculate that macrocycle r e - o r i e n t a t i o n or d i s s o c i a t i o n may be i n h i b i t e d by d i f f i c u l t y
in
d i s s o c i a t i n g the apical chloride. Acknowlegement Acknowlegement is made to the donors of the Petroleum Research Fund administered by the American Chemical Society, f o r p a r t i a l support of t h i s research. acknowledged f o r preparing the complex.
Harry Mahoney is
Milton Glick is acknowledged for assistance. References
I.
M. C.Styka, R. C Smierciak, E. L. B l i n n , R. E. DeSimone and J. V. Passariello, Inorg.
2.
J. A. Fee, Struct. Bonding ( B e r l i n ) , 23, 1 (1975).
Chem., 17, 82 (1978). 3.
J. V. Passariello and E. L. B l i n n , 170th Meeting of ACS in Chicago, 1975.
4.
R. E. DeSimone and M. D. Glick, Inorg. Chem., 17, 3574 (1978).
5.
E. D. Estes, W. E. Estes, W. E. H a t f i e l d and D. J. Hodgson, Inorg. Chem. 14, 106 (1975)
6.
E. D. Estes, and D. J. Hodgson, Inorg. Chem., 14, 334 (1975).
7.
E. D. Estes, W. E. H a t f i e l d and D. J. Hodgson, Inorg. Chem., 13, 1654 (1974).
8.
F. A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry", 3rd ed, Interscience,
9.
M. R. Cairo, L. R. Nassimbeni and P. R. Woolley, Acta Cryst B., 31, 1334 (1975).
N. Y., N.Y., 1972.
I0.
L. G. P u r n e l l , J. C. Shepherd and D. J. Hodgson, J. Am. Chem. Soc., 97, 2376 (1975).
II. 12.
J. L. Templeton, R. C. Jacobson and R. E. McCarley, Inorg. Chem., 17, 3320 (1978).
13.
F. P. van Remoortee, F. P. Boer and E. C. Steiner, Acta Cryst B, 31, 1420 (1975).
O. P. Anderson and J. C. Marshall, Inorg. Chem., 17, 1258 (1978).