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Pendent arm macrocyclic complexes: crystal structures of AI(TCTA) and In(TS-TACN)
Polyhedron Vol. 12, No. I, pp. I-5, 1993 Printed in Great Britain
0
0277-5387/93 $6.00+.00 1993 Pergamon Press Ltd
PENDENT ARM MACROCYCLIC COMPLEXES : CRYSTAL STRUCTURES OF Al(TCTA) AND In(TS-TACN) URSULA BOSSEK, DIETER
HANKE and KARL WIEGHARDT*
Lehrstuhl fur Anorganische Chemie I, Ruhr-Universitat,
D-4630 Bochum, Germany
and BERNHARD NUBER
Anorganisch-Chemisches
Institut der Universitat, D-6900 Heidelberg, Germany
(Received 2 June 1992 ; accepted 10 September
1992)
Abstract-Complexes of A13+ and In3+ containing the pendent arm macrocycles 1,4,7tris(acetato)-1,4,7-triazacyclononane (TCTA) and 1,4,7-tris(2-mercaptoethyl)-1,4,7-triazacyclononane (TS-TACN), respectively, have been synthesized and their crystal structures determined. Al(TCTA) contains an octahedral&c-N303 donor set, whereas In(TS-TACN) has an octahedral&-N3S3 donor set. Average Al-G and In-S distances are 1.846 and 2.397 A, respectively.
from these studies that Al(TCTA) is even more stable. Fanwick et a1.,5 on the other hand, have introduced a macrocycle with a 1,4,7-triazacyclononane backbone and three 2-mercaptoethyl pendent arms and have reported the structure of Ga(TS-TACN). In 1982 we reported the synthesis of Al(TCTA), ”
The coordination chemistry of trivalent group 13 metal ions with trianionic pendent-arm macrocyclic ligands (Scheme I) has attracted considerable interest in recent years as potential diagnostic radiopharmaceuticals (Ga, In).‘** Their use in vivo in nuclear medicine requires kinetic inertness and, in addition, it appears to be desirable that such complexes are electroneutral, have a low molecular weight and are lipophilic in order to cross the blood-brain barrier. Aluminium complexes of this type are also of interest due to the possible involvement of this element in Alzheimer’s disease3 and removal of A13+ from the body. Parker et al. and Kaden et al. have recently published the synthesis and crystal structures of Ga(TCTA),4*5 In(RMeTCTA),6 In(TCTA-H)C17 and InL’*8 and tested their utility as radiopharmaceuticals. Clarke and Martell have established that Ga’I’ and In”’ bind very strongly to TCTA and noted in accord with Hancock et al.‘s”*’ ’ molecular mechanics calculations that this ligand preferentially binds to small metal ions. Stability constants (KML= [ML]/[L3-][M3+]) of Ga3+ and In3+ are 1030.g8and 10z6.‘, respectively. It is to be expected
c
0
0
+
0e
09
TCTA
(R)
L’
*Author to whom correspondence should be addressed.
TS - TACN
Scheme I. 1
- MeTCTA
2
U. BOSSEK et al.
which is extremely stable in aqueous solution over a wide range of pH (O-l 3) for many days at ambient temperature. We have now determined the crystal structure of this complex. The structure has been briefly reported previously, I3 Since the quality of our structure determination is better we decided to publish our data. Independently of Moore’s work, 5 we have prepared the neutral complex In(TSTACN), the structure of which we also report here. RESULTS
AND DISCUSSION
Colourless crystals suitable for the X-ray crystallography of Al(TCTA) were obtained from the reaction of an aqueous solution of the hexadentate ligand and AlC13* 6HZ0, as described in ref. 12. Figure 1 shows the structure ; important bond distances and angles are summarized in Table 1. Table 2 gives selected bond lengths and angles of the corresponding complexes of Ga”‘, Inn‘ and Fe”‘. As Hancock et al. lo pointed out there are two possible arrangements for the coordinated acetate groups on the pseudo-octahedral complexes of TCTA. The bound base fragment 1,4,7-t& azacyclononane is chiral. For a given arrangement of the base fragment, (ALA)or (666) conformation
0141
Fig. 1. The structure of Al(TCTA).
of the five-membered M-N-C-C-& chelate rings, the acetate goups may be oriented in a clockwise or anticlockwise fashion (A, A configuration). The change from type I [A(&Ll), A(&%) enantiomers] to type II [A(W), A(Jnn) enantiomers]59g is a consequence of the increasing M-N bond distance, which forces the metal ion up out of the nine-mem-
Table 1. Selected bond distances (A) and angles (“) in Al(TCTA) and In(TSTACN) Al(TCTA) Al-N( 1) Al-N(2) Al-N( 3) N( 1)---A&N(2) N(l)-Al-N(3) N(2)-Al-N(3) N(l)-Al-O(l) N(2)-A&O(2) N(3)-Al-Q( 1) N(3)-A&O(5) O(3)-Al-O(S) In(TS-TACN) In-S( 1) In-S(2) In-S( 3) S(l)-in---S(2) S(l)-In-S(3) S(l)-In-N(l) S(l)-In-N(2) S(I)-In-N(3) N( I)-In-N(2) N( l)-In-N(3) N(2)-In-N(3)
2.065(3) 2.054(3) 2.051(2) 84.4(1) 84.5(l) 84.4(1) 83.7(l) 96.1(l) 168.0(l) 84.0(1) 95.9(1)
2.499(1) 2.515(l) 2.518(l) 102.6(l) 106.4(1) 156.2(l) 99.0(1) 81.7(l) 74.4(l) 74.5(l) 73.8(1)
Al-O( 1) Al--a(3) A1--0(5) N( l)-A1-0(3) N(2)-A&O(3) N(3)-A1-0(3) 0(1)-A&O(3) N(l)-A-(5) N(2)-Al-O(5) O(l)-Al--o(S)
In-N( 1) In-N( 2) In-N(3) S(2)-in-S(3) S(2)-In-N( 1) S(2)-In-N(2) S(2j-In-N(3) S(3)-In-N( 1) S(3)-In-N(2) S(3)--In-N(3)
1.851(2) 1.846(2) 1.840(2) 168.1(l) 84.0(1) 96.8(1) 95.1(l) 96.0(1) 168.3(l) 95.6(l)
2.379(2) 2.403(2) 2.408(3) 104.5(l) 81.3(l) 155.6(l) 98.2(l) 95.0(l) 79.8(l) 153.3(l)
Pendent arm macrocyclic complexes Table 2. Comparison av. M-G Complex
(A)
Al(TCTA) Ga(TCTA) In( R-MeTCTA) InL’ Fe(TCTA) In(TCTA-H)Cl
1.846 1.933 2.096 2.16-2.20 1.962 2.284, 2.424 2.116
Ga(TS-TACN) In(TS-TACN)
of structural data of complexes
av. M-S (A)
2.339 2.511
av. M-N (A) 2.057 2.097 2.261 2.36 2.181 2.332, 2.288 2.331 2.208 2.397
C.N.”
0 (“)’
Ref.
6 6 6 7 6 7
25.5 23.8 10.4 12.6 -
This work 4, 11 5 7 12 6
6 6
24.8 23
11 This work
Ligand abbreviations are as in Scheme I. “C.N. = coordination number. bTwist angle as defined in the text.
bered 1,4,7-triazacyclononane ring which causes a strain on the M-O bond. This tension may then be somewhat relieved by switching to the type II structure.“’ The twist angle 8 is defined as shown below.
It is 30” for a perfect octahedron and 0” for a trigonal prism. It is clearly seen from the compilation of 8 values in Table 2 that Al(TCTA) and Ga(TCTA) have slightly distorted octahedral geometry, whereas for In((R)-MeTCTA) a trigonal prism prevails. This switch from an octahedral to a trigonal prismatic polyhedron relieves the above mentioned strain which is imposed on the ligand by increasing M-N and M-O distances. It is interesting that Ga(TCTA) is octahedral whereas Fe(TCTA) is trigonal prismatic, although the eflective ionic radii of six-coordinate Ga3+ of 0.76 8, and of high-spin Fe3+ of 0.785 A are actually quite similar. I4 It appears that the configurational switch is triggered within a narrow range of M-N and M-O distances and does not occur gradually. Not surprisingly, in Al(TCTA) the shortest M-N and M-G distances are observed as compared to those in Ga(TCTA)4J and In((R)MeTCTA). 6 Consequently, Al(TCTA) and Ga(TCTA) are octahedral (type I), whereas In((R)MeTCTA) is more trigonal prismatic (type II). The
Al-O distance in Al(TCTA) is very short at 1.846(2) A and may be compared with the corresponding distance in [Al(OH&](NOJ3 - 3H20 of 1.877(2) A.” The reaction of InBr, dissolved in a sodium methanolate/methanol mixture with the ligand 1,4,7-tris(2-mercaptoethyl)-1,4,7-triazacyclononane at 20°C produced colourless microcrystals of In(TS-TACN). Single crystals were obtained from a hot aqueous solution upon slow cooling. Figure 2 shows the structure, Table 1 summarizes selected bond distances and angles. The ligand is hexadentate providing a fuc-N3S3 donor set around the indium(II1) metal ion. As Moore et al. have discussed for Ga(TS-TACN) the coordinated ligand TS-TACN has three different sources of chirality. The 1,4,7-triazacyclononane backbone adopts either a (666), or (U&, conformation, the three pendent arms have either (6&Q,, or(U), configuration and, in addition, may adopt (U), or (6&Q conformation in either configuration. In crystals of Ga(TS-TACN) * 2CH2C12 both enantiomeric forms of the neutral complex A(J.U),(&V), and A(&@@.~), are present in the centric unit cell of the space group P2,/n. In(TSTACN) crystallizes in the same space group and the same enantiomers are present [A(U),(&?), and A(~&I),(U.),], despite the fact that the M-N and M-S bond distances increase by 0.189 and 0.172 A, respectively, on going from Ga3+ to In3+. These differences reflect quite accurately the enormous difference of effective ionic radii of 0.18 8, between six-coordinate Ga3+ and In3+. We conclude from these observations that the ligand TS-TACN exhibits more flexibility towards average
U. BOSSEK et al.
Fig. 2. The structure of In(TS-TACN).
binding of small and large metal ions than its counterpart TCTA with three acetate pendent arms. EXPERIMENTAL The compound Al(TCTA) and the ligand 1,4,7tris(2-mercaptoethyl)-1,4,7-triazacyclononane (TSTACN) were synthesized according to published procedures. 5,I2 Synthesis of In(TS-TACN)
Sodium metal (0.15 g) was carefully dissolved in dry ethanol (25 cm3) and InBr, (0.35 g, 1.0 mmol) was added to this solution. To the clear solution the ligand TS-TACN (0.34 g, 1.0 mmol) was added dropwise with stirring at ambient temperature. After 2-3 h a colourless precipitate of In(TSTACN) formed, which was collected by filtration, washed with ethanol and diethylether and air-dried. Needle shaped, colourless crystals suitable for Xray crystallography were obtained from recrystallization from a hot water solution (9YC) which was allowed to slowly cool to 20°C (yield : 0.18 g, 43%). Found: C, 34.4; H, 5.8; N, 9.8; S, 22.6. Calc. for C12H24N3S31n: C, 34.2; H, 5.7; N, 10.0; S, 22.8%. Crystal structure determinations Crystal data. [C i2HI eN306A1], M = 327.27, monoclinic, space group P2,/n, a = 8.803(6),
b = 13.526(9), c = 11.983(6) A, /3 = 105.43(5)“, U = 1375.4 A’ (from 28 values for 25 reflections measured at 15” < 26 < 37”), I = 0.71073 A, T = 298 K, Z = 4, D, = 1.58 g cn- 3, ~(MoK,) = 0.18 nun’. [C12H24N3S31n],A4 = 421.35, monoclinic, space a = 7.292(l), b = 16.807(4), P2 IIn, group c = 13.107(2) A, /? = 93.69(2)“, U = 1603.0 A’ (from 28 values for 25 reflections measured at 22 < 20 < 40”), A = 0.71073 A, T = 298 K, Z = 4, D, = 1.75 g cmp3, ~(Mo-K,) = 1.82 mm-‘. Data processing and structure solution. Intensity data were collected using a Syntex R3 diffractometer, equipped with a graphite monochromator and an MO-K, radiation source (e-scans). Data were corrected for Lorentz and polarization effects in the usual manner and absorption corrections (+scans of seven reflections) were also carried out in both cases. For Al(TCTA) 4500 reflections were measured (28,,, = 60”, h -ll-+8, k O-16, I 0- 16) yielding 2694 with I > 2.50(I) ; for In(TSTACN) 5 144 reflections were measured (28, = k O-20, I O-+18) yielding 3809 60”, h -10-11, with Z 2 2.50(Z). Both structures were solved by Patterson and difference-Fourier methods, and refined by standard least-squares techniques (SHELXTL PLUS program system). The positions of the hydrogen atoms were calculated and included in the refinement with a common isotropic thermal parameter (Vi,, = 0.080 A’) ; all other atoms were refined with anisotropic thermal parameters. The weighting scheme w-i = a’(F) was used throughout. For Al(TCTA) refine-
Pendent arm macrocyclic complexes ment converged with R = 0.049,R, = 0.048and for In(TS-TACN) with R = 0.032,R, = 0.029. Neutral atom scattering factors and anomalous dispersion data were taken from ref. 16. Final difference maps had no chemically significant maxima. Thermal parameters, fractional atom coordinates, listings of observed and calculated structure 8. factors have been deposited with the Editor, from whom copies are available on request. Atom coor9. dinates have also been deposited with the Cambridge Crystallographic Data Centre. 10. 11.
REFERENCES 1. M. E. Raichle, Adu. Chem. Ser. 198 1, 197,419. 2. V. L. Alvarez, M. L. Wen, C. Lee, A. D. Lopes, J. D. Rodwell and T. J. McKearn, Nucl. Med. Biol. 1986, 13, 347. 3. J. J. R. F. da Silva and R. J. P. Williams, The Biological Chemistry of the Elements. Clarendon Press, Oxford (1991). 4. A. S. Craig, D. Parker, H. Adams and N. A. Bailey, J. Chem. Sot., Chem. Commun. 1989, 1793.
12.
13. 14. 15. 16.
5
D. A. Moore, P. E. Fanwick and M. J. Welch, Znorg. Chem. 1990,29,672. R. C. Matthews, D. Parker, G. Ferguson, B. Kaitner, A. Harrison and L. Royle, Polyhedron 1991,10,1951. A. C. Craig, I. M. Helps, D. Parker, H. Adams, N. A. Bailey, M. G. Williams, J. M. A. Smith and G. Ferguson, Polyhedron 1989,8,248 1. A. Riesen, T. A. Kaden, W. Ritter and H. R. Macke, J. Chem. Sot., Chem. Commun. 1989,460. E. T. Clarke and A. E. Martell, Znorg. Chim. Acta 1991,181,273. M. J. van der Merve, J. C. A. Boeyens and R. D. Hancock, Znorg. Chem. 1985,24, 1208. T. W. Duma, F. Marsicano and R. D. Hancock, J. Coord. Chem. 1991,23,221. K. Wieghardt, U. Bossek, P. Chaudhuri, W. Herrmann, B. C. Menke and J. Weiss, Znorg. Chem. 1982, 21,4308. A. Jyo, Y. Kohno, Y. Terazono and S. Kawano, Anal. Sci. 1990, 6, 629. R. D. Shannon, Acta Cryst. 1976, A32, 751. D. Lazar, B. Ribbr and B. Prelesnik, Acta Cryst. 199 1, C47,2282. International Tables for Crystallography, Vol. IV, pp. 99 and 149. Kynoch Press, Birmingham (1974).
0
0277-5387/93 $6.00+.00 1993 Pergamon Press Ltd
PENDENT ARM MACROCYCLIC COMPLEXES : CRYSTAL STRUCTURES OF Al(TCTA) AND In(TS-TACN) URSULA BOSSEK, DIETER
HANKE and KARL WIEGHARDT*
Lehrstuhl fur Anorganische Chemie I, Ruhr-Universitat,
D-4630 Bochum, Germany
and BERNHARD NUBER
Anorganisch-Chemisches
Institut der Universitat, D-6900 Heidelberg, Germany
(Received 2 June 1992 ; accepted 10 September
1992)
Abstract-Complexes of A13+ and In3+ containing the pendent arm macrocycles 1,4,7tris(acetato)-1,4,7-triazacyclononane (TCTA) and 1,4,7-tris(2-mercaptoethyl)-1,4,7-triazacyclononane (TS-TACN), respectively, have been synthesized and their crystal structures determined. Al(TCTA) contains an octahedral&c-N303 donor set, whereas In(TS-TACN) has an octahedral&-N3S3 donor set. Average Al-G and In-S distances are 1.846 and 2.397 A, respectively.
from these studies that Al(TCTA) is even more stable. Fanwick et a1.,5 on the other hand, have introduced a macrocycle with a 1,4,7-triazacyclononane backbone and three 2-mercaptoethyl pendent arms and have reported the structure of Ga(TS-TACN). In 1982 we reported the synthesis of Al(TCTA), ”
The coordination chemistry of trivalent group 13 metal ions with trianionic pendent-arm macrocyclic ligands (Scheme I) has attracted considerable interest in recent years as potential diagnostic radiopharmaceuticals (Ga, In).‘** Their use in vivo in nuclear medicine requires kinetic inertness and, in addition, it appears to be desirable that such complexes are electroneutral, have a low molecular weight and are lipophilic in order to cross the blood-brain barrier. Aluminium complexes of this type are also of interest due to the possible involvement of this element in Alzheimer’s disease3 and removal of A13+ from the body. Parker et al. and Kaden et al. have recently published the synthesis and crystal structures of Ga(TCTA),4*5 In(RMeTCTA),6 In(TCTA-H)C17 and InL’*8 and tested their utility as radiopharmaceuticals. Clarke and Martell have established that Ga’I’ and In”’ bind very strongly to TCTA and noted in accord with Hancock et al.‘s”*’ ’ molecular mechanics calculations that this ligand preferentially binds to small metal ions. Stability constants (KML= [ML]/[L3-][M3+]) of Ga3+ and In3+ are 1030.g8and 10z6.‘, respectively. It is to be expected
c
0
0
+
0e
09
TCTA
(R)
L’
*Author to whom correspondence should be addressed.
TS - TACN
Scheme I. 1
- MeTCTA
2
U. BOSSEK et al.
which is extremely stable in aqueous solution over a wide range of pH (O-l 3) for many days at ambient temperature. We have now determined the crystal structure of this complex. The structure has been briefly reported previously, I3 Since the quality of our structure determination is better we decided to publish our data. Independently of Moore’s work, 5 we have prepared the neutral complex In(TSTACN), the structure of which we also report here. RESULTS
AND DISCUSSION
Colourless crystals suitable for the X-ray crystallography of Al(TCTA) were obtained from the reaction of an aqueous solution of the hexadentate ligand and AlC13* 6HZ0, as described in ref. 12. Figure 1 shows the structure ; important bond distances and angles are summarized in Table 1. Table 2 gives selected bond lengths and angles of the corresponding complexes of Ga”‘, Inn‘ and Fe”‘. As Hancock et al. lo pointed out there are two possible arrangements for the coordinated acetate groups on the pseudo-octahedral complexes of TCTA. The bound base fragment 1,4,7-t& azacyclononane is chiral. For a given arrangement of the base fragment, (ALA)or (666) conformation
0141
Fig. 1. The structure of Al(TCTA).
of the five-membered M-N-C-C-& chelate rings, the acetate goups may be oriented in a clockwise or anticlockwise fashion (A, A configuration). The change from type I [A(&Ll), A(&%) enantiomers] to type II [A(W), A(Jnn) enantiomers]59g is a consequence of the increasing M-N bond distance, which forces the metal ion up out of the nine-mem-
Table 1. Selected bond distances (A) and angles (“) in Al(TCTA) and In(TSTACN) Al(TCTA) Al-N( 1) Al-N(2) Al-N( 3) N( 1)---A&N(2) N(l)-Al-N(3) N(2)-Al-N(3) N(l)-Al-O(l) N(2)-A&O(2) N(3)-Al-Q( 1) N(3)-A&O(5) O(3)-Al-O(S) In(TS-TACN) In-S( 1) In-S(2) In-S( 3) S(l)-in---S(2) S(l)-In-S(3) S(l)-In-N(l) S(l)-In-N(2) S(I)-In-N(3) N( I)-In-N(2) N( l)-In-N(3) N(2)-In-N(3)
2.065(3) 2.054(3) 2.051(2) 84.4(1) 84.5(l) 84.4(1) 83.7(l) 96.1(l) 168.0(l) 84.0(1) 95.9(1)
2.499(1) 2.515(l) 2.518(l) 102.6(l) 106.4(1) 156.2(l) 99.0(1) 81.7(l) 74.4(l) 74.5(l) 73.8(1)
Al-O( 1) Al--a(3) A1--0(5) N( l)-A1-0(3) N(2)-A&O(3) N(3)-A1-0(3) 0(1)-A&O(3) N(l)-A-(5) N(2)-Al-O(5) O(l)-Al--o(S)
In-N( 1) In-N( 2) In-N(3) S(2)-in-S(3) S(2)-In-N( 1) S(2)-In-N(2) S(2j-In-N(3) S(3)-In-N( 1) S(3)-In-N(2) S(3)--In-N(3)
1.851(2) 1.846(2) 1.840(2) 168.1(l) 84.0(1) 96.8(1) 95.1(l) 96.0(1) 168.3(l) 95.6(l)
2.379(2) 2.403(2) 2.408(3) 104.5(l) 81.3(l) 155.6(l) 98.2(l) 95.0(l) 79.8(l) 153.3(l)
Pendent arm macrocyclic complexes Table 2. Comparison av. M-G Complex
(A)
Al(TCTA) Ga(TCTA) In( R-MeTCTA) InL’ Fe(TCTA) In(TCTA-H)Cl
1.846 1.933 2.096 2.16-2.20 1.962 2.284, 2.424 2.116
Ga(TS-TACN) In(TS-TACN)
of structural data of complexes
av. M-S (A)
2.339 2.511
av. M-N (A) 2.057 2.097 2.261 2.36 2.181 2.332, 2.288 2.331 2.208 2.397
C.N.”
0 (“)’
Ref.
6 6 6 7 6 7
25.5 23.8 10.4 12.6 -
This work 4, 11 5 7 12 6
6 6
24.8 23
11 This work
Ligand abbreviations are as in Scheme I. “C.N. = coordination number. bTwist angle as defined in the text.
bered 1,4,7-triazacyclononane ring which causes a strain on the M-O bond. This tension may then be somewhat relieved by switching to the type II structure.“’ The twist angle 8 is defined as shown below.
It is 30” for a perfect octahedron and 0” for a trigonal prism. It is clearly seen from the compilation of 8 values in Table 2 that Al(TCTA) and Ga(TCTA) have slightly distorted octahedral geometry, whereas for In((R)-MeTCTA) a trigonal prism prevails. This switch from an octahedral to a trigonal prismatic polyhedron relieves the above mentioned strain which is imposed on the ligand by increasing M-N and M-O distances. It is interesting that Ga(TCTA) is octahedral whereas Fe(TCTA) is trigonal prismatic, although the eflective ionic radii of six-coordinate Ga3+ of 0.76 8, and of high-spin Fe3+ of 0.785 A are actually quite similar. I4 It appears that the configurational switch is triggered within a narrow range of M-N and M-O distances and does not occur gradually. Not surprisingly, in Al(TCTA) the shortest M-N and M-G distances are observed as compared to those in Ga(TCTA)4J and In((R)MeTCTA). 6 Consequently, Al(TCTA) and Ga(TCTA) are octahedral (type I), whereas In((R)MeTCTA) is more trigonal prismatic (type II). The
Al-O distance in Al(TCTA) is very short at 1.846(2) A and may be compared with the corresponding distance in [Al(OH&](NOJ3 - 3H20 of 1.877(2) A.” The reaction of InBr, dissolved in a sodium methanolate/methanol mixture with the ligand 1,4,7-tris(2-mercaptoethyl)-1,4,7-triazacyclononane at 20°C produced colourless microcrystals of In(TS-TACN). Single crystals were obtained from a hot aqueous solution upon slow cooling. Figure 2 shows the structure, Table 1 summarizes selected bond distances and angles. The ligand is hexadentate providing a fuc-N3S3 donor set around the indium(II1) metal ion. As Moore et al. have discussed for Ga(TS-TACN) the coordinated ligand TS-TACN has three different sources of chirality. The 1,4,7-triazacyclononane backbone adopts either a (666), or (U&, conformation, the three pendent arms have either (6&Q,, or(U), configuration and, in addition, may adopt (U), or (6&Q conformation in either configuration. In crystals of Ga(TS-TACN) * 2CH2C12 both enantiomeric forms of the neutral complex A(J.U),(&V), and A(&@@.~), are present in the centric unit cell of the space group P2,/n. In(TSTACN) crystallizes in the same space group and the same enantiomers are present [A(U),(&?), and A(~&I),(U.),], despite the fact that the M-N and M-S bond distances increase by 0.189 and 0.172 A, respectively, on going from Ga3+ to In3+. These differences reflect quite accurately the enormous difference of effective ionic radii of 0.18 8, between six-coordinate Ga3+ and In3+. We conclude from these observations that the ligand TS-TACN exhibits more flexibility towards average
U. BOSSEK et al.
Fig. 2. The structure of In(TS-TACN).
binding of small and large metal ions than its counterpart TCTA with three acetate pendent arms. EXPERIMENTAL The compound Al(TCTA) and the ligand 1,4,7tris(2-mercaptoethyl)-1,4,7-triazacyclononane (TSTACN) were synthesized according to published procedures. 5,I2 Synthesis of In(TS-TACN)
Sodium metal (0.15 g) was carefully dissolved in dry ethanol (25 cm3) and InBr, (0.35 g, 1.0 mmol) was added to this solution. To the clear solution the ligand TS-TACN (0.34 g, 1.0 mmol) was added dropwise with stirring at ambient temperature. After 2-3 h a colourless precipitate of In(TSTACN) formed, which was collected by filtration, washed with ethanol and diethylether and air-dried. Needle shaped, colourless crystals suitable for Xray crystallography were obtained from recrystallization from a hot water solution (9YC) which was allowed to slowly cool to 20°C (yield : 0.18 g, 43%). Found: C, 34.4; H, 5.8; N, 9.8; S, 22.6. Calc. for C12H24N3S31n: C, 34.2; H, 5.7; N, 10.0; S, 22.8%. Crystal structure determinations Crystal data. [C i2HI eN306A1], M = 327.27, monoclinic, space group P2,/n, a = 8.803(6),
b = 13.526(9), c = 11.983(6) A, /3 = 105.43(5)“, U = 1375.4 A’ (from 28 values for 25 reflections measured at 15” < 26 < 37”), I = 0.71073 A, T = 298 K, Z = 4, D, = 1.58 g cn- 3, ~(MoK,) = 0.18 nun’. [C12H24N3S31n],A4 = 421.35, monoclinic, space a = 7.292(l), b = 16.807(4), P2 IIn, group c = 13.107(2) A, /? = 93.69(2)“, U = 1603.0 A’ (from 28 values for 25 reflections measured at 22 < 20 < 40”), A = 0.71073 A, T = 298 K, Z = 4, D, = 1.75 g cmp3, ~(Mo-K,) = 1.82 mm-‘. Data processing and structure solution. Intensity data were collected using a Syntex R3 diffractometer, equipped with a graphite monochromator and an MO-K, radiation source (e-scans). Data were corrected for Lorentz and polarization effects in the usual manner and absorption corrections (+scans of seven reflections) were also carried out in both cases. For Al(TCTA) 4500 reflections were measured (28,,, = 60”, h -ll-+8, k O-16, I 0- 16) yielding 2694 with I > 2.50(I) ; for In(TSTACN) 5 144 reflections were measured (28, = k O-20, I O-+18) yielding 3809 60”, h -10-11, with Z 2 2.50(Z). Both structures were solved by Patterson and difference-Fourier methods, and refined by standard least-squares techniques (SHELXTL PLUS program system). The positions of the hydrogen atoms were calculated and included in the refinement with a common isotropic thermal parameter (Vi,, = 0.080 A’) ; all other atoms were refined with anisotropic thermal parameters. The weighting scheme w-i = a’(F) was used throughout. For Al(TCTA) refine-
Pendent arm macrocyclic complexes ment converged with R = 0.049,R, = 0.048and for In(TS-TACN) with R = 0.032,R, = 0.029. Neutral atom scattering factors and anomalous dispersion data were taken from ref. 16. Final difference maps had no chemically significant maxima. Thermal parameters, fractional atom coordinates, listings of observed and calculated structure 8. factors have been deposited with the Editor, from whom copies are available on request. Atom coor9. dinates have also been deposited with the Cambridge Crystallographic Data Centre. 10. 11.
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