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The structure of a 7-coordinate cadmium(II) complex of a marocyclic ligand containing both bridging and uncoordinated perchlorate groups
Z inorg, nueL Chem. Vol. 40, pp. 1595-1596 © Pergamon Press Ltd., 1978. Pr~nteclin Great Britain
0022-190217810801-1595I$02.0010
NOTES
cadmium(H) complex of a macrocyclic l i g a n d c o n t a i n i n g both bridging and uncoordinated perchlorate groups
T h e s t r u c t u r e of a 7 - c o o r d i n a t e
(Received 9 September 1977; received.for publication 14 December 1977) The use of multidentate ligands of special design in leading to unusual coordination geometries in metal complexes has been well illustrated in recent years. Some stalking examples[l-5] of this effect are found in the structural chemistry of metal complexes of pentadentate macrocyclic ligands of the type
N
N [2,2,2-N5]; m = n = 2 [2,3,2-Ns];
L__..
.N_J
m = 2, n = 3
[ 3 , 2 , 3 - N 5 ] ; m = 3, n = 2
From single crystal X-ray and other studies of an extensive range of such complexes we have shown that while the largest, and apparently most flexible, macrocycle [3,2,3-Ns] can accommodate either to an approximately planar or to a folded conformation in metal complexes of variable coordination number (five, six or seven)[4, 5], only relatively undistorted 7-coordinate (pentagonal bipyramidal) structures have so far been found for complexes of the 15-membered ring [2,2,2-N5)[1-3]. In these, the five ring donor atoms define the pentagonal plane, the axial positions being occupied by unidentate anions or solvent molecules. We were therefore interested in the report by Stotter[6] in this journal of the complex Cd(2,2,2-Nbs)(CIO4)2 for which it was proposed that the metal is 5-coordinate possibly with the macrocycle folded. This conclusion rested on the observation that the strong CIO4- band around Ii00cm -t in the mull IR spectrum was not split and on the electrical conductance in the "poorly coordinating" solvent nitromethane which showed it to be a 2:1 electrolyte. The spectrum reported by Stotter conflicted with that obtained by ourselves on a sample of the same complex prepared from Cd(CIO4)2"6HzO (Stotter used CdCI2.2.5H20 as starting salt). In our case we noted splitting of both the ll00cm -~ (v3) and - 6 2 0 c m -~ (v4) modes of the CIO4- ion. Comparison of this spectrum with that of the complex [Cd(2,2,2Ns)Brl,, [Cd~Brt],~12, believed to contain planar Cd(2,2,2-N~) units bridged by Br- ion in a polymeric structure, allowed the assignment of bands at ll30(sh), 1090 and 1050era -t and at 628, 615 and 608 cm -m to CIO~-, clearly indicating that at least one of the two CIO4- ions is coordinated[8]. Possible structures for the complex would therefore seem to be (i) pentagonal bipyramidal with two monodentate CIO4- groups, (ii) pentagonal bipyramidal with one bridging CIO4- group, and (ili) pentagonal pyramidal with one monodentate C104- group. Coordination via one oxygen atom or by two oxygen atoms lowers the symmetry of the C104ion from Ta to C3o and C2~, respectively. In each case, the degeneracy of the asymmetric stretching modes (v3) and the bending modes (u4) is lifted; moreover, the totally symmetric stretch, forbidden in Ta symmetry, may become allowed.
Monodentate CIO4- is quite common and for such compounds three bands are usually observed in the 900-1200 cm -I region[8]. Many fewer cases of bridging CIO4- are established. In Me3Sn(C104)[9] and in Me3Ta(ClO4)z[10], both believed to contain only bridging CIO4-, four bands have been found in this region. However, we did not feel able to make a distinction on the basis of IR spectra alone. A single crystal X-ray structure determination was therefore undertaken not only to elucidate the environment of the perchlorate ions but also to determine the conformation of the macrocycle. The complex was prepared by reaction of 2,6-diacetylpyridine (0.01 tool) with 3,6-diazaoctane-l,8-diamine (0.01 mol) in the presence of Cd(CIO4)2.6HzO (0.01 tool) in refluxing methanol (300 cm 3) containing 3 cm 3 glacial acetic acid for 6 h. Removal of most of the solvent and recrystallization of the crude product from methanol yielded colourless crystals in 65% yield. Found: C, 30.8; H, 3.9; N, 11.9%. CtsHz3NsCI2OsCd requires: C, 30.8; H, 4.0; N, 12.0%. Crystal data. CtsH23NsCI2OsCd, M=.584.5, Monoclinic, a = 11.309(5), b--7.236(5), c = 13.555(8)/~, /3 = 104.68(8), U = 1072.9,~ 3, de= 1.80, Z = 2 . MoK,, radiation, X=0.7107.~. Spacagroup P21 or P2~I,~ from systematic absences OkO, k = 2n+ 1. 975 independent reflections significantly above background with 20 < 40o were measured on a General Electric XRD 5 diffractometer by the stationary-crystal-stationary-counter method. The structure was refined in spacegroup P2~j,, with a disordered model in which atoms in the Cd(2,2,2,-Ns) moiety were either fixed on the mirror plane or positioned both sides with occupancies of -~. Cadmium and chlorine atoms were given anisotropic, and carbon, nitrogen and oxygen atoms, isotropic thermal parameters and the structure refined by full-matrix least squares to R 0.10. Refinement in P2~, while giving the expected lower R value, gave more unreasonable dimensions. Despite the disorder, the main features of the structure are clear and shown in Fig. 1. The structure consists of planar Cd(2,2,2-Ns) moieties bridged by perchlorate anions situated on mirror planes. In addition, there are uncoordinated and severely disordered perchlorate anions also on mirro~ planes. The metal atoms are seven-coordinate with a geometry close to ideal pentagonal bipyramidal as I found so far for all other complexes of this macrocycle[l-3]. As noted above there are rather few cases of the perchlurate ion acting as a bridge between metal atoms. The best authenicated examples are found in a series of complexes between silver perchiorate and aromatics[Ill. These include (we have chosen those with the shortest A g O bonds) anthracenetetrakis (silver perchlorate) monohydrate in which the Ag--O bond lengths are 2.410(6), 2.485(7)*A and bis.(m-xylene) silver perchlorate in which the Ag--O distance is 2.49 A. These bond lengths are appreciably longer than the Ag(1)--O single bond length (21.-2.2 A) so that the metal-perchlorate bonds must be considered weak. In the present molecule the Cd-O distances.also appear to be longer than is usually found, being 2.47(2)A compared to Cd-N of 2.31(2)- 2.41(3) A. By comparison, in a similar 7-coordinate complex [12] of an "N302" pentadentate ligaa_d the shortest Cd--O ' and Cd-N distances are comparable at 2.27 A. It is somewhat surprising that the metal should prefer bridging 1595
1596
Notes
• ' ' Fig. 1. Thestructureofthepolymericcation[Cd(2,2,2-Ns)(CIO4)]~ n + .Therepeatdlstancelsb.Openctrcles:Cd(large), CI (medium), C (small). Closed circles: N, half-open circles: O.
CIO,- ions for axial ligation rather than monodentate CIO4- as found [13] in a Mn(II) complex of a closely related macrocycle. It is difficult to know whether the reason is chemical or purely crystallographic in origin. However, it is interesting to note that a similar situation occurs in at least two other 7-coordinate Cd(ll) complexes and in a 7-coordinate Hg(II) complex of the same class of planar macrocyclic ligand. Thus, in the complex [Cd(2,2,2-Ns)Br]~[Cd2Br6]~/2 noted above[7] and in [M(2,3,2N~)Br]n [MBr4],n (M = Cd or Hg)[5] the metal ions are linked via bridging Br-. Finally, in the light of the structure determination, and by comparison with the spectra of complexes known to contain only ionic CIO,-, we can now assign the infrared bands occurring at ll30(sh), 1050, 628 and 608cm -~ to the bridging CIO4- group.
Department of Chemistry The University Reading RG6 2AD England
M.G.B. DREW S. HOLLIS
Department of Chemistry Queen's University Belfast BT9 5AG N. Ireland
S.G. McFALL S.M. NELSON
RFA~_,qENCES 1. M. G. B. Drew, A. H. Othman, P. D. A. Mcllroy and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 2507 (1975); E. Fleischer and S. Hawkinson, J. Am. Chem. Soc. sg, 720 (1967). 2. M. G. B. Drew, A. H. Othman and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 1394 (1976). 3. M. G. B. Drew, A. H. Othman, S. G. McFall and S. M. Nelson, Chem. Comm. 818 (1975). 4. M. G. B. Drew, A. H. Othman, S. G. McFall, P. D. A. Mcllroy and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 438 (1977). 5. S. M. Nelson, S. G. McFall, M. G. B. Drew, A. H. Othman and N, B. Mason, Chem. Comm. 167 (1977). 6. D. A. Stotter, J. lnorg. Nucl. Chem. 3$, 1866 (1976). 7. S. G. McFall, unpublished results. 8. B. J. Hathaway and A. E. Underhill, J. Chem. Soc. 3091 (1961); F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 3rd Edn, p. 644. lnterscience, New York (1972). 9. H. C. Clark and R. J. O'Brien, lnorg. Chem. 2, 740 (1963). 10. C. Santini-Scampucci and G. Wilkinson, J, Chem. $oc. (Dalton Trans.) 807 (1976). 11. E. A. H. Griflith and E. U Aroma, J. Am. Chem. Soc. 96, 5407 (1974)~ E. F. Taylor, E. A. Hall and E. L. Aroma, J. Am. Chem. Soc. 91, 574.5 (1969). 12. D. C. Liles, M. McPartlin, P. A. Tasker, H. C. Lip and L. F. Lindoy, Chem. Comm. 549 (1976). 13. N. W. Alcock, D. C. Lines, M. McPartlin and P. A. Tasker, Chem. Comm. 727 (1974).
0022-190217S10801=1597/$02.0010
.~ inorg, nacl. Chem. Vol. 40. pp. 1596-1597 © Pergamon Press Lat,, 1978.
Printed in Great Britain
Base hydrolysis of cis(chloro) (benzimidazole) bis(ethylenediamine) cobalt(Ill) cation
(Received 26 August 1977; received/or publication 14 December 1977) We have recently investigated the kinetics of aquation of cis[CoX L(ea):]2+ where X = CI, Br and L = imidazole (imH) and benzimidazole (bzimH)[l,2]. The imido base cis[CoX(L-~ H) (enh] ~ resulting from the pyrrole ionisation of coordinated imidazole and benzimidazole were detected by kinetic and equil-
ibrium studies. Such species were found to undergo aquation at rates much faster than their amine analogues. The imido base of the imidazole complex, cis[CoCl(imH)(enh]2+was also found to undergo second order base hydrolysis. Recently Fenemor and House[3] investigated the stereochemical consequences of the
0022-190217810801-1595I$02.0010
NOTES
cadmium(H) complex of a macrocyclic l i g a n d c o n t a i n i n g both bridging and uncoordinated perchlorate groups
T h e s t r u c t u r e of a 7 - c o o r d i n a t e
(Received 9 September 1977; received.for publication 14 December 1977) The use of multidentate ligands of special design in leading to unusual coordination geometries in metal complexes has been well illustrated in recent years. Some stalking examples[l-5] of this effect are found in the structural chemistry of metal complexes of pentadentate macrocyclic ligands of the type
N
N [2,2,2-N5]; m = n = 2 [2,3,2-Ns];
L__..
.N_J
m = 2, n = 3
[ 3 , 2 , 3 - N 5 ] ; m = 3, n = 2
From single crystal X-ray and other studies of an extensive range of such complexes we have shown that while the largest, and apparently most flexible, macrocycle [3,2,3-Ns] can accommodate either to an approximately planar or to a folded conformation in metal complexes of variable coordination number (five, six or seven)[4, 5], only relatively undistorted 7-coordinate (pentagonal bipyramidal) structures have so far been found for complexes of the 15-membered ring [2,2,2-N5)[1-3]. In these, the five ring donor atoms define the pentagonal plane, the axial positions being occupied by unidentate anions or solvent molecules. We were therefore interested in the report by Stotter[6] in this journal of the complex Cd(2,2,2-Nbs)(CIO4)2 for which it was proposed that the metal is 5-coordinate possibly with the macrocycle folded. This conclusion rested on the observation that the strong CIO4- band around Ii00cm -t in the mull IR spectrum was not split and on the electrical conductance in the "poorly coordinating" solvent nitromethane which showed it to be a 2:1 electrolyte. The spectrum reported by Stotter conflicted with that obtained by ourselves on a sample of the same complex prepared from Cd(CIO4)2"6HzO (Stotter used CdCI2.2.5H20 as starting salt). In our case we noted splitting of both the ll00cm -~ (v3) and - 6 2 0 c m -~ (v4) modes of the CIO4- ion. Comparison of this spectrum with that of the complex [Cd(2,2,2Ns)Brl,, [Cd~Brt],~12, believed to contain planar Cd(2,2,2-N~) units bridged by Br- ion in a polymeric structure, allowed the assignment of bands at ll30(sh), 1090 and 1050era -t and at 628, 615 and 608 cm -m to CIO~-, clearly indicating that at least one of the two CIO4- ions is coordinated[8]. Possible structures for the complex would therefore seem to be (i) pentagonal bipyramidal with two monodentate CIO4- groups, (ii) pentagonal bipyramidal with one bridging CIO4- group, and (ili) pentagonal pyramidal with one monodentate C104- group. Coordination via one oxygen atom or by two oxygen atoms lowers the symmetry of the C104ion from Ta to C3o and C2~, respectively. In each case, the degeneracy of the asymmetric stretching modes (v3) and the bending modes (u4) is lifted; moreover, the totally symmetric stretch, forbidden in Ta symmetry, may become allowed.
Monodentate CIO4- is quite common and for such compounds three bands are usually observed in the 900-1200 cm -I region[8]. Many fewer cases of bridging CIO4- are established. In Me3Sn(C104)[9] and in Me3Ta(ClO4)z[10], both believed to contain only bridging CIO4-, four bands have been found in this region. However, we did not feel able to make a distinction on the basis of IR spectra alone. A single crystal X-ray structure determination was therefore undertaken not only to elucidate the environment of the perchlorate ions but also to determine the conformation of the macrocycle. The complex was prepared by reaction of 2,6-diacetylpyridine (0.01 tool) with 3,6-diazaoctane-l,8-diamine (0.01 mol) in the presence of Cd(CIO4)2.6HzO (0.01 tool) in refluxing methanol (300 cm 3) containing 3 cm 3 glacial acetic acid for 6 h. Removal of most of the solvent and recrystallization of the crude product from methanol yielded colourless crystals in 65% yield. Found: C, 30.8; H, 3.9; N, 11.9%. CtsHz3NsCI2OsCd requires: C, 30.8; H, 4.0; N, 12.0%. Crystal data. CtsH23NsCI2OsCd, M=.584.5, Monoclinic, a = 11.309(5), b--7.236(5), c = 13.555(8)/~, /3 = 104.68(8), U = 1072.9,~ 3, de= 1.80, Z = 2 . MoK,, radiation, X=0.7107.~. Spacagroup P21 or P2~I,~ from systematic absences OkO, k = 2n+ 1. 975 independent reflections significantly above background with 20 < 40o were measured on a General Electric XRD 5 diffractometer by the stationary-crystal-stationary-counter method. The structure was refined in spacegroup P2~j,, with a disordered model in which atoms in the Cd(2,2,2,-Ns) moiety were either fixed on the mirror plane or positioned both sides with occupancies of -~. Cadmium and chlorine atoms were given anisotropic, and carbon, nitrogen and oxygen atoms, isotropic thermal parameters and the structure refined by full-matrix least squares to R 0.10. Refinement in P2~, while giving the expected lower R value, gave more unreasonable dimensions. Despite the disorder, the main features of the structure are clear and shown in Fig. 1. The structure consists of planar Cd(2,2,2-Ns) moieties bridged by perchlorate anions situated on mirror planes. In addition, there are uncoordinated and severely disordered perchlorate anions also on mirro~ planes. The metal atoms are seven-coordinate with a geometry close to ideal pentagonal bipyramidal as I found so far for all other complexes of this macrocycle[l-3]. As noted above there are rather few cases of the perchlurate ion acting as a bridge between metal atoms. The best authenicated examples are found in a series of complexes between silver perchiorate and aromatics[Ill. These include (we have chosen those with the shortest A g O bonds) anthracenetetrakis (silver perchlorate) monohydrate in which the Ag--O bond lengths are 2.410(6), 2.485(7)*A and bis.(m-xylene) silver perchlorate in which the Ag--O distance is 2.49 A. These bond lengths are appreciably longer than the Ag(1)--O single bond length (21.-2.2 A) so that the metal-perchlorate bonds must be considered weak. In the present molecule the Cd-O distances.also appear to be longer than is usually found, being 2.47(2)A compared to Cd-N of 2.31(2)- 2.41(3) A. By comparison, in a similar 7-coordinate complex [12] of an "N302" pentadentate ligaa_d the shortest Cd--O ' and Cd-N distances are comparable at 2.27 A. It is somewhat surprising that the metal should prefer bridging 1595
1596
Notes
• ' ' Fig. 1. Thestructureofthepolymericcation[Cd(2,2,2-Ns)(CIO4)]~ n + .Therepeatdlstancelsb.Openctrcles:Cd(large), CI (medium), C (small). Closed circles: N, half-open circles: O.
CIO,- ions for axial ligation rather than monodentate CIO4- as found [13] in a Mn(II) complex of a closely related macrocycle. It is difficult to know whether the reason is chemical or purely crystallographic in origin. However, it is interesting to note that a similar situation occurs in at least two other 7-coordinate Cd(ll) complexes and in a 7-coordinate Hg(II) complex of the same class of planar macrocyclic ligand. Thus, in the complex [Cd(2,2,2-Ns)Br]~[Cd2Br6]~/2 noted above[7] and in [M(2,3,2N~)Br]n [MBr4],n (M = Cd or Hg)[5] the metal ions are linked via bridging Br-. Finally, in the light of the structure determination, and by comparison with the spectra of complexes known to contain only ionic CIO,-, we can now assign the infrared bands occurring at ll30(sh), 1050, 628 and 608cm -~ to the bridging CIO4- group.
Department of Chemistry The University Reading RG6 2AD England
M.G.B. DREW S. HOLLIS
Department of Chemistry Queen's University Belfast BT9 5AG N. Ireland
S.G. McFALL S.M. NELSON
RFA~_,qENCES 1. M. G. B. Drew, A. H. Othman, P. D. A. Mcllroy and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 2507 (1975); E. Fleischer and S. Hawkinson, J. Am. Chem. Soc. sg, 720 (1967). 2. M. G. B. Drew, A. H. Othman and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 1394 (1976). 3. M. G. B. Drew, A. H. Othman, S. G. McFall and S. M. Nelson, Chem. Comm. 818 (1975). 4. M. G. B. Drew, A. H. Othman, S. G. McFall, P. D. A. Mcllroy and S. M. Nelson, J. Chem. Soc. (Dalton Trans.) 438 (1977). 5. S. M. Nelson, S. G. McFall, M. G. B. Drew, A. H. Othman and N, B. Mason, Chem. Comm. 167 (1977). 6. D. A. Stotter, J. lnorg. Nucl. Chem. 3$, 1866 (1976). 7. S. G. McFall, unpublished results. 8. B. J. Hathaway and A. E. Underhill, J. Chem. Soc. 3091 (1961); F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 3rd Edn, p. 644. lnterscience, New York (1972). 9. H. C. Clark and R. J. O'Brien, lnorg. Chem. 2, 740 (1963). 10. C. Santini-Scampucci and G. Wilkinson, J, Chem. $oc. (Dalton Trans.) 807 (1976). 11. E. A. H. Griflith and E. U Aroma, J. Am. Chem. Soc. 96, 5407 (1974)~ E. F. Taylor, E. A. Hall and E. L. Aroma, J. Am. Chem. Soc. 91, 574.5 (1969). 12. D. C. Liles, M. McPartlin, P. A. Tasker, H. C. Lip and L. F. Lindoy, Chem. Comm. 549 (1976). 13. N. W. Alcock, D. C. Lines, M. McPartlin and P. A. Tasker, Chem. Comm. 727 (1974).
0022-190217S10801=1597/$02.0010
.~ inorg, nacl. Chem. Vol. 40. pp. 1596-1597 © Pergamon Press Lat,, 1978.
Printed in Great Britain
Base hydrolysis of cis(chloro) (benzimidazole) bis(ethylenediamine) cobalt(Ill) cation
(Received 26 August 1977; received/or publication 14 December 1977) We have recently investigated the kinetics of aquation of cis[CoX L(ea):]2+ where X = CI, Br and L = imidazole (imH) and benzimidazole (bzimH)[l,2]. The imido base cis[CoX(L-~ H) (enh] ~ resulting from the pyrrole ionisation of coordinated imidazole and benzimidazole were detected by kinetic and equil-
ibrium studies. Such species were found to undergo aquation at rates much faster than their amine analogues. The imido base of the imidazole complex, cis[CoCl(imH)(enh]2+was also found to undergo second order base hydrolysis. Recently Fenemor and House[3] investigated the stereochemical consequences of the