Synthesis of a heteroditopic cryptand capable of imposing a distorted coordination geometry onto Cu(II): Crystal structures of the cryptand (L), [Cu(L)(CN)](picrate), and [Cu(L)(NCS)](picrate) and spectroscopic studies of the Cu(II) complexes

Article abstract of DOI:10.1021/ic950933+

The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde, tris{[2-(3-(oxomethyl)phenyl)oxy]ethyl}amine at 5°C temperature. The crystal structure of L (P2₁/c, a = 10.756 (5) A?, b = 27.407(9) ?A, c = 12.000(2) A?, β= 116.22(3)°, Z = 4, R = 0.060, R_w = 0.058) shows a pseudo-3-fold symmetry axis passing through the two bridgehead nitrogens. This symmetry is maintained in chloroform solution also, as indicated from its ¹H-NMR spectral data. The cryptand readily forms inclusion complexes with the Cu(II) ion at the tren end of the cavity. The tetracoordinated Cu(II) cryptate (1) thus formed with Cu(picrate)₂ exhibits a very small An value (60 × 10^-4 cm^-1) in its EPR spectrum and low-energy ligand field bands in its electronic spectrum in MeCN at room temperature. The bound Cu(II) ion readily accepts the anions CN^-, SCN^-, or N₃^-, forming distorted trigonal bipyramidal complexes (2-4). The crystal structure of [Cu(L)(CN)](picrate) (2) (P2₁/C, a = 13.099(1) A?, b = 11.847(8) A?, c = 25.844(7) A?, β = 91.22(1)°, Z = 4, R = 0.056, R_w = 0.054) has been determined. The equatorial coordination is provided by the three secondary amino N atoms of the tren unit in L, while the two axial positions are occupied by the bridgehead N of the tren unit and the C atom of the cyanide group. One of the equatorial Cu - N bond distances is 2.339(6) A°, which is longer than normal values. The crystal structure of [Cu(L)(NCS)](picrate) (3) (C2/c, a = 47.889(10) A?, b = 10.467(5) A?, c = 16.922(2) A?, β = 93.90(2)°, Z = 8, R = 0.054, R_w = 0.055) shows the coordination geometry around the Cu(II) ion to be very similar to that in the case of 2. The electronic spectral and EPR spectral data obtained on 2-4 are characteristic of trigonal bipyramidal Cu(II) complexes. The three meta-substituted benzene rings present in L makes the donor atom somewhat rigid in nature which enforces a distorted geometry around the Cu(II) ion.

Full text of DOI:10.1021/ic950933+

3380
Inorg. Chem. 1996, 35, 3380-3387
Synthesis of a Heteroditopic Cryptand Capable of Imposing a Distorted Coordination
Geometry onto Cu(II): Crystal Structures of the Cryptand (L), [Cu(L)(CN)](picrate), and
[Cu(L)(NCS)](picrate) and Spectroscopic Studies of the Cu(II) Complexes
Dillip K. Chand and Parimal K. Bharadwaj*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
ReceiVed July 27, 1995X
The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good
yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde,
tris{[2-(3-(oxomethyl)phenyl)oxy]ethyl}amine at 5 °C temperature. The crystal structure of L (P21/c, a ) 10.756
(5) Å, b ) 27.407(9) Å, c ) 12.000(2) Å, â ) 116.22(3)°, Z ) 4, R ) 0.060, Rw ) 0.058) shows a pseudo-3-fold
symmetry axis passing through the two bridgehead nitrogens. This symmetry is maintained in chloroform solution
1
also, as indicated from its H-NMR spectral data. The cryptand readily forms inclusion complexes with the
Cu(II) ion at the tren end of the cavity. The tetracoordinated Cu(II) cryptate (1) thus formed with Cu(picrate)2
exhibits a very small AII value (60 × 10-4 cm-1) in its EPR spectrum and low-energy ligand field bands in its
electronic spectrum in MeCN at room temperature. The bound Cu(II) ion readily accepts the anions CN-, SCN-,
or N3-, forming distorted trigonal bipyramidal complexes (2-4). The crystal structure of [Cu(L)(CN)](picrate)
(2) (P21/C, a ) 13.099(1) Å, b ) 11.847(8) Å, c ) 25.844(7) Å, â ) 91.22(1)°, Z ) 4, R ) 0.056, Rw ) 0.054)
has been determined. The equatorial coordination is provided by the three secondary amino N atoms of the tren
unit in L, while the two axial positions are occupied by the bridgehead N of the tren unit and the C atom of the
cyanide group. One of the equatorial Cu-N bond distances is 2.339(6) Å, which is longer than normal values.
The crystal structure of [Cu(L)(NCS)](picrate) (3) (C2/c, a ) 47.889(10) Å, b ) 10.467(5) Å, c ) 16.922(2) Å,
â ) 93.90(2)°, Z ) 8, R ) 0.054, Rw ) 0.055) shows the coordination geometry around the Cu(II) ion to be very
similar to that in the case of 2. The electronic spectral and EPR spectral data obtained on 2-4 are characteristic
of trigonal bipyramidal Cu(II) complexes. The three meta-substituted benzene rings present in L makes the
donor atom somewhat rigid in nature which enforces a distorted geometry around the Cu(II) ion.
Introduction
metal cryptates, which bind the substrates of compatible size
between both of the complexed metal ions in a cascade fashion,
while such complexes of mononuclear cryptates are very rare.10
The present ligand has been synthesized by keeping all these
aspects in mind. Herein, we report our first results in this area.
The new macrobicyclic heteroditopic cryptand (L) was synthe-
sized by [1 + 1] condensation of a new tripodal trialdehyde
with tris(2-aminoethyl)amine (tren). We and others have
described the synthesis of macrobicyclic molecules using alkali/
alkaline earth metal ions as templates.11-13 Recently, a mac-
robicyclic cryptand has been synthesized14 by [2 + 3] conden-
sation of tren with glyoxal at low temperature. The present
cryptand L has been synthesized in multigram scale at low
temperature without using any templating metal ions. The
cryptand is well-suited to accommodate a transition metal ion
at the tren end of the cavity, leaving an empty space to enable
inorganic anions to enter and get bonded to the metal ion.
The aim of the present work is to probe whether the donor
atom in the cryptand can impose a distorted geometry onto
Cu(II) and whether simple inorganic anions like CN-, SCN-,
Cryptands as ligands for transition metal ions are of consider-
able current interest.1-4 In a cryptand, the donor atoms’
topology as well as their rigidity can be varied via ligand design.
Therefore, with these molecules imposition of a desired
geometry onto a coordinating metal ion can be achieved.5
Imposition of an unusual coordination geometry in turn will
lead to new electronic structure and bonding of the metal
complex formed. A heteroditopic cryptand can be designed so
that a metal ion can recognize only one receptor site, leaving
the other side empty. It will be possible for an inorganic/organic
group to occupy this vacant site, thereby forming cascade
complexes. These type of complexes are formed via a
sequential double selection process, (a) binding of the cation
by the ligand’s donor atoms and (b) selection of the substrate
controlled by the nature and arrangement of the complexed
cation. In literature there are a few examples1,6-9 of binuclear
X Abstract published in AdVance ACS Abstracts, April 15, 1996.
(1) Bazzicalupi, C.; Bencini, A.; Bianchi, A.; Fusi, V.; Mazzanti, L.;
Paoletti, P.; Valtancoli, B. Inorg. Chem. 1995, 34, 3003.
(2) Pierre, J.-L.; Chautemps, P.; Refaif, S. M.; Beguin, C. G.; El-Marzouki,
A.; Serratric, G.; Rey, P.; Laugier, J. J. Chem. Soc., Chem. Commun.
1994, 1117.
(3) Drew, M. G. B.; Howarth, O. W.; Morgan, G. G.; Nelson, J. J. Chem.
Soc., Dalton. Trans. 1994, 3149.
(4) Yan, Y. S.; Hui, L. Q.; Chang, S. M. Inorg. Chem. 1994, 34, 1251.
(5) Bharadwaj, P. K. J. Sci. Ind. Res. (India) 1993, 52, 533.
(6) Lehn, J.-M.; Pine, S. H.; Watanbe, E.; Willard, A. K. J. Am. Chem.
Soc. 1977, 99, 6766.
-
and N3 can add onto the metal ion inside the cavity. Herein
(9) Menif, R.; Reibenspies, J.; Martell, A. E. Inorg. Chem. 1991, 30, 3446.
(10) Motekaitis, R. J.; Martell, A. E.; Dietrich, B.; Lehn, J.-M. Inorg. Chem.
1984, 23, 1588.
(11) Ragunathan, K. G.; Shukla, R.; Mishra, S.; Bharadwaj, P. K.
Tetrahedron Lett. 1993, 34, 5631.
(12) Ghosh, P.; Shukla, R.; Chand, D. K.; Bharadwaj, P. K. Tetrahedron
1995, 51, 3265.
(13) Hunter, J.; Nelson, J.; Harding, C.; McCann, M.; McKee. V. J. Chem.
Soc., Chem. Commun. 1990, 1148.
(7) Motekaitis, R. J.; Martell, A. E.; Lehn, J.-M.; Watanabe, E. Inorg.
Chem. 1982, 21, 4253.
(8) Motekaitis, R. J.; Martell, A. E.; Murase, I.; Lehn, J.-M.; Hosseini,
M. W. Inorg. Chem. 1988, 27, 3630.
(14) Smith, P. H.; Barr, M. E.; Brainard, J. R.; Ford, D. K.; Freiser, H.;
Muralidharan, S.; Reilly, S. B.; Ryan, R. R.; Silks, L. A., III; Yu, W.
J. Org. Chem. 1993, 58, 7939.
S0020-1669(95)00933-5 CCC: $12.00 © 1996 American Chemical Society

A Heteroditopic Cryptand
Inorganic Chemistry, Vol. 35, No. 11, 1996 3381
mixture with 3 × 50 cm3 of CHCl3. The organic layer was washed
several times with water, then dried over anhydrous Na2SO4, and finally
treated with activated charcoal. Triald was obtained by evaporating
the organic layer as a pale yellow semisolid; yield, 80%. IR (KBr
pellet, cm-1): νmax 1690 s. 1H-NMR (80 MHz, CDCl3): δ 3.2 (t, 6H),
4.2 (t, 6H), 7.3 (m, 12H), 10.0 (s, 3H).
Scheme 1. Synthesis of the Cryptand L
Cryptand, L. Triald (3.68 g, 8 mmol) was taken in 400 cm3 of
the mixed solvent system THF:MeOH (1:10 ratio by volume), in a
2000 cm3 round bottomed flask at 278 K. To this solution was added
a solution of tris(2-aminoethyl)amine (1.17 g, 8 mmol) in 300 cm3 of
MeOH over a period of 12 h, while the temperature was maintained at
278 ( 1 K and the mixture was stirred continuously. The addition
was adjusted so as to disperse a drop before another drop can fall into
the reaction mixture. At the end of the addition, the reaction was carried
out simply by stirring at room temperature for a period of 12 h.
Reduction of the Schiff base thus formed was achieved by hydrogenat-
ing it with an excess of NaBH4 (∼1.6 g) at room temperature for 2 h
followed by refluxing for another 2 h. The solvent was evaporated
until it was almost dry, and the residue was treated with 40 cm3 of
cold water. The desired cryptand L was extracted with 4 × 50 cm3 of
CHCl3. The organic layer was dried over anhydrous Na2SO4 and
evaporated to obtain a pale yellow solid. The solid washed with 50
cm3 of MeCN and dried in air; yield, 39% (mp, 125 °C). 1H-NMR
(80 MHz, CDCl3): δ 1.9 (s, 3H), 2.65 (s, 12H), 3.05 (t, 6H), 3.6 (s,
6H), 4.0 (t, 6H), 6.9 (m, 12H). 13C-NMR (20.1 MHz, CDCl3): δ 48.10,
54.00, 55.90, 56.41, 68.03, 113.20, 114.63, 120.70, 129.17, 142.40,
159.75. FAB-MS: m/z 560 (M + 1)+. Anal. Calcd. for C33H45-
N5O3: C, 70.81; H, 8.10; N, 12.51. Found: C, 70.27; H, 8.31; N,
12.42. Crystals of this compound suitable for X-ray analysis were
grown by slow evaporation of a dilute solution with the mixed MeOH:
MeCN solvent (1:1 by volume) at room temperature.
we report the synthesis of L and its ligating characteristics
toward the Cu(II) ion.
[Cu(L)](picrate)2, 1. To L (0.056 g, 0.1 mmol) dissolved in 5 cm3
of MeOH was added Cu(picrate)2 (0.052 g, 0.1 mmol) dissolved in 5
cm3 of MeOH. A green solid separated immediately that was collected
by filtration, washed with MeOH and air-dried. The solid, upon
recrystallization from MeCN, afforded a green crystalline solid in 90%
overall yield which was dried under vacuum at 40 °C (mp (dec.), 150
°C). Anal. Calcd for C45H49N11O17Cu: C, 50.07; H, 4.58; N, 14.27.
Found: C, 49.83; H, 4.72; N, 14.08.
Experimental Section
Materials. Reagent grade tris(2-aminoethyl)amine, 3-hydroxyben-
zaldehyde (Aldrich), and triethanolamine (Glaxo) were used as received.
Thionyl chloride and all of the solvents (SD Fine Chemicals) were
purified prior to use by following standard procedures.15
Synthesis. Tris{[2-(3-(oxomethyl)phenyl)oxy]ethyl}amine, Tri-
ald. To a solution of 3-hydroxybenzaldehyde (7.33 g; 60 mmol) in
propanol (200 cm3) was added crushed NaOH (3.2 g, 80 mmol) and
stirred at 303 K for 30 min. To the resulting brown solution, solid
tris(2-chloroethyl)amine hydrochloride16 (4.8 g; 20 mmol) was added
at once, and the mixture was heated under reflux for 4 h. After this
period, the brown solution was allowed to cool to room temperature
and poured into 200 cm3 of cold water. Triald was extracted from this
[Cu(L)(CN)](picrate), 2. Complex 1 (0.109 g, 0.1 mmol) was
dissolved in 10 cm3 of MeCN and treated with NaCN (0.005 g,
0.1mmol) dissolved in 2 cm3 of MeOH with warming at 50 °C. Upon
addition of NaCN, the color of the solution became dark green. The
solution was filtered and allowed to evaporate slowly at room
Table 1. Crystallographic and Experimental Data for L, {[Cu(CN)]L}(picrate) (2) and {[Cu(NCS)]L}(picrate) (3)
L
(2)
(3)
formula
MW
temp, °C
C33H45N5O3
559.758
25
C40H47N9O10Cu
878.049
25
C40H47N9O10SCu
910.113
25
radiation, graphite monochromated
λ, Å
cryst sys
Mo KR
0.71073
monoclinic
P21/C
Mo KR
0.71073
monoclinic
P21/C
Mo KR
0.71073
monoclinic
C2/c
space group
a,Å
b, Å
c,Å
10.756(5)
27.407(9)
12.000(2)
116.22(3)
3174.5(2)
4
13.099(1)
11.847(8)
25.844(7)
91.22(1)
4009.8(5)
4
47.889(10)
10.467(5)
16.922(2)
93.90(2)
8464.0(4)
8
â, deg
V, Å3
Z
F(000), electrons
500
1.269
0.08
0.20 × 0.30 × 0.50
0.9757, 0.9406
5570
2368
370
699
1.453
0.62
0.20 × 0.30 × 0.30
0.8323, 0.7614
7362
4482
541
715
1.427
0.64
0.15 × 0.20 × 0.40
0.8664, 0.6845
7445
3605
550
D
calcd, g/cm3
µ, mm-1
cryst size, mm3
transmn (max, min)
no. of unique reflcns
no. of reflcns used (I > 2σ(I))
no. of variables
Ra
0.060
0.058
0.056
0.054
0.054
0.055
b
Rw
goodness of fit
2.169
2.917
1.702
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) |∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2, w ) 1/σ(F).

3382 Inorganic Chemistry, Vol. 35, No. 11, 1996
Chand and Bharadwaj
Table 2. Non-Hydrogen Positional and Equivalent Isotropic
Displacement Parameters (Å2) for L (Esds in Parentheses)
atom
x/a
y/b
z/c
U(eq)
O(1)
O(2)
O(3)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
- 0.2274(6)
-0.0170(6)
-0.0747(7)
0.5714(8)
0.2776(8)
-0.2765(8)
0.4900(8)
0.4408(9)
0.517(1)
0.368(1)
0.140(1)
0.0477(9)
0.053(1)
-0.035(1)
-0.1305(9)
-0.1355(9)
-0.047(1)
-0.307)1)
-0.377(1)
-0.235(1)
-0.077(1)
0.123(1)
0.176(1)
0.318(1)
0.404(1)
0.352(1)
0.209(1)
0.373(1)
0.556(1)
0.6514(9)
0.635(1)
0.590(1)
0.387(1)
0.236(1)
0.142(1)
0.004(1)
-0.043(1)
0.051(1)
0.189(1)
-0.218(1)
-0.2840(9)
0.6215(2)
0.5151(3)
0.5430(2)
0.7215(3)
0.7435(3)
0.5178(3)
0.6390(3)
0.6589(3)
0.7712(4)
0.7744(4)
0.7378(3)
0.7113(3)
0.7197(4)
0.6953(4)
0.6614(4)
0.6535(4)
0.6777(3)
0.5911(4)
0.5524(4)
0.4798(4)
0.4719(4)
0.5205(4)
0.5646(4)
0.5739(4)
0.5390(4)
0.4957(4)
0.4847(4)
0.6205(4)
0.6815(4)
0.7050(4)
0.7106(4)
0.6599(4)
0.6107(4)
0.6121(4)
0.5805(4)
0.5770(4)
0.6079(4)
0.6399(4)
0.6428(4)
0.5421(4)
0.5040(4)
0.1187(6)
0.1239(6)
0.3838(6)
0.4850(8)
0.3376(7)
0.1388(8)
0.3169(7)
0.6015(8)
0.4519(9)
0.4384(9)
0.3307(8)
0.2133(9)
0.101(1)
0.084(4)
0.087(4)
0.083(4)
0.080(5)
0.076(4)
0.073(4)
0.087(5)
0.097(5)
0.091(6)
0.083(6)
0.075(5)
0.062(5)
0.082(6)
0.102(6)
0.088(6)
0.068(5)
0.063(5)
0.086(5)
0.085(6)
0.088(6)
0.088(6)
0.070(6)
0.073(6)
0.073(6)
0.089(6)
0.096(6)
0.083(6)
0.085(6)
0.092(6)
0.097(6)
0.105(6)
0.102(6)
0.091(6)
0.083(7)
0.075(6)
0.072(6)
0.094(6)
0.117(7)
0.105(7)
0.087(6)
0.082(6)
-0.0050(9)
-0.0027(9)
0.108(1)
C(9)
0.2151(9)
0.0151(9)
0.0583(9)
0.0799(9)
0.1454(9)
0.1890(9)
0.1734(8)
0.2341(9)
0.313(1)
0.328(10
0.265(1)
0.2071(9)
0.2940(9)
0.419(1)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
Figure 1. ORTEP21 drawing of L showing the thermal ellipsoids and
the atomic numbering scheme. Hydrogen atoms are omitted for clarity.
ca. 1 × 10-3 M in MeCN. Microanalyses were obtained at CDRI,
Lucknow, India. Reported melting points are uncorrected.
0.618(1)
X-ray Structural Studies. X-ray quality crystals were obtained only
with L, 2, and 3. Single crystal X-ray data on them were collected at
room temperature on an Enraf-Nonius CAD4-Mach diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å). The cell
parameters in each case were determined by least-squares refinement
of the diffractometer setting angles for 25 centered reflections that were
in the range 22° e 2θ e 25°. Systematic absences were consistent
with the space group P21/c for both L and 2. For 3, the systematic
absences were consistent with the space groups Cc and C2/c. The
structure was solved and successfully refined in the space group C2/c.
Three standard reflections were measured at every hour to monitor
instrument and crystal stability. The maximum corrections of intensity
based on the standard reflections were less than 1% for each. Intensity
data were corrected for Lorentz and polarization effects; analytical
absorption corrections were applied. The XTAL 3.2 program package17
was used in absorption and all subsequent calculations, utilizing a 486-
DX personal computer (PCL, India) operating at 66 MHz under MS-
DOS version 5. The linear absorption coefficients, scattering factors
for the atoms, and the anomalous-disperson corrections were taken from
the International Tables for X-ray Crystallography.18 The structures
were solved by the direct method19 and successive difference Fourier
syntheses. The refinement was done by full-matrix least-squares
technique using anisotropic thermal parameters for all non-hydrogen
atoms. Some of the H atoms could be located in the difference maps
in each case, the rest were calculated assuming ideal geometries of the
atom concerned. H atom positions or thermal parameters were not
refined.
0.6402(9)
0.6025(9)
0.5752(9)
0.4898(9)
0.4674(9)
0.531(1)
0.617(1)
0.639(1)
0.3526(9)
0.2515(9)
temperature. Overnight, dark green plates appeared which were
collected by filtration and air-dried. A further crop was obtained on
further evaporation of the solvent at room temperature; yield 86% (mp
(dec.) 200 °C) Anal. Calcd for C40H47N9O10Cu: C, 54.72; H, 5.40; N,
14.43. Found: C, 54.19; H, 5.87; N, 14.23.
[Cu(L)(NCS)](picrate), 3. This complex was isolated following
the procedure adopted for 2 except that NH4SCN (0.008 g, 0.1 mmol)
was used instead of NaCN. Dark green rectangular parallelepipeds
were isolated in 80% yield (mp (dec.) 200 °C). Anal. Calcd for C40H47-
N9O10SCu: C, 52.80; H, 5.20; N, 13.92. Found: C, 52.45; H, 5.31;
N, 13.81.
[Cu(L)(N3)](picrate), 4. Dark green thin plates of 4 were isolated
as above in 88% yield (mp (dec.) 175 °C). Anal. Calcd for
C39H47N11O10 Cu: C, 52.43; H, 5.30; N, 17.24. Found: C, 52.21; H,
5.12; N, 16.98.
Caution! The picrate salts must be handled with care as they are
potential explosives.
Results and Discussion
Measurements. Spectroscopic data were collected as follows: IR
(KBr disk, 400-4000 cm-1), Perkin-Elmer Model 1320; electronic
absorption spectra (at 298 K, freshly distilled MeCN as solvent), JASCO
V-570 UV-vis-near-IR spectrophotometer, proton and carbon NMR
(80 and 20.1 MHz, respectively, CDCl3, TMS), Bruker WP-80FT
instrument, FAB mass spectrometry (CHCl3 as solvent, argon as the
carrier gas), JEOL Model SX 102/DA-6000; EPR (X-band at 298 and
77 K, solid and solution), Varian E-109 with solute concentration of
The cryptand L can be easily synthesized via tripod-tripod
Schiff base condensation of one triamine and one trialdehyde
(17) Hall, S. R., Stewart, J. M., Flack, H. B., Eds. The XTAL 3.2 Reference
Manual, Universities of Western Australia and Maryland: and College
Park, MD, 1993.
(18) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(19) Main, P. In Recent DeVlopments in The MULTAN SystemssThe Use
of Molecular Strctures Crystallographic Computing Techniques;
Ahmed, F. R., Huml, K., Sedlacek, B., Eds.; Munksgaard: Copen-
hagen, 1976; p 97.
(15) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. D. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: Oxford, U.K., 1980.
(16) Ward, K., Jr. J. Am. Chem. Soc. 1935, 57, 914.

A Heteroditopic Cryptand
Inorganic Chemistry, Vol. 35, No. 11, 1996 3383
Table 3. Bond Lengths (Å) and Angles (deg) for L (Esds in
parentheses)
O(1)-C(8)
O(1)-C(10)
O(2)-C(13)
O(2)-C(14)
O(3)-C(28)
O(3)-C(32)
N(1)-C(1)
N(1)-C(22)
N(1)-C(23)
N(2)-C(2)
N(2)-C(3)
N(3)-C(11)
N(3)-C(12)
N(3)-C(33)
N(4)-C(20)
N(4)-C(21)
N(5)-C(24)
N(5)-C(25)
C(1)-C(2)
C(3)-C(4)
C(4)-C(5)
C(4)-C(9)
C(5)-C(6)
1.37(1)
1.42(1)
1.43(1)
1.37(1)
1.36(1)
1.42(1)
1.47(1)
1.48(2)
1.46(1)
1.44(1)
1.45(1)
1.44(1)
1.44(1)
1.44(2)
1.45(1)
1.45(1)
1.46(1)
1.44(1)
1.53(2)
1.50(1)
1.39(2)
1.38(2)
1.38(1)
C(6)-C(7)
1.39(2)
1.37(2)
1.39(1)
1.52(2)
1.54(1)
1.39(2)
1.38(1)
1.39(1)
1.38(1)
1.50(2)
1.36(2)
1.41(1)
1.53(1)
1.53(2)
1.51(2)
1.38(1)
1.38(2)
1.39(2)
1.38(2)
1.39(1)
1.39(2)
1.52(1)
C(7)-C(8)
C(8)-C(9)
C(10)-C(11)
C(12)-C(13)
C(14)-C(15)
C(14)-C(19)
C(15)-C(16)
C(16)-C(17)
C(16)-C(20)
C(17)-C(18)
C(18)-C(19)
C(21)-C(22)
C(23)-C(24)
C(25)-C(26)
C(26)-C(27)
C(26)-C(31)
C(27)-C(28)
C(28)-C(29)
C(29)-C(30)
C(30)-C(31)
C(32)-C(33)
Figure 2. ORTEP21 drawing of the cation of 2 showing the thermal
ellipsoids and the atomic numbering scheme. Hydrogen atoms are
omitted for clarity.
and it readily takes up anions like CN-, SCN-, and N3-, forming
pentacoordinated complexes.
C(8)-O(1)-C(10)
118.1(9) O(2)-C(14)-C(15)
115.6(9)
123.0(1)
C(13)-O(2)-C(14) 117.4(8) O(2)-C(14)-C(19)
All of the complexes are stable in air and soluble in common
organic solvents such as MeCN and chloroform. Molecular
conductivity studies for 1-4 in MeCN (ca. 1 × 10-3 M) have
C(28)-O(3)-C(32) 117.1(9) C(15)-C(14)-C(19) 120.9(9)
C(1)-N(1)-C(22)
C(1)-N(1)-C(23)
113.4(9) C(14)-C(15)-C(16) 120.8(9)
115.0(9) C(15)-C(16)-C(17) 119.0(1)
been carried out at 298 K. ΛM for 1 is 221 Ω-1 cm2 mol-1
.
C(22)-N(1)-C(23) 114.9(8) C(15)-C(16)-C(20) 119.3(9)
C(2)-N(2)-C(3)
113.8(9) C(17)-C(16)-C(20) 121.6(9)
This value corresponds20 to a 1:2 electrolyte. For 2-4, the ΛM
values range within 131-149 Ω-1 cm2 mol-1, corresponding20
to 1:1 electrolytes.
C(11)-N(3)-C(12) 116.8(8) C(16)-C(17)-C(18) 120.0(9)
C(11)-N(3)-C(33) 117.8(9) C(17)-C(18)-C(19) 122.3(9)
C(12)-N(3)-C(33) 115.5(8) C(14)-C(19)-C(18) 117.0(1)
C(20)-N(4)-C(21) 114.1(8) N(4)-C(20)-C(16)
C(24)-N(5)-C(25) 113.7(8) N(4)-C(21)-C(22)
111.6(8)
109.0(9)
110.7(8)
110.2(8)
110.4(8)
111.7(9)
Description of the Structures. Cryptand, L. The structure
of L was confirmed by crystallographic analysis. A perspective
view of the molecule showing the atom numbering scheme is
given in Figure 1, while the bond distances and angles are
collected in Table 3. The molecule has an endo-endo
conformation, at least in the solid state, where the distance
between the two bridgehead nitrogens is found to be 9.904(7)
Å. The distances between any two secondary amino N atoms
are similar; the same is true in the case of the ethereal O atoms
or the corresponding C atoms of the three aromatic rings (Table
7). The bridgehead nitrogen and the secondary amino N atoms
are also quite close to one another (range, 2.894(7)-2.933(9)
Å); similarly, at the other end of the cavity, the distance between
any one ethereal O atom and the bridgehead N spans the range,
2.860(5)-2.919(7) Å. Thus, the molecule has a pseudo-3-fold
symmetry axis passing through the bridgehead nitrogens in the
solid state. Both the 1H- and 13C-NMR data are also consistent
with a 3-fold symmetry in the molecule in chloroform solution.
The distances and angles involving the bonded atoms of the
molecule lie within normal statistical values (Table 3).
[Cu(L)(CN)](picrate), 2. A perspective view of the molecule
giving the atom numbering scheme is shown in Figure 2. The
molecular structure consists of discrete [Cu(L)(CN)]+ cations
and picrate anions. The Cu(II) ion is coordinated to four N
atoms of the tren unit at one end of the cavity. The fifth
coordination site is occupied by a CN- group. The cavity above
the tren binding site undergoes reorganization upon binding of
the cyanide group. The top of the cavity is skewed away from
the metal center and the cyanide group. So, the pseudo-3-fold
symmetry present in L is lost, and the cyanide group resides
mostly outside the cavity. However, the ligand maintains the
endo-endo conformation where the two bridgehead N atoms
N(1)-C(1)-C(2)
N(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(3)-C(4)-C(9)
C(5)-C(4)-C(9)
C(4)-C(5)-C(6)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
O(1)-C(8)-C(7)
O(1)-C(8)-C(9)
C(7)-C(8)-C(9)
C(4)-C(9)-C(8)
110.8(9) N(1)-C(22)-C(21)
109.8(9) N(1)-C(23)-C(24)
122.3(9) N(5)-C(24)-C(23)
120.0(1) N(5)-C(25)-C(26)
118.1(8) C(25)-C(26)-C(27) 121.0(1)
121.0(1) C(25)-C(26)-C(31) 121.6(9)
121.0(1) C(27)-C(26)-C(31) 118.0(1)
118.0(9) C(26)-C(27)-C(28) 124.0(1)
122.3(8) O(3)-C(28)-C(27)
116.0(1) O(3)-C(28)-C(29)
121.0(1) C(27)-C(28)-C(29) 118.1(9)
121.0(1) C(28)-C(29)-C(30) 118.0(1)
117.0(1)
125.0(1)
O(1)-C(10)-C(11) 108.0(9) C(29)-C(30)-C(31) 123.0(1)
N(3)-C(11)-C(10) 110.7(8) C(26)-C(31)-C(30) 119.0(1)
N(3)-C(12)-C(13) 111.3(7) O(3)-C(32)-C(33)
O(2)-C(13)-C(12) 106.1(8) N(3)-C(33)-C(32)
107.0(9)
111.7(9)
units, as shown in Scheme 1. The condensation reaction goes
smoothly at the temperature range of 278-298 K without using
any templating metal ion. We have tried many solvents; the
mixed solvent system of THF + MeOH gives the best results.
The temperature for the reaction was kept at (278 ( 1 K) to
restrict the conformational degrees of freedom of the two
tripodal units. The high yield of the desired product shows that
it is thermodynamically very stable. The same cryptand can
be synthesized at elevated temperature (313 K) in presence of
Cs(I) as the templating ion in comparable yields. The tren end
of the cavity is well-suited to form inclusion complexes with
transition metal ions, and the presence of three meta-substituted
benzene rings makes the N donor atoms in L somewhat rigid.
The cryptand readily forms mononuclear complexes with the
Cu(II) ion when it is treated in one molar ratio with copper(II)
perchlorate hexahydrate or copper(II) picrate salts. The per-
chlorate complex was found to be very hygroscopoic, and we
did not proceed any further with this complex. The picrate
complex can be isolated in the solid state without any difficulty,
(20) Grey, W. J. Coord. Chem. ReV. 1971, 7, 81.
(21) Johnson, C. K. ORTEP. Report ORNL- 3794; Oak Ridge National
Laboratory: Oak Ridge, TN, 1971.

3384 Inorganic Chemistry, Vol. 35, No. 11, 1996
Chand and Bharadwaj
Table 4. Non-Hydrogen Positional and Equivalent Isotropic
Displacement Parameters (Å2) for {[Cu(CN)]L}(picrate) (2) (Esds in
parentheses)
atom
x/a
y/b
z/c
U(eq)
Cu
0.24559(5)
0.2377(4)
0.2406(4)
0.4332(3)
0.2503(4)
0.0905(3)
0.1904(3)
0.0111(3)
-0.0024(4)
0.1296(5)
0.2547(6)
0.3245(4)
0.3640(4)
0.2486(3)
0.3869(3)
0.2810(4)
0.2990(4)
0.0889(3)
0.0367(4)
0.1887(7)
0.3148(5)
0.3282(4)
0.4196(4)
0.4703(4)
0.5037(4)
0.5756(4)
0.6000(4)
0.5546(4)
0.4845(4)
0.4598(4)
0.4548(4)
0.3891(5)
0.2400(5)
0.1847(5)
0.2875(5)
0.2496(4)
0.2918(4)
0.3726(4)
0.4073(4)
0.3661(5)
0.2392(5)
0.295(1)
0.2710(5)
0.1455(4)
0.0632(4)
0.0089(4)
-0.0041(4)
0.0497(4)
0.0389(4)
-0.0260(5)
-0.0803(5)
-0.0695(4)
0.1703(5)
0.2212(5)
0.1827(4)
0.1120(5)
0.1153(5)
0.1829(6)
0.2471(5)
0.2455(5)
0.85770(6)
1.1110(5)
1.0174(5)
1.0317(4)
0.8434(5)
1.0204(4)
0.5742(4)
0.6783(5)
0.7363(5)
0.5248(6)
0.4118(6)
0.2966(5)
0.4468(5)
0.6961(4)
0.8740(4)
1.0716(4)
0.7599(40
0.8490(4)
0.6769(5)
0.4752(7)
0.3971(6)
0.6929(5)
0.7615(5)
0.9479(5)
0.9226(5)
0.8395(5)
0.8197(5)
0.8813(5)
0.9641(5)
0.9848(5)
1.0163(6)
1.0981(6)
1.0486(7)
0.9392(7)
0.7911(5)
0.8075(5)
0.7559(5)
0.6845(5)
0.6642(6)
0.7184(6)
0.7777(6)
0.6492(7)
0.6126(5)
0.6719(5)
0.7302(5)
0.9205(5)
0.9010(5)
0.9700(5)
0.9574(5)
0.8741(7)
0.8069(6)
0.8217(6)
1.0929(6)
1.1486(6)
0.5462(5)
0.5941(6)
0.5714(6)
0.4942(6)
0.4372(6)
0.4619(5)
0.28364(2)
0.2595(2)
0.2669(2)
0.1248(1)
-0.0226(2)
0.0963(1)
-0.1031(1)
-0.0844(2)
-0.0075(2)
0.1329(2)
0.1228(2)
-0.0563(2)
-0.0964(2)
0.3136(2)
0.3256(2)
0.0388(2)
0.2104(2)
0.3012(2)
-0.0395(2)
0.1060(30
-0.0649(2)
0.3560(2)
0.3409(2)
0.3069(2)
0.2515(2)
0.2397(2)
0.1888(2)
0.1491(2)
0.1604(2)
0.2114(2)
0.0721(2)
0.0406(2)
-0.0123(3)
-0.0192(2)
0.0217(2)
0.0704(2)
0.1129(2)
0.1059(2)
0.0564(2)
0.0144(2)
0.1632(2)
0.2251(3)
0.2724(3)
0.3363(2)
0.3042(20
0.2757(2)
0.2179(2)
0.1844(2)
0.1315(2)
0.1119(2)
0.1447(3)
0.1975(3)
0.1158(2)
0.0706(3)
-0.0575(2)
-0.0210(2)
0.0310(3)
0.0507(3)
0.0187(3)
-0.0329(2)
0.0352(2)
0.065(2)
0.042(2)
0.053(2)
0.089(2)
0.057(2)
0.063(2)
0.085(2)
0.117(3)
0.134(4)
0.140(4)
0.120(3)
0.124(30
0.039(2)
0.040(2)
0.049(2)
0.047(2)
0.044(2)
0.069(3)
0.099(4)
0.074(3)
0.052(2)
0.054(2)
0.045(2)
0.039(2)
0.051(2)
0.056(3)
0.052(2)
0.044(2)
0.040(2)
0.057(3)
0.064(3)
0.071(3)
0.068(3)
0.052(2)
0.050(2)
0.041(2)
0.052(2)
0.065(3)
0.056(3)
0.069(3)
0.193(7)
0.076(3)
0.053(2)
0.052(2)
0.050(2)
0.039(2)
0.040(2)
0.044(2)
0.062(3)
0.071(3)
0.062(3)
0.061(3)
0.075(3)
0.047(2)
0.054(3)
0.062(3)
0.069(3)
0.064(3)
0.051(2)
N(1a)
C(1a)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
N(7)
N(8)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
Figure 3. ORTEP21 drawing of the cation of 3 showing the thermal
ellipsoids and the atomic numbering scheme. Hydrogen atoms are
omitted for clarity.
N(4) bond length (2.339(6) Å) is appreciably long for a Cu-N
bond.22 The Cu-N(1) (bridgehead N)22 as well as the Cu-C
(CN-)23 bond distances are within the normal ranges. The long
Cu-N(4) distance is due to the ligand architecture which does
not allow the N(4) atom to come closer to the Cu(II) ion. We
propose that it is due to the presence of three meta-substituted
benzene rings which make the N donor atoms somewhat rigid.
The relationship of the Cu-N bond lengths in trigonal-
bipyramidal CuN4X complexes has been the subject of inves-
tigation by different groups.24 The Cu-C(1a)-N(1a) angle is
almost linear 175.9(5)°. The distance between the N atom of
the CN- group and N(3) is 5.761(7) Å.
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
[Cu(L)(NCS)](picrate), 3. A perspective view of the
molecule showing the atom numbering scheme is given in
Figure 3. The molecular structure consists of [Cu(L)(NCS)]+
cations and picrate anions. In this case, also, the cryptand has
an endo-endo conformation where the distance between the
two bridgehead N atoms is 8.225(5) Å, which is very similar
to that found in 2. As in the case of 2, the Cu(II) ion is
coordinated to four N atoms at the tren end of the cavity. The
fifth coordination site is occupied by the N atom of the SCN-
group. The coordination geometry around Cu(II) is quite similar
to that found in the case of 2. The Cu-N(4) bond distance
(2.384(5) Å) is again much longer than normal,22 whereas the
other Cu-N distances range within 1.939(5)-2.094(5) Å, the
length of the axial Cu-N(1a) bond being the lowest. The Cu(II)
ion is 0.230(4) Å above the plane described by the equatorially
bonded N(2), N(4), and N(5) atoms. The coordination geometry
around the Cu(II) ion is thus quite similar to that found in 2.
Upon binding of the thiocyanate group, the top of the cavity is
skewed away from the metal center more than that in case of
2. This has increased the nonbonding distance between N(3)
and S(1a) to 6.223(3) Å.
have come closer to each other by about 1.5 Å (distance 8.397(7)
Å) compared to that in the uncomplexed L. The coordination
geometry around the metal ion is close to trigonal bipyramidal,
where the bridgehead nitrogen N(1) and the atom C(1a) of the
cyanide occupy the axial positions. The metal ion is 0.278(4)
Å out of the trigonal plane described by the three secondary
amino N atoms (N(2), N(4), and N(5)) in the direction away
from the bridgehead atom N(1). Equatorial Cu-N bond lengths
are significantly longer than the axial one (Table 6). An
imporatnt fact about this structure is that the equatorial Cu-
(22) Baxter, C. E.; Rodig, O. R.; Schlatzer, R. K.; Sinn, E. Inorg. Chem.
1979, 18, 1918. Gouge, E. M.; Geldard, J. F.; Sinn, E. Inorg. Chem.
1980, 19, 3356. Patmore, D. J.; Rendle, D. F.; Storr, A.; Trotter, J. J.
Chem. Soc., Dalton Trans. 1975, 718.
(23) Anderson, O. P. Inorg. Chem. 1975, 14, 730.
(24) Deeth, R. J.; Gerloch, M. Inorg. Chem. 1984, 23, 3853. Addison, A.
W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem.
Soc., Dalton Trans. 1984, 1349.

A Heteroditopic Cryptand
Inorganic Chemistry, Vol. 35, No. 11, 1996 3385
Table 5. Non-Hydrogen Positional and Equivalent Isotropic
Displacement Parameters (Å2) for {[Cu(NCS)]L}(picrate) (3) (Esds
in parentheses)
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
{[Cu(CN)]L}(picrate) (2) and {[Cu(NCS)]L}(picrate) (3) (Esds in
Parentheses)
atom
x/a
y/b
z/c
U(eq)
2
3
Cu
0.59568(2)
0.62312(7)
0.6094(1)
0.6148(2)
0.6654(1)
0.7436(1)
0.70925(9)
0.54442(9)
0.5623(1)
0.5576(2)
0.4764(1)
0.4555(1)
0.4773(1)
0.5014(1)
0.5752(1)
0.5637(1)
0.7215(1)
0.6296(1)
0.6027(1)
0.5521(1)
0.4721(2)
0.4931(1)
0.5466(1)
0.5479(1)
0.5687(1)
0.5909(2)
0.5847(2)
0.6059(2)
0.6332(2)
0.6392(2)
0.6183(2)
0.6887(2)
0.7137(2)
0.7531(2)
0.7511(2)
0.7201(1)
0.6989(1)
0.6759(1)
0.6738(2)
0.6942(2)
0.7171(2)
0.6536(1)
0.6096(1)
0.5907(1)
0.5742(1)
0.6002(1)
0.6244(1)
0.6543(1)
0.6677(1)
0.6950(1)
0.7101(1)
0.6970(2)
0.6693(2)
0.6933(2)
0.7132(2)
0.5268(1)
0.5295(1)
0.5120(2)
0.4898(1)
0.4839(1)
0.5012(1)
0.83961(8)
0.6345(3)
0.7554(6)
0.7055(7)
1.1013(5)
1.1338(6)
0.7648(5)
0.6562(5)
0.4836(6)
0.2915(7)
0.1611(7)
0.2954(6)
0.7364(5)
0.8101(5)
0.9091(5)
0.9275(5)
1.0012(7)
0.9921(5)
0.6786(5)
0.4015(7)
0.2682(8)
0.7202(7)
0.9438(7)
1.0110(6)
0.9891(7)
1.0904(7)
1.2175(8)
1.3078(8)
1.2736(9)
1.1473(9)
1.0574(7)
1.1821(9)
1.114(1)
0.34814(4)
0.5875(1)
0.4461(3)
0.5049(4)
0.5366(3)
0.3861(3)
0.4345(3)
0.3362(2)
0.2340(3)
0.2701(4)
0..3896(4)
0.4656(4)
0.4613(3)
0.3699(4)
0.2469(3)
0.4055(3)
0.5251(4)
0.3165(3)
0.2792(3)
0.2770(4)
0.4162(4)
0.4081(4)
0.2679(4)
0.3482(4)
0.4848(3)
0.4879(4)
0.4711(4)
0.4738(4)
0.4935(5)
0.5128(4)
0.5093(4)
0.5326(5)
0.5686(6)
0.4160(5)
0.5019(5)
0.3377(4)
0.3300(4)
0.2775(4)
0.2346(4)
0.2450(5)
0.2962(5)
0.2685(4)
0.2813(4)
0.2170(4)
0.1873(3)
0.1959(3)
0.2966(4)
0.2973(4)
0.3672(3)
0.3700(4)
0.3028(5)
0.2340(4)
0.2303(4)
0.4982(4)
0.5556(4)
0.3466(3)
0.3243(4)
0.3462(4)
0.3905(4)
0.4100(4)
0.3871(3)
0.0382(3)
0.121(1)
0.049(2)
0.051(3)
0.081(2)
0.089(3)
0.060(2)
0.052(2)
0.089(3)
0.124(4)
0.102(3)
0.091(3)
0.073(2)
0.085(3)
0.041(2)
0.040(2)
0.075(3)
0.049(2)
0.042(2)
0.062(3)
0.071(3)
0.053(2)
0.050(3)
0.045(2)
0.049(3)
0.046(3)
0.058(3)
0.072(4)
0.068(3)
0.060(3)
0.049(3)
0.090(4)
0.100(5)
0.078(4)
0.086(4)
0.057(3)
0.053(3)
0.046(3)
0.061(3)
0.071(3)
0.062(3)
0.054(3)
0.053(3)
0.049(3)
0.051(3)
0.051(3)
0.049(3)
0.044(2)
0.047(2)
0.048(3)
0.063(3)
0.064(3)
0.058(3)
0.066(3)
0.082(4)
0.041(2)
0.045(3)
0.056(3)
0.049(3)
0.048(3)
0.042(2)
Bond Lengths
2.055(5)
S(1a)
N(1a)
C(1a)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
N(7)
N(8)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
Cu-N(1)
Cu-N(2)
Cu-N(4)
Cu-N(5)
Cu-C(1a)
Cu-N(1a)
2.058(5)
2.094(5)
2.384(5)
2.067(5)
2.134(5)
2.339(6)
2.114(5)
1.942(6)
1.939(5)
Bond Angles
83.4(4)
N(1)-Cu-N(2)
N(1)-Cu-N(4)
N(1)-Cu-N(5)
N(2)-Cu-N(4)
N(2)-Cu-N(5)
N(4)-Cu-N(5)
C(1a)-Cu-N(1)
C(1a)-Cu-N(2)
C(1a)-Cu-N(4)
C(1a)-Cu-N(5)
Cu-C(1a)-N(1a)
N(1a)-Cu-N(1)
N(1a)-Cu-N(2)
N(1a)-Cu-N(4)
N(1a)-Cu-N(5)
Cu-N(1a)-C(1a)
84.2(2)
81.7(2)
84.9(2)
109.1(3)
140.9(2)
105.3(3)
80.8(5)
83.4(4)
100.5(5)
136.9(4)
117.2(8)
170.8(2)
92.8(3)
108.1(5)
93.8(4)
175.9(5)
171.0(2)
91.1(2)
107.2(3)
94.1(2)
173.3(6)
Table 7. Selected Nonbonded Distances (Å) for L,
{[Cu(CN)]L}(picrate) (2) and {[Cu(NCS)]L}(picrate) (3)
L
2
3
C(7)
C(8)
C(9)
N(1)‚‚‚N(3)
N(2)‚‚‚N(4)
N(2)‚‚‚N(5)
N(4)‚‚‚N(5)
N(1)‚‚‚N(2)
N(1)‚‚‚N(4)
N(1)‚‚‚N(5)
O(1)‚‚‚O(2)
O(1)‚‚‚O(3)
O(2)‚‚‚O(3)
N(3)‚‚‚O(1)
N(3)‚‚‚O(2)
N(3)‚‚‚O(3)
C(9)‚‚‚C(15)
C(9)‚‚‚C(27)
C(15)‚‚‚C(27)
9.904(7)
3.738(7)
3.684(7)
3.717(9)
2.923(6)
2.894(7)
2.933(9)
3.672(6)
3.579(5)
3.520(7)
2.919(7)
2.873(7)
2.860(5)
4.09(1)
8.397(7)
3.445(6)
3.951(6)
3.804(6)
2.793(6)
2.862(6)
2.779(6)
4.982(6)
4.535(6)
4.302(6)
2.990(6)
3.156(7)
2.993(6)
4.984(8)
5.406(7)
4.424(8)
8.225(5)
3.551(2)
3.922(1)
3.555(1)
2.782(2)
2.915(5)
2.785(2)
4.582(5)
4.505(4)
4.298(9)
2.903(7)
2.985(2)
2.949(2)
5.071(6)
5.339(4)
4.350(2)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
1.0079(8)
1.000(1)
1.1451(8)
1.0551(7)
1.0734(7)
1.1872(8)
1.2791(8)
1.2583(8)
0.9708(7)
1.0856(7)
1.0216(7)
0.8036(7)
0.7229(7)
0.5800(6)
0.6243(6)
0.6711(7)
0.7113(7)
0.6998(8)
0.6538(8)
0.6165(7)
0.8023(8)
0.8795(9)
0.5722(7)
0.4397(7)
0.3434(7)
0.3719(7)
0.4963(8)
0.5919(7)
4.022(8)
4.00(1)
Spectral and Magnetic Studies. In the UV-vis-near-IR
spectral studies, 1-4 show two broad ligand field bands in the
region, 9500-16 000 cm-1. At energies higher than 22 000
cm-1, the picrate anion shows intense absorption25 obscuring
LMCT transitions involving the metal ion and the ligating donor
atoms. At energies lower that 7200 cm-1, sharp peaks due to
vibrational overtones appear. Spectra in the solid state, though
not well-resolved, indicate that the complex ions retain their
identity in solutions. The ligand field bands do not change shape
or position upon changing the solvent from MeCN to DMF.
For a regular trigonal-bipyramidal Cu(II) complex, usually two
ligand field bands appear26 in the region, 9500-16 000 cm-1
with greater absorption intensity for the lower energy transition,
although exceptions27 to this general observation are known.
The general shape and band positions (Table 8) in the spectra
of 2-4, are quite similar to those observed for trigonal-
The nonbonding distances between the three equatorially
coordinated N atoms are similar in 2 as well as in 3 and are
slightly different compared to the corresponding distances found
in L (Table 7). A comparison of the structures of 2 and 3 with
that of L reveals that the tren end is quite rigid and the N donor
atoms at this end do not move tremendously upon metal binding.
In another words, the donor atoms enforce the distorted
coordination geometry on to the Cu(II) ion in both of the
structures.
(25) Takemura, H.; Shinmyozu, T.; Inazu, T. J. Am. Chem. Soc. 1991, 113,
1323.
(26) Hathaway, B. J.; Billing, D. E. Coord. Chem. ReV. 1970, 5, 143.
Dudley, R. J.; Hathaway, B. J.; Hodgson, P. G.; Power, P. C.; Loose,
D. J. J. Chem. Soc., Dalton Trans. 1974, 1005.
(27) Addison, A. W.; Hendriks, H. M. J.; Reedijk, J.; Thompson, L. K.
Inorg. Chem. 1981, 20, 103.

3386 Inorganic Chemistry, Vol. 35, No. 11, 1996
Chand and Bharadwaj
Table 8. Ligand Field Bands (cm-1) and Magnetic and EPR Spectral Data for 1-4
b
compound
d-da
µ/µB
gII
g
AII (×104 cm-1
)
ref
1
2
3
4
9500(95)
11000(115)
14200(210)
11400(145)
15100(215)
1.94
2.07(gav)c
2.14d
this work
2.06
2.05
60
91
2.18e
2.01
1.98
2.03
2.09(gav)c
2.03d
this work
this work
this work
2.12
2.21
65
70
2.03e
11300(150)
14800(180)
2.08(gav)c
2.04d
2.14
2.24
70
75
2.03e
11400(170)
15200(220)
2.06(gav)c
2.03
2.13
2.21
2.21
70
85
69
2.02
2.00
[Cu(NTB)(N3)]1+
9700(119)
13150(100)
9500(212)
12500(235)
27
27
[Cu(NTB)(NCS)]1+
2.01
2.22
69
[Cu(tren)(OH)]1+
[Cu(tren)Br]Br
2.00
2.00
2.21
2.21
68
67
28
28
11200
13800
11400
15200
[Cu(tren)(NH3)]2+
2.21
2.18
84
28
a Electronic spectra of 1-4 at 298 K in MeCN; molar extinction coefficient is in parentheses. b 298 K. c Solid sample at 298 K. d In MeCN at
298 K. e In MeCN at 77 K.
bipyramidal [Cu(tren)X]n+ (X ) Br-, NH3; n ) 1,2)28 and
[Cu(NTB)X]1+ (NTB ) tris(2-benzimidazolylmethyl)amine; X
) SCN- and N3- 27 complexes. For 1, which will be tetraco-
)
ordinated with ligation from four N donors of L, the ligand
field bands are slightly red-shifted and three bands can be
located (Table 8). We have seen that the cryptand enforces a
distorted trigonal-pyramidal geometry onto the Cu(II) ion in both
2 and 3. It is quite reasonable to assume that in 1, also, the
coordination geometry around Cu(II) will be distorted trigonal
pyramidal. Therefore, we propose that the ligand field bands
in 1 correspond to a distorted trigonal-pyramidal CuN4 chro-
mophore which is unique in the literature. However, it is
possible that MeCN or DMF might be weakly coordinated to
the metal ion in 1.
Figure 4. EPR spectra of 1 in MeCN at 298 K (top) and at 77 K
The effective magnetic moment values for 1-4 lie within
1.94-2.03 µB at 298 K, which are well within the normal range
observed29 for discrete Cu(II) complexes. The EPR spectral
data of the complexes are collected in Table 8. Complex 1
displays interesting EPR spectral characteristics. It shows a
broad signal with gav ) 2.07 in the solid state at 298 K, which
sharpens somewhat on cooling to 77 K. Thus, the pure solid
sample is not magnetically dilute to exhibit resolved EPR
spectrum indicative of its stereochemistry. However, in MeCN
solution at 298 K, it shows an axial spectrum (Figure 4).
Changing the solvent to CHCl3, which is less coordinating, gives
an identical spectrum. The gII value of 2.14 obtained with 1 is
smaller compared to typical pseudotetrahedral CuN4 complexes,
where the gII values have been found30 to be equal to or above
2.24. If we can assume that in 1 the four N donors impose a
geometry similar to that in 2 and 3, then this geometry will be
distorted trigonal pyramidal, where the Cu(II) ion will be above
the equatorial plane and away from the bridgehead N atom.
Also, one of the equatorial bonds will be appreciably longer
(like Cu-N(4) bond in 2 and 3) leading to a low ligand field
strength. In MeCN glass (77 K), the signal is still axial (Figure
4), and the g values change slightly. This is attributable to the
conformational changes in the ligand superstructure upon
(bottom).
cooling, which will enforce changes in the coordination
geometry or to the solvent coordination at low temperature.
Complexes 2-4 show broad signals near g ) 2.05 in the solid
state at 298 or 77 K. In MeCN each exhibits a significantly
rhombic signal (Table 8) at 298 K, which sharpens at 77 K.
The g and A values are quite different from those obtained in
1 and agrees well with trigonal-bipyramidal [Cu(NTB)X]1+ (X
- 27
28
) NCS- and N3
complexes.
)
and [Cu(tren)(OH)]1+ and Cu(tren)Br2
Electrochemistry. Electron transfer properties of the com-
plexes were probed by cyclic voltammetry at 298 K on
dinitrogen flushed solutions in MeCN. None of the complexes
show any cyclic responses in the region, +1.0 to -1.0 V. Only
ill-defined peaks are found in the forward scans which disappear
in the reverse scans. Rigidity of the N4-donor set does not allow
its spatial rearrangements upon reduction/oxidation of the
metal-ligand ensemble, leading to irreversibility of the cyclic
redox processes.
Conclusion. The three meta-substituted benzene rings
present in the cryptand L makes the donor atoms somewhat
rigid in nature. Therefore, the cryptand can enforce a distorted
trigonal-pyramidal geometry onto the Cu(II) ion. When the fifth
coordination site is empty, the geometry around the Cu(II) ion
becomes distorted trigonal pyramidal. This gives an interesting
EPR spectrum. Once the crystal structure of 1 is available, the
preorganization of the ligand structure and the spectral char-
(28) Duggan, M.; Ray, N.; Hathaway, B.; Tomilnson, G.; Brint, P.; Peein,
K. J. Chem. Soc., Dalton Trans. 1980, 1342.
(29) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed;
Wiley: New York, 1988; p 768.
(30) Knapp, S.; Keenan, T. P.; Zhang, X.; Fikar, R.; Potenza, J. A.; Schugar,
H. J. J. Am. Chem. Soc. 1990, 112, 3452, and references cited therein.

A Heteroditopic Cryptand
Inorganic Chemistry, Vol. 35, No. 11, 1996 3387
acteristics of 1 can be probed quantitatively. To test the rigidity
of the binding site, it is also important to have Ni(II) or Pt(II)
cryptates with L. Efforts are on to reach these goals.
istry, IIT Kanpur. P.K.B. wishes to acknowledge the DST for
funding this facility.
Supporting Information Available: Tables of crystallographic
data, hydrogen positional parameters, anisotropic thermal factors for
L, 2, and 3 and all of the bond distances and angles for 2 and 3 and
figures of the packing diagrams for L, 2, and 3 (16 pages). Ordering
information is given on any current masthead page.
Acknowledgment. Financial support by the Department of
Science and Technology (DST), New Delhi, India, is gratefully
acknowledged. X-ray structural studies were made at the
National X-ray Crystallographic Facility, Department of Chem-
IC950933+