Chiral copper(I) iodide based porous coordination frameworks with asymmetrically substituted bridging N-donor ligands

Article abstract of DOI:10.1515/znb-2000-0604

The 2-dimensional coordination polymers ²_∞[{(CuI)₂(Mepyz)₂} · Mepyz] (1a), ²_∞[CuX(Mepyz)] (2a, X = Br; 2b, X = Cl) and ²_∞[(CuX)₂(Mepyz)] (3a, X = I;3b, X = Br) may be prepared by reaction of the appropriate copper(I) halide with 2-methylpyrazine (Mepyz) either in acetonitrile solution at 130 °C (2a/2b, 3a/3b) or without solvent at 20 °C (1a). Mepyz ligands bridge (CuI)₂ rhomboid dimers in the chiral network of 1a, whose resulting 24-membered rings are large enough to accomodate an Mepyz guest molecule. 1a rapidly loses these guests to afford a crystalline powder (1b), that can reversibly imbibe benzonitrile molecules into its open channels. In contrast to 1a, the sheets of 2a/2b contain zigzag infinite CuX chains, those of 3a/3b staircase ¹_∞[CuX] double chains as their characteristic substructures. Helical ¹_∞[CuI] single chains in the 3-dimensional network of ³_∞[CuI(Mepip)]4 are bridged by R-2-methylpiperazine (Mepip) ligands in a second example of a chiral coordination polymer.

Full text of DOI:10.1515/znb-2000-0604

Chiral Copper(I) Iodide Based Porous Coordination Frameworks
with Asymmetrically Substituted Bridging N-Donor Ligands
B. Roßenbeck and W. S. Sheldrick
Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
Reprint requests to Prof Dr. W. S. Sheldrick. E-mail: shel@anachem.ruhr-uni-bochum.de
Z. Naturforsch. 55 b, 467^472 (2000); received February 1, 2000
Copper(I) Halides, 2-Methylpyrazine, Chiral Network
The 2-dimensional coordination polymers 2.[{(CuI)2(Mepyz)2} •Mepyz] (la), (2)[CuX(Me-
pyz)] (2a, X = Br; 2b, X = Cl) and ^[(CuX^M epyz)] (3a, X = I;3b, X = Br) may be
prepared by reaction of the appropriate copper(I) halide with 2-methylpyrazine (Mepyz) either
in acetonitrile solution at 130 °C (2a/2b, 3a/3b) or without solvent at 20 °C (la). Mepyz ligands
bridge (Culh rhomboid dimers in the chiral network of la, whose resulting 24-membered
rings are large enough to accomodate an Mepyz guest molecule, la rapidly loses these guests
to afford a crystalline powder (lb), that can reversibly imbibe benzonitrile molecules into its
open channels. In contrast to la, the sheets of 2a/2b contain zigzag infinite CuX chains, those
of 3a/3b staircase ^[CuX] double chains as their characteristic substructures. Helical JJCul]
single chains in the 3-dimensional network of ^[CuLM epip)^ are bridged by R-2-methyl-
piperazine (Mepip) ligands in a second example of chiral coordination polymer.
Introduction
both chiral and porous. The asymmetric bridg-
ing heterocyclic diazines, whose 2-methyl sub-
stituents protrude into the large nanometer-sized
channels of c^[CuCN(//-2M epyz)] (dimensions
1.10 x 1.14 nm), are clearly instrumental in inducing
the adoption of a chiral framework during the self-
assembly process. As such porous networks could
be of potential interest for both asymmetric catal-
ysis and nonlinear optics we considered it to be
of interest to establish whether similar copper(I)
halide based polymers can be obtained. Many types
of oligomeric and polymeric CuX (X = Cl, Br, I)
substructures have been found in their coordina-
tion frameworks with bridging spacer molecules,
for instance (CuX)2 rings, cubane-like and tricyclic
CU4X4 tetramers, zigzag ,4 [CuX] single chains
and staircase or spirocyclic ^[C uX ] double chains
[1 8 -2 2 ]. Both 2-methylpyrazine and the chiral
derivative R-2-methylpiperazine (Mepip) were em -
ployed as asymmetrically substituted N-donor lig-
ands in the present work.
Two ever recurring goals in the rapidly expand-
ing field of inorganic crystal engineering are the
development of functional materials with zeolite-
like molecular-sized cavities or channels f1 - 4] and
the construction of chiral coordination networks of
potential utility for nonlinear optics [5]. However,
attempts to design two- or three-dimensional frame-
works with larger well-defined pores have often
been foiled by the self-interpenetration of multiple
networks, which eliminates the void space [6]. This
phenomenon is particularly typical for diamondoid
polymers [3], for which as many as eight or nine
interweaving frameworks can be obtained [7 - 9].
As a result, surprisingly few coordination frame-
works have been reported that can clathrate organic
guest molecules with a degree of shape specificity
[10 - 16]. Several of these examples contain biden-
tate rodlike 4,4'-bipyridine as an organic spacer
molecule, and tridentate ligands have also been suc-
cessfully employed to construct such porous mate-
rials [11, 15],
Results and Discussion
We ourselves have recently described the assem-
bly of two CuCN based three-dimensional frame-
works ^[CuCN(/z-2M epyz)] and ^[C uC N (//-4M e-
pym)] (2Mepyz = 2-methylpyrazine, 4Mepym =
4-methylpyrimidine) [17], the former of which is
Treatment of Cul with an equimolar quantity
of the liquid 2-methylpyrazine at room tempe-
rature leads to slow growth of orange crys-
tals of the chiral lamellar coordination poly-
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468
B. Roßenbeck and W. S. Sheldrick • Chiral Copper(I) Iodide Based Porous Coordination Frameworks
Fig. 1. Asymmetric unit of the <2,[(CuI)2(Mepyz)2] sheets
of la. Selected bond lengths (A) and angles (°): Cu(l)-
1(1) 2.659(3), Cu(l)-I(2) 2.737(3), Cu(2)-I(l) 2.619(3),
Cu(2)-I(2) 2.575(3), Cu(l)-I(l)-Cu(2) 63.27(9), Cu(2)-
I(2)-Cu(l) 62.74(9), I( 1)-Cu( 1)-I(2) 111.86(9), 1(1)-
Cu(2)-I(2) 118.79(9).
mer ^ [{ (C u I^ M e p y z ^ } • Mepyz] la (space
group P2\2\2\), which contains (Cul)2 rings as
its characteristic building blocks. In contrast,
c2![CuX(Mepyz)] (X = Br, Cl; 2a, 2b) and ^[(C u X )2
(Mepyz)] (X = I, Br; 3a, 3b), which were prepared
by reacting the appropriate copper (I) halide with
2-methylpyrazine at the required molar ratio in ace-
tonitrile solution (T = 130 °C), all crystallise in
the centrosymmetric monoclinic space group P2\lc
and exhibit respectively single and double chains as
component CuX substructures.
2-Methylpyrazine ligands bridge the (Cul)2
rhomboid dimers through N (ll)-C u (l) and N(41)-
Cu(2) bonds (Fig. 1) to afford an open 44 net with
large 24-membered rings. Neighbouring sheets at
an average distance of 6.96 A (b/2) are related by
21 screw diad axes and stack so as to create con-
tinuous channels whose dimensions (8.74x8.54 A
cross section) are large enough to accomodate a
noncoordinated 2-methylpyrazine guest molecule.
As may be seen in Fig. 2a), Einer jj(C u I)2(Me-
pyz)] chains in direction [100] are connected by
2-methylpyrazine pillars in direction [001], which
themselves belong to Zweier chains of the same
composition. The presence of differing k 2N\ and
Fig. 2. a) Projection of the structure of 2.[CuI)2(Mepyz)2]
la with its Mepyz guests perpendicular to [010], and
b) Stacking of the polymeric sheets of la as viewed
along [100].
k2N4 coordination modes at the independent cop-
per atoms C u(l) and Cu(2) is also reflected in a
marked distortion of the (Cul)2 lozenges. Longer
C u(l)-I distances of 2.659(3) and 2.737(3) A ac-
company the shorter C u(l)-N (l 1) and Cu(l)-N(12)
bonds [2.05(1) A]. In contrast Cu(2)-I bond lengths
of 2.619(3) and 2.575(3) A are associated with the
longer Cu(2)-N distances to the 2-methylpyrazine
N4 atoms [2.09(1), 2.07(2) A], A Cu(l)...C u(2) sep-
aration of 2.769(3) A is observed within the (Cul)2
rings. The stacking of ^ [(C u I^ M e p y z ^ ] layers in
la is illustrated by Fig. 2b), which also shows how
individual (Cul)2 rings in neighbouring sheets inter-
act through weak secondary 1(1)...1(2) interactions.
It is also apparent from this projection of the struc-
ture that the 2-methylpyrazine guest molecules are
significantly displaced from the sheets of the host-
ing 2-dimensional coordination polymers.
1:1 CuBr and CuCl based coordination poly-
mers of 2-methylpyrazine could only be obtained
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469
B. Roßenbeck and W. S. Sheldrick • Chiral Copper(I) Iodide Based Porous Coordination Frameworks
Fig. 3. Projection of the struc-
tures of ^ [CuX(Mepyz)] 2a and
2b (X=Br, Cl) with number-
ing for the former perpendic-
ular to [001]. Selected bond
lengths (A) and angles (°):
in 2a, Cu(l)-Br(l) 2.591(1),
Cu(l)-Br(la) 2.507(1), N(l)-
Cu(l)-N(4a) 137.3(1) in 2b,
Cu(l)-Cl(l) 2.484(1), Cu(l)-
Cl(l a) 2.378(1), N(l)-Cu(l)-
N(4a) 136.0(1).
Fig. 4. Projection of the structure of ^ [(CuI)2(Mepyz)] 3a
perpendicular to [001]. Selected bond lengths (A): Cu(l)-
1(1) 2.662(1), Cu(l)-I(lb)2.629(l),Cu(l)-I(lc) 2.722(1),
Cu(2)-I(2) 2.668(1), Cu(2)-I(2b) 2.642(1), Cu(2)-I(2c)
2.656(1).
Fig. 5. Framework structure of 3-,[CuI(Mepip)] 4 pro-
jected perpendicular to [100], Selected bond lengths (A)
and angles (°): Cu( 1)-I( 1) 2.783(2), Cu( 1)-I( 1a) 2.905(2),
Cu( 1)-N( 1) 2.056(8), Cu( 1)-N(4a) 2.068(9), N( 1)-Cu( 1)-
N(4a) 135.5(3).
from acetonitrile solution at higher temperature
(130 °C). In contrast to la, the isostructural com-
pounds (2.[CuX(Mepyz)] 2a and 2b (X = Br, Cl)
contain infinite zigzag CuX chains as their charac-
teristic copper(I) halide substructures. As depicted
in Fig. 3, such J-JCuX] ribbons are linked through
/i-N\,N4 coordinated 2-methylpyrazine spacers to
afford 2-dimensional polymers with 14-membered
pores. Neighbouring sheets are related through the
c glide planes of the monoclinic space group P2\/c
and stack so as to afford narrow channels in direc-
tion [001]. Particularly striking are the very wide
N (l)-C u(l)-N (4a) angles of 137.3(1) and 136.0(1)°
within the component c^[{Cu(M epyz)}+] ribbons
of 2a and 2b.
2:1 coordination polymers ^[(C u X ^M ep y z)]
3a and 3b (X = I, Br) could be isolated for Cul and
CuBr under similar reaction conditions but not for
the analogous copper(I) chloride. These compounds
also crystallise in the monoclinic space group P2\/c
but now contain ^[C uX ] staircase double chains,
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B. Roßenbeck and W. S. Sheldrick • Chiral Copper(I) Iodide Based Porous Coordination Frameworks
470
(b)
(a)
Fig. 6. Powder dia-
grams (Cu-Ka, Bruker
AXS D8 Advance):
(a) of c2[{(CuI)2(Me-
pyz)2} ■Mepyz], la; (b)
of J,[(CuI)2(Mepyz)2],
lb, as obtained after
removal of the guest
Mepyz molecules of la
under vacuum.
which are depicted in Fig. 4 for 3a. In contrast to integrity on loss or exchange of imbibed aromatic
2a/b, such CuX substructures in the 2:1 polymers molecules [10]. More typical are reports on ion ex-
are generated by the screw diads parallel to y, which change or replacement of smaller solvent molecules
therefore exhibits short repeat distances of respec- (e. g. s H2O, CH3CN, DMF) in the channels of such
tively 4.228(1) and 3.996(1) A in 3a/b. Cu-I and microporous networks [15].
Cu-Br distances within the double chains lie in the
narrow ranges 2.629 - 2.722 and 2.489 - 2.540 A.
Yellow ^[{(C uI^M epyz^} • Mepyz] (la) rap-
idly loses its 2 -methylpyrazine guest molecules un-
The crystallisation of ^[{(C uI^M epyz^} •Me- der vacuum at room temperature to afford an or-
pyz] la in the chiral orthorhombic space group
P2 j2 i2 i is in accordance with our previous ob-
servations for ^[CuCN(^-Mepyz)] (space group
P2\2\2\) and ^ [CuSCN(Mepym-K/Vl)] (space
group P I) [17], that asymmetrically substituted het-
erocyclic diazines can induce chirality into coordi-
nation polymers generated under kinetically con-
trolled self-assembly conditions. An alternative ap-
proach to this goal is to employ a chiral bridg-
ing ligand such as R-2-methylpiperazine (Mepip),
which generates a three-dimensional framework
^[CuKMepip)] 4 with Cul in acetonitrile at room
temperature. As may be seen in Fig. 5 helical
^[C ul] chains in direction [1 0 0 ] (space group
7^212 121) are linked together by bridging R-2-meth-
ylpiperazine molecules in 4 to afford narrow chan-
nels into which the 2 -methyl substituents protrude.
Alternating rather long Cu-I distances of 2.783(2)
and 2.905(2) A are observed within the infinite Cul
ribbons and are associated with wide N(l)-Cu(l)-
N(4a) angles of 135.5(3)°, similar to those found in
2a/b
ange microcrystalline powder (lb), whose elemen-
tal analysis is in accordance with a formulation as
[CuI(Mepyz)]. A powder diffraction pattern of (lb)
[Fig. 6 (b)] recorded with Cu-KQradiation confirms
the retention of crystallinity and contains strong
Bragg reflections in the 29 range 10 - 30° at angles
closely similar to those found for la [Fig. 6 (a)].
On covering lb with benzonitrile a colour change
from orange back to the original yellow can be
followed over a period of days. An IR spectrum
taken for the yellow powder after 7d contains char-
acteristic absorption bands for benzonitrile (e. g.
i/(CN), 2226 cm-1), thereby confirming success-
ful imbibement of this aromatic molecule. After re-
moval of benzonitrile under vacuum, the powder
diffraction pattern of the resulting yellow powder
once again closely resembles that of lb. A thermal
gravimetric analysis on la reveals that following
rapid loss its 2 -methylpyrazine guests, the coordi-
nation polymer lb is stable up to 210 °C before
endothermically losing both its bridging N-donor
ligands. Our results, therefore, suggest that after
removal of the Mepyz guest molecules, the host lat-
tice of ^[{(CuI)2 (Mepyz)2 } • Mepyz] la is able to
reversibly imbibe benzonitrile without loss of in-
tegrity.
Loss and Exchange of Guest Species by 1
Few examples of coordination frameworks have
been described that are capable of retaining their
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471
B. Roßenbeck and W. S. Sheldrick • Chiral Copper(I) Iodide Based Porous Coordination Frameworks
Table 1. Crystal and refinement data for 1 - 4 .
Compound
la
2a
2b
3a
3b
4
Formula
M
C15H18Cu2I2N6 C5H6BrCuN2
C5H6C1CuN2
193.1
C5H6Cu2I2N2
475.0
C5H6Br2Cu2N2 C5H,0CulN2
663.2
237.6
381.0
288.6
P2\2\2\
7.249(2)
9.090(2)
12.132(3)
90
P2\lc
P2\lc
P2\/c
Space group
P2\2\2\
8.740(3)
13.920(7)
17.082(5)
90
P2\/c
4.023(1)
12.940(4)
12.801(4)
96.83(2)
661.6(3)
4
3.861(1)
12.887(3)
12.585(3)
95.59(2)
623.2(2)
4
15.255(5)
4.228(1)
16.142(4)
112.23(2)
963.7(4)
4
15.066(3)
3.996(1)
15.619(3)
110.78(2)
879.2(3)
4
a
[A]
b [A]
c [ A]
ß [°]
V [A3]
Z
799.4(4)
4
2078.2(1)
4
2.398
2.120
2.385
2.058
3.274
2.879
Dcaic [g-cm-3 ]
544
F(000)
1256
456
384
856
712
0.32x0.22x0.18
Crystal size [mm] 0.18x0.16x0.12 0.62x0.32x0.24
0.32x0.12x0.02
0.66x0.20x0.18 0.42x0.18x0.16
9.24
6.51
;/(Mo-Ka)[mm_ 1] 5.03
3.82
10.76
13.86
Max./min. trans.
0.34/0.20
0.79/0.21
0.53/0.21
0.37/0.19
0.31/0.23
0.45/0.42
0,19/0,5/-20,18 0,9/0,11/0,15
hA/l Ranges
2#range [°]
0,10/0,16/0,20
4-50
0,5/-18,0/-17,17 0,5/0,16/-16,16 -19,18/0,5/0,20
4 - 60
4-55
4-55
4-55
4-55
1073
0.040
0.107
1.128
Independent refls
R\ [/ > 2cr(I)]
h7?2 [all data]
S [goodness-of-fit]
Min./max. res.
[e -A -3]
2097
0.055
0.125
1.024
1916
0.032
0.074
1.036
1419
0.040
0.104
1.214
2220
0.037
0.106
1.119
1992
0.095
0.270
0.957
1.29/-0.80
0.65/-0.62
3.44/-2.16
0.75/-1.30
0.69/-1.55
0.85/-1.73
Experimental
£,[CuCl(Mepyz)] (2b)
A 56% yield (120 mg) of red crystals of 2b was
achieved under conditions similar to 2a with 112 mg CuCl
(1.1 mmol) and 103 mg 2-methylpyrazine (1.1 mmol).
C5H6C1CuN2 (M = 193.1): Calcd C 31.1, H 3.1, N 14.5,
Cu 32.9. Found C 30.2, H 3.1, N 14.1, Cu 32.4%.
FTIR: KBr discs, Perkin Elmer 1760X; elemental anal-
ysis: VarioEL (Elementar Analysensystem GmbH) für C,
H, and N, AAS6 vario atom absorption spectrometer (Carl
Zeiss Technology) for Cu. The thermogravimetric analy-
sis (TGA/DTA) was performed on an Exstar 6000 (Seiko
Instruments), the PXRD study on a Bruker AXS D8 Ad-
vance. Syntheses of 2a, 2b, 3a and 3b were performed in
sealed glass tubes using dried acetonitrile as solvent.
£>[(CuI)2(Mepyz)] (3a)
Reaction of 191 mg Cul (1 mmol) and 68 mg 2-meth-
ylpyrazine (0.5 mmol) under conditions as for 2a afforded
yellow needles of 4 in 52% yield (123 mg). C5H6Cu2I2N2
(M = 475.0): Calcd C 12.6, H 1.3, N 5.9. Found C 13.0,
H 1.3, N 5.9%.
£ [{ (Culh(Mepyzh }•Mepyz] (la)
138
mg Cul (0.7 mmol) and 66 mg (0.7 mmol) 2-meth-
ylpyrazine (Mepyz) were mixed together and allowed
to stand at room temperature to afford orange crystals
of 1 in 91% yield (139 mg) over a period of 3 days.
C15Hi8Cu2I2N6, (M = 663.2): Calcd C 27.0, H 2.7, N
12.6%. Found C 27.3, H 2.9, N 12.9%.
£,[(CuBr)2(Mepyz)] (3b)
A 42% yield (206 mg) of orange crystals of 3b was ob-
tained by treating 373 mg CuBr (2.6 mmol) with 121 mg
2-methylpyrazine (1.3 mmol) under analogous reaction
conditions to 2a. CsH6Br2Cu2N2 (M = 381.0): Calcd C
15.9, H 1.6, N 7.4. Found C 15.6, H 1.6, N 7.3%.
^[CuBr(Mepyz)] (2a)
^[CuI(Mepip)] (4)
192 mg CuBr (1.34 mmol) and 122 mg 2-methylpyr-
azine (1.34 mmol) were heated in 1.5 ml CH3CN at 130 °C
for 40 h in a sealed glass tube. Slow cooling to room
191 mg Cul (1 mmol) and 98 mg R-2-methylpiper-
azine (Mepip) were added to 1.5 ml acetonitrile and the
temperature over 80 h afforded red needles of 2 in 66% reaction mixture left to stand for 8 d at room tempera-
yield (209 mg). C5H6BrCuN2(M = 237.6): Calcd C 25.3,
H 2.4, N 11.8, Cu 26.7. Found C 24.9, H 2.4, N 11.8, Cu
27.2%.
ture to afford yellow-brown crystals of 4 in 46% yield
(132 mg). C5Hi0CuIN2(M = 288.6): Calcd C 20.8, H 3.5,
N 9.7, Cu 22.0. Found C 20.1, H 4.1, N 9.0, Cu 22.1%.
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472
B. Roßenbeck and W. S. Sheldrick • Chiral Copper(I) Iodide Based Porous Coordination Frameworks
X-ray structural analyses of 1 -4
collection; significant deviations in intensity were not ob-
served. Semi-empirical absorption corrections were per-
formed on the basis of i/> scans for 9 chosen reflections
with high \ values. After structure solution with SHELXL
86, positional parameters and anisotropic temperature
factors were refined against F02 with SHELXL 93 [23].
Hydrogen atoms were included at calculated sites together
with group isotropic temperature factors. Absolute struc-
Crystal and refinement data for compounds 1 - 4 are
listed in Table 1. The X-ray structural analysis for 3b was
of poor quality and this compound, which is isostruc-
tural to 3a, is only included for comparison purposes.
Unit cell constants were obtained from least-squares fits
to the settings of 25 - 30 reflections centered on a Siemens
P4 diffractometer. Intensity data were collected in the u> tures of the chiral coordination polymers la and 4 were
assigned on the basis of their Flack parameters [24], which
refined to respectively 0.05(10) and -0.03(9) [25].
mode at 293 K. Three selected reflections were moni-
tored for each of the compounds during the course of data
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