Self-assembly through hydrogen-bonding and C-H?π interactions in metal complexes of N-functionalised glycine

Article abstract of DOI:10.1016/j.inoche.2006.07.038

The complex [Ni(L1)₂(py)₂]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas co-crystals having composition 2[Ni(L1)₂(py)₃(H₂O)] · [Ni(L1)₂

Full text of DOI:10.1016/j.inoche.2006.07.038

Inorganic Chemistry Communications 9 (2006) 1251–1254
www.elsevier.com/locate/inoche
Self-assembly through hydrogen-bonding and C–Hꢀ ꢀ ꢀp interactions
in metal complexes of N-functionalised glycine
*
Nilotpal Barooah, Anirban Karmakar, Rupam J. Sarma, Jubaraj B. Baruah
Department of Chemistry, Indian Institute of Technology, North Guwahati, Guwahati, Assam 781 039, India
Received 16 July 2006; accepted 30 July 2006
Available online 11 August 2006
Abstract
The complex [Ni(L1)2(py)2]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas
co-crystals having composition 2[Ni(L1)2(py)3(H2O)] Æ [Ni(L1)2(py)2(H2O)2] Æ 2py Æ 2H2O was obtained from solution state reaction.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Self-assembly; Co-crystals; Glycine derivatives; Metal complexes; C–Hꢀ ꢀ ꢀp interactions
Metal directed assembly of molecules is not only gov-
erned by coordination mode of metal ion but also directed
by various non-covalent forces originating from the struc-
tural features of ligand/s of choice [1]. These weak yet
reversible and directional interactions such as hydrogen-
bonding and p–p interactions are widely explored to design
superstructures with novel properties in the field of inor-
ganic crystal engineering [2]. However, unlike hydrogen-
bonding, the p–p interactions are less directional and hence
the structural features of any p-stacked system are less pre-
dictable [3]. Moreover the p-interactions are weak in solu-
tions to correlate relative orientations of p-stacked species
in solid state with high degree of certainty [4]. Among dif-
ferent metal-organic frameworks the metal carboxylate
frameworks have important status for their structural ver-
satility and scope for studying as porous material [5]. In
our recent study we have shown the importance of weak
interactions in inorganic and organic derivatives of N-
phthaloylglycine and in N-phthaloylglycylglycine [6–8]. It
would be interesting if these interactions can be guided so
that the each of them become competitive and surpass each
other to guide the structural features. From our recent
experiences and from existing literature on phthaloyl
related systems it is felt that the p–p and C–Hꢀ ꢀ ꢀp interac-
tions may guide structure of self-assembly [9]. In order to
study the mutual interplay of hydrogen bonding and p-
stacking interactions in metal directed assemblies we have
decided to use N-phthaloylglycine (L1), 4-carboxy-N-
phthaloylglycine (L2) and N-phthaloylglycylglycine (L3)
as ligands for complexation for comparative purpose of
which the structure of the ligands L3 [7] and L1 [10] have
been reported recently.
O
O
O
H
N
O
N
N
N
OH
OH
HO
OH
O
O
O
O
O
O
O
L3
L1
L2
The solid-state reaction of N-phthaloylglycine (L1) with
nickel(II)chloride hydrate in the presence of potassium
hydroxide followed by addition of pyridine gave the corre-
sponding carboxylate complex with two pyridine and two
aqua-ligands (Eq. (1)). The crystal structure of the complex
was determined and is shown in Fig. 1. The compound has
a self-assembled structure in which both intra- and inter-
molecular hydrogen-bonding plays a crucial role. The
important bond angles and hydrogen bond geometries
are listed in Table 1. The toluene molecules are held in
*
Corresponding author. Tel.: +91 361 2582301; fax: +91 361 2690762.
˚
the lattice through C–Hꢀ ꢀ ꢀp interactions (dCꢀ ꢀ ꢀp 3.74 A).
E-mail address: juba@iitg.ernet.in (J.B. Baruah).
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.07.038

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N. Barooah et al. / Inorganic Chemistry Communications 9 (2006) 1251–1254
The visible spectra of the complex have absorption at
637 nm typical of an octahedral geometry and occur due
it to be a co-crystal of two molecules of [Ni(L1)2-
(py)3(H2O)] with one molecule of [Ni(L1)2(py)2(H2O)2]
along with two molecules each of pyridine and water.
The structure is shown in Fig. 2. We have mentioned about
this complex in our earlier report [6], however, without
structural details. This complex is interesting for two rea-
sons. Firstly it is a co-crystal containing two independent
inorganic complexes having difference in the composition
but derived from same set of ligands. Secondly the self-
assembly formed has some uncoordinated ligand suggest-
ing it to be an intermediate meta-stable compound. The
compound in solid state at room temperature has a very
weak ESR signal at 3370 G and in pyridine solution it
has a relatively improved signal centering at 3410 G. Ther-
mogravimetry of the compound shows weight loss of 33%
at 83–318 °C which corresponds to loss of the pyridine and
water molecules. Metastable nature of the compound is
revealed from the ESI mass spectra of the compound, in
DMF solution it has the highest mass at 483.0; corresponds
3
3
to A2 ! T1 transition.
O
toluene
O
N
[Ni(L1)2(py)2(H2O)2].C7H8
+ KOH + py
+ NiCl2.6H2O
OH
1
O
L1
Ni(OAc)2.2H2O / ethanol
py/H2O
2[Ni(L1)2(py)3(H2O)] . [Ni(L1)2(py)2(H2O)2].2py.2H2O
2
ð1Þ
The co-crystals of inorganic complex with another inor-
ganic complex is not common; however, during our study
we have observed that when nickel(II)acetate was treated
with N-phthaloylglycine, a water insoluble complex was
obtained, which on dissolution in pyridine followed by
recrystallisation gave a compound (2) having much differ-
ent composition then the complex that was prepared by
solid-state reaction. X-ray diffraction study has revealed
Fig. 2. Crystal structure of co-crystals of 2[Ni(L1)2(py)3(H2O)] Æ [Ni(L1)2-
(py)2(H2O)2] Æ 2pyÆ2H2O (the hydrogen atoms are omitted for clarity; 50%
thermal ellipsoid).
Fig. 1. Hydrogen bonded self-assembly of bis-(pyridine)-bis(aqua)-bis-(N-
phthaloylglycinato) nickel(II).toluene (1) (30% thermal ellipsoid).
Table 1
Hydrogen-bonding interactions in 1
˚
˚
˚
˚
Hydrogen Bond
dDꢁH(A)
dAꢀ ꢀ ꢀH(A)
dDꢀ ꢀ ꢀA(A)
\D–H A (°)
ꢀ ꢀ ꢀ
O(9)–H(9A)ꢀ ꢀ ꢀO(2) [1 ꢁ x,2 ꢁ y,ꢁz]
O(9)–H(9B)ꢀ ꢀ ꢀO(6) (Intramolecular)
O(10)-H(10A)ꢀ ꢀ ꢀO(2) (Intramolecular)
O(10)–H(10B)ꢀ ꢀ ꢀO(4) [1 ꢁ x,2 ꢁ y,ꢁz]
C(15)–H(15)ꢀ ꢀ ꢀO(8) [ꢁx,2 ꢁ y,1 ꢁ z]
0.81
0.77
0.82
0.69
0.93
1.96
1.89
1.86
2.16
2.49
2.767(2)
2.653(3)
2.623(3)
2.822(3)
3.249(5)
174
172
154
162
139

N. Barooah et al. / Inorganic Chemistry Communications 9 (2006) 1251–1254
1253
to a Ni(L1)2(H2O) cation. The complex 1 and 2 has similar
IR spectra but the complex 2 has additional absorptions at
the crystal structure of the N-phthaloylglycine is known
to have dimeric structure from the H-bonding between
two carboxylic acid groups [10]. In the crystal lattice of
N-phthaloylglycine the dipoles of the aromatic part is
arranged on top of each other, so as to minimise the repul-
sion from the similar end of dipoles. The packing of the
nickel complex of L2 has similar features in the crystal
lattice, however, the rings interact with each other through
1485, 1476, 1447, 1191, 1217 cmꢁ1
.
The compound L2 has two carboxylic acid groups, of
which one carboxylic acid group is attached to the aro-
matic ring and other is attached to a methylene group.
These carboxylic acid groups of the ligand L2 differ in reac-
tivity [8]. For instance to form the nickel(II) and manga-
nese(II) complexes only one of the acidic hydrogen of
carboxylic acid of the ligand L2 gets deprotonated, leaving
aside another proton of carboxylic acid group intact. These
molecules thus serve as examples for metallo-organic
hybrid acids. Reaction of 4-Carboxy N-phthaloylglycine
(L2) with manganese(II)acetate and nickel(II)acetate is
shown in the Eq. (2).
˚
˚
C–Hꢀ ꢀ ꢀp [dCꢀ ꢀ ꢀp 3.71 A (complex 3); 3.74 A (complex 4)]
and aromatic p–p stacking interactions as depicted in
Fig. 3. The p–p separation between the aromatic rings in
˚
˚
compounds 3 and 4 is 3.37 A and 3.31 A, respectively. This
is well within the permissible limit for p–p stacking [9]. Due
to such interactions and the steric reasons the COOH
groups attached to the aromatic ring remains free and they
also do not self-assemble among themselves but are hydro-
gen bonded to the lattice water. The structures and the
hydrogen-bonding in the lattice resemble similar metallo-
hybrid acid of zinc that we had reported recently [8].
O
O
Mn(II)/ Ni(II)
OH
N
M(L2)2(4H2O).2H2O
HO
Water
O
O
M
= Mn(II) [3], Ni(II) [4]
L2
O
O
O
ð2Þ
The structure of these two complexes 3 and 4 are deter-
Cobalt(II)acetate
C
N
H
N
OH
Co(L3)2(4H2O)
ð3Þ
Water
O
mined by X-ray crystallography and found them to be iso-
structural. The structure of the nickel complex is given in
Fig. 3a. The nickel centers have octahedral environment
with two 4-Carboxy N-phthaloylglycinato ligands in
trans-disposition. The mono-anion of the ligand L2 is
formed through deprotonation of the carboxylic acid at
the glycine part. So far, we have not been able to crystallize
L2 in suitable form for crystallographic study. However,
5
L3
Further to this we have also prepared the cobalt(II)
complex of N-phthaloylglycylglycinato ligand (Eq. (3))
from the reaction of cobalt(II)acetate with N-phthaloylgly-
cylglycine in water. The crystal structure of this compound
is determined and found to have an octahedral geometry
Fig. 3. Intermolecular aromatic p–p stacking interactions between the N-phthaloyl groups in (a) complex 4 and (b) complex 3.

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N. Barooah et al. / Inorganic Chemistry Communications 9 (2006) 1251–1254
Fig. 4. The ORTEP diagram of (a) tetra-aqua bis-N-phthaloylglycylglycinato cobalt(II) (5) (b) the N–Hꢀ ꢀ ꢀO interaction leading to b sheet structure (N–
˚
Hꢀ ꢀ ꢀO 3.048 A and 160.37 °).
around the cobalt center (Fig. 4). In this compound the N-
phthaloylglycylglycinato ligands are positioned in trans-
disposition to each other, whereas the four water molecules
are in one plane. It is also interesting to note that the pres-
ence of phthaloyl group on the ligand adopts a b-pleated
sheet structure in the crystal lattice. This complex also
has the structural features that are recently reported for
zinc and cobalt complexes [7].
References
[1] K. Biradha, M. Fujita, in: G.R. Desiraju (Ed.), Perspective in
Supramolecular Chemistry: Crystal Design, Structure and Function,
vol. 7, Wiley, New York, 2003.
[2] (a) D. Braga, J. Chem. Soc. Dalton. Trans. (2000) 3705–3713;
(b) A.J. Blake, N.R. Champness, P. Hubberstey, W.-S. Li, M.A.
Withersby, M. Schroder, Coord. Chem. Rev. 183 (1999) 117–138;
(c) L.-L. Li, K.-J. Lin, C.-J. Ho, C.-P. Sun, H.-D. Yang, Chem.
Commun. (2006) 1286–1288;
Thus, we have demonstrated the supramolecular fea-
tures of functionalised glycine derivatives are a prominent
feature that is to be accounted in their metal complexes.
It is also observed that slight structural variation on glycine
can result into complexes having different implications such
as formation of meta-stable co-crystals, metallo-hybrid
acids, and systems having b-pleated structure, adding fur-
ther insight to the conventional co-ordination chemistry.
(d) L.W. Huang, C.J. Yang, K.J. Lin, Chem. Eur. J. 8 (2002) 396–400.
[3] C. Janiak, J. Chem. Soc. Dalton Trans. (2000) 3885–3896.
[4] J.A. Marsden, J.J. Miller, L.D. Shirtcliff, M.M. Haley, J. Am. Chem.
Soc. 127 (2005) 2464–2476.
[5] (a) C.N.R. Rao, R. Natarajan, R. Vaidyanathan, Angew. Chem. Int.
Ed. Eng. 43 (2004) 1466–1496;
(b) M.H. Zeng, X.L. Feng, X.M. Chen, J. Chem. Soc. Dalton Trans.
(2004) 2217–2223;
(c) S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D.
Williams, Science 283 (1999) 1148–1150;
(d) B. Chen, M. Eddaoudi, T.M. Reineke, J.W. Kampf, M. O’Keeffe,
O.M. Yaghi, J. Am. Chem. Soc. 122 (2000) 11559–11560;
(e) B. Chen, S.T. Eddaoudi, S.T. Hyde, M. O’Keeffe, O.M. Yaghi,
Science 291 (2001) 1021–1023.
Acknowledgements
The authors thank Department of Science and Technol-
ogy, New Delhi, India, for financial assistance. The authors
also thank Dr. A.S. Batsanov for solving the structure of
complex 2.
[6] N. Barooah, R.J. Sarma, A.S. Batsanov, J.B. Baruah, Polyhedron 25
(2006) 17–24.
[7] N. Barooah, R.J. Sarma, J.B. Baruah, Eur. J. Inorg. Chem. (2006)
2942–2946.
[8] K. Deka, N. Barooah, R.J. Sarma, J.B. Baruah, J. Mol. Struct., in
press doi:10.1016/j.molstruc.2006.05.005.
Appendix A. Supplementary materials
[9] (a) R.J. Sarma, C. Tamuly, N. Barooah, J.B. Baruah, J. Mol. Struct.,
in press doi:10.1016/j.molstruc.2006.06.006;
The synthetic procedures and crystallographic table for
the compounds reported is available as supplementary
materials. The CIF files of the compounds are deposited
to Cambridge Crystallographic database center and have
the CCDC numbers 603938, 612371, 612372, 613623 and
613624. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.inoche.2006.07.038.
(b) X.-Q. Lu, L. Zhang, C.-L. Chen, C.-Y. Su, B.-S. Kang, Inorg.
Chim. Acta. 358 (2005) 1771–1776;
(c) X.-Q. Lu, L. Zhang, C.-L. Chen, C.-Y. Su, B.-S. Kang, S.W. Ng,
Acta. Crystal. Sec. E. 59 (2003) 1891–1893;
(d) D.L. Reger, J.D. Elgin, R.F. Semeniuc, P.J. Pellechia, M.D.
Smith, Chem Commun. (2005) 4068–4069.
[10] N. Barooah, R.J. Sarma, A.S. Batsanov, J.B. Baruah, J. Mol. Struct.
721 (2006) 122–130.