Supramolecular Self-Assembly of M-IDA Complexes Involving Lone

ARTICLE pubs.acs.org/crystal

Supramolecular Self-Assembly of M-IDA Complexes Involving Lone-Pair 3 3 3 π Interactions: Crystal Structures, Hirshfeld Surface Analysis, and DFT Calculations [H2IDA = iminodiacetic acid, M = Cu(II), Ni(II)] Saikat Kumar Seth,$,‡ Indranil Saha,† Carolina Estarellas,§ Antonio Frontera,*,§ Tanusree Kar,*,$ and Subrata Mukhopadhyay*,† $

Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India Department of Physics, M. G. Mahavidyalaya, Bhupatinagar, Midnapore (East), West Bengal 721 425, India † Department of Chemistry, Jadavpur University, Kolkata 700 032, India § Department of Chemistry, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Baleares), Spain ‡

bS Supporting Information ABSTRACT: Mononuclear copper(II) and nickel(II) complexes, [(C5H6N2)Cu(IDA)(H2O)] (1) and (C5H7N2)2[Ni(IDA)2(H2O)] (2) [H2IDA = iminodiacetic acid; C5H6N2 = 4-aminopyridine; C5H7N2 = protonated 2-aminopyridine], have been synthesized, and their crystal structures were solved using single crystal X-ray diffraction data. A detailed analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions, which are crucial in building different supramolecular architectures. Molecules are linked by a combination of N
H 3 3 3 O, O
H 3 3 3 O and C
H 3 3 3 O hydrogen bonds into two-dimensional framework, whose formation is readily analyzed in terms of substructures of lower dimensionality with zero finite zero-dimensional dimeric units as the building blocks within the structures. Moreover, the aromatic molecules that are engaged in lone pair 3 3 3 π interactions with the noncoordinated carbonyl moieties play a crucial role in stabilizing the self-assembly process observed for both complexes. Intricate combinations of hydrogen bonding, lone pair 3 3 3 π and π
π interactions are fully described along with the computational studies.

’ INTRODUCTION 1
3

The construction of metal
organic frameworks (MOFs) through crystal engineering has attracted tremendous attention, partly because of their intriguing molecular topologies for aesthetic appeal4
6 and due to their various potential applications.7,8 MOFs are the result of spontaneous supramolecular self-assembly process of ligands and metal centers via metal
ligand coordination (MLC) and many other nonbonded interactions. However, the supramolecular structure of MOF is dependent on many parameters, such as the dynamic nature of metal ligand bonds, various coordination geometries of the metal centers, the nature and ligating topologies of the ligands used, the metal
ligand ratio, the nature of the counterions and the various experimental conditions such as solvents, temperature and crystallization methods. Combination of both MLC and hydrogen bonding in designing MOFs should be considered an attractive strategy because of the possibility of structural variations and guest entrapment induced r 2011 American Chemical Society

by specific hydrogen bonding interactions. Among the two branches of crystal engineering flourished simultaneously, one branch focused on the manipulation of coordination bond in designing the structure of MOF by judicial choice of metal and ligand. Whether, the other focused on the exploration of how weak interactions work individually or cooperativity in the supramolecular structure of an organic, organometallic solids and organic
inorganic hybrids.9,10 With the development of both the areas, a trend is emerging among the crystal engineers to make an interrelation between the two approaches: i.e. how weak interactions play an important role in designing the structure of a MOF. The self-assembly11 of molecular species via noncovalent interactions is one of the fundamental techniques that have been Received: April 20, 2011 Revised: May 18, 2011 Published: May 24, 2011 3250

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Crystal Growth & Design used to construct supramolecular architectures. Noncovalent interactions between the molecules are weak intermolecular contacts that play a pivotal role in biological systems and govern the physiochemical properties of molecular system in the condensed phase.12 Noncovalent binding interactions are now-adays commonly used for the self-assembly of large supramolecular aggregates in solution with specific chemical properties.13 Supramolecular interactions of aromatic systems have attracted considerable attention during the past decades,14 because of the utilization of intermolecular noncovalent interactions is relied upon for the design and development of novel functional materials. Various weak dispersive interactions, such as hydrogen bonding,15 π
π stacking,16 cation
π,17 C
H 3 3 3 π18 contacts represent the backbone of self-assembly process and supramolecular building blocks. In recent years, anion
π interactions19 has been recognized as supramolecular interaction by the scientific community, which was thought to be improbable because of the repulsive interactions among the aromatic clouds and electron rich molecules.20,21 Egli and co-workers have been extended this concept and reported an outstanding lone-pair 3 3 3 π interaction in a biomacromolecule, that is, Z-DNA.22 They also reported a remarkable example of H2O 3 3 3 π interactions within a ribosomal frame-shifting RNA pseudoknot.23 Egli and co-workers have pointed out the different possible orientations of a carbonyl group over the interacting π-face of aromatic rings.24 The carbonyl group (i) may be stacked onto the plane of the ring, (ii) may form an angle 0° < R < 90° with the ring plane, or (iii) may be perpendicular to the ring plane.24 Recently, lone pair
π bonding contacts have been evidenced in small molecular host
guest systems,25
27 and a number of computational studies have been demonstrated that such interactions between a lone pair donor and an aromatic acceptor can energetically favorable.28 Very recently, in a comprehensive review,27b Gamez et al. designated such lone pair 3 3 3 π contacts as a new supramolecular bond and rigorous analysis of the Cambridge Structural Database (CSD) revealed that such contacts are not unusual in organic or coordination compounds but have been overlooked in the past and this lone pair 3 3 3 π interactions are actually ubiquitous in solid state structures.29 Self-assembly via weak interaction has been manifested as a useful and powerful protocol for the construction of predesigned and well-defined aechitectures. Hirshfeld surface30,31 based tools represents a unique approach to the crystal structure prediction and this method offers a facile way of obtaining information on trends in crystal packing. The derivation of Hirshfeld surface and breakdown of the corresponding 2D fingerprint-plot30,32 provide a convenient means of quantifying the interactions within the crystal structures, revealing significant similarities and differences between related structures by individuate the packing motifs and offering considerable potential in crystal engineering. This plot provides information not only about close contacts, also about more distant contacts and areas where the interactions are weakest. Moreover, the fingerprint plots do not scale with molecular size- the size of the plot is constant irrespective of the number of atoms in the molecule, makes it appropriate for comparing crystal structure of molecules that are different in size. Analysis of intermolecular interactions using Hirshfeld surface base tools represent a major advance in the crystal structure prediction and should be considered by the supramolecular chemist to build multidimensional molecular structures. Therefore, the current research investigations are aimed at systematically studying this type of noncovalent bonding

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interactions observed in new crystal structures, to gain knowledge in this nascent field, both theoretically and experimentally. In this context, our serendipititous discovery of carbonyl(l.p.) 3 3 3 π/ π
π/carbonyl(l.p.) 3 3 3 π and lone pair 3 3 3 π/π 3 3 3 lone pair supramolecular associations in the solid state structure of metal
organic hybrid complexes sheds light on the potentiality of such newly discovered supramolecular forces in organizing and stabilizing molecular components in crystals. An investigation of close intermolecular contacts between the molecules via Hirshfeld surface analysis is also presented to reveal subtle differences and similarities of IDA molecules in the title crystal structures. The binding energies associated to the noncovalent interactions observed in the crystal structures and the interplay between them have been calculated using theoretical DFT calculations.

’ EXPERIMENTAL SECTION Materials and Measurements. All reactions were carried out in aerobic condition and in aqueous medium. Iminodiacetic acid (Aldrich), basic copper(II) carbonate (Sigma), nickel(II) acetate tetrahydrate (Aldrich), and aminopyridines (Aldrich) were used as received. Doubly distilled and then freshly boiled water was used throughout. Elemental analyses (C, H, N) of both complex were performed on a Perkin
Elmer 240C elemental analyzer. Preparation of Complex 1. Basic copper(II) carbonate, CuCO3 3 Cu(OH)2 (0.221 g, 1.0 mmol), was reacted with iminodiacetic acid (0.266 g, 2.0 mmol) in water (25 mL) nearly at 70 °C until a clear solution resulted. A warm aqueous solution (20 mL) of 4-aminopyridine (0.188 g, 2 mmol) was then added dropwise to the above solution with continuous stirring for about half an hour at normal laboratory temperature (∼30 °C). The solution mixture was then left undisturbed for a few days when plateshaped, light blue crystals suitable for X-ray diffraction analysis were obtained. The crystals were collected by filtration, washed with cold water and dried in air (yield = 50%). Anal. Calcd for C9H13N3O5Cu: C, 35.21; H, 4.24; N, 13.69%. Found: C, 35.10; H, 4.11; N, 13.59%. Preparation of Complex 2. Nickel(II) acetate tetrahydrate (0.248 g, 1.0 mmol) dissolved in 50 mL of water was allowed to react with iminodiacetic acid (0.266 g, 2.0 mmol) in water (25 mL) at 50 °C, resulting in a clear green solution. A warm aqueous solution (20 mL) of 2-aminopyridine (0.376 g, 4.0 mmol) was added dropwise to the above solution with continuous stirring. The reaction mixture thus obtained was further heated at 70 °C for three hours with continuous stirring. The solution was then cooled to room temperature and filtered, and the filtrate was left unperturbed. After a few weeks, block-shaped, pale green crystals, suitable for X-ray diffraction analysis were obtained. The crystals were collected by filtration, washed with cold water, and dried in air (yield = 40%). Anal. Calcd for C18H28N6O10Ni: C, 39.51; H, 5.16; N, 15.35%. Found: C, 39.47; H, 5.12; N, 15.38%. X-ray Crystallography Study. Single crystals of the title complexes were harvested directly from the slow evaporation method, and in all cases, suitable single crystals (i.e., those found by inspection to have welldefined morphology and that extinguished plane polarized light uniformly) were attached to the end of a MiTeGen mount using paratone oil. X-ray diffraction intensity data of the title complexes were collected at 150(2)K using a Bruker APEX
II CCD diffractometer. The system was operated at 1.2 Kw power (40 Kv, 30 mA) using graphite monochromated MoKR radiation (λ = 0.71073 Å). Data reduction was carried out using the program Bruker SAINT.33 An empirical absorption correction SADABS34 based on multiscan method was applied. The structure of the title compound was solved by direct methods and refined by the full-matrix least-squares technique on F2 with anisotropic thermal parameters to describe the thermal motions of all non hydrogen atoms using the programs SHELXS97 and SHELXL97.35 In the title 3251

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Table 1. Crystal Data and Structure Refinement Parameters for 1 and 2 1

2

empirical formula

C9H13N3O5Cu

C18H28N6O10Ni

formula weight temperature (K)

306.76 120(2)

547.17 120(2)

wavelength (Å)

0.71073

0.71073

crystal system

monoclinic

triclinic

space group

P21/c

P1

a, b, c (Å)

5.955(4), 9.929(9), 19.717(5)

5.063(2), 11.0850(10), 11.423(2)

R, β, γ (deg)

90.0, 95.841(5), 90.0

114.762(2), 94.467(2), 91.7430(10)

volume (Å3)

1159.8(13)

579.0(3)

Z/density (calcd) (Mg/m3) absorption coefficient (mm
1)

4/1.757 1.901

1/1.569 0.905

F(000)

628

286

crystal size (mm3)

0.21  0.14  0.06

0.28  0.19  0.09

θ range for data collection (deg)

2.08
25.0

1.97
25.0

reflections collected/unique

10524/2039 [R(int) = 0.0281]

3841/1996 [R(int) = 0.0672]

completeness to θ (%)

100.0

98.5

absorption correction

semiempirical from equivalents

semiempirical from equivalents

max. and min transmission refinement method

0.89 and 0.73 full-matrix least-squares on F2

0.92 and 0.81 full-matrix least-squares on F2

data/restraints/parameters

2039/9/176

1996/5/171

goodness-of-fit on F2

1.062

1.216

final R indices [I > 2σ(I)]a

R1 = 0.0376, wR2 = 0.0973

R1 = 0.0608, wR2 = 0.1587

R indices (all data)a

R1 = 0.0412, wR2 = 0.0995

R1 = 0.0836, wR2 = 0.1919

largest diff. peak and hole (e Å
3)

0.67 and
0.67

1.118 and
1.440

R1 = ∑||Fo|
|Fc||/∑|Fo|, wR2 = [∑{(Fo2
Fc2)2}/∑{w(Fo2)2}]1/2, w = 1/{σ2(Fo2) þ (aP)2 þ bP}, where a = 0.0440 and b = 1.6216 for 1 and a = 0.0728 and b = 0.6747 for 2. P = (Fo2 þ 2Fc2)/3 for both the structures. a

complexes, dfix and dang constraints were applied. All calculations were carried out using WinGX system Ver-1.64.36 The refinement was based on F2 for all reflections except those with nonreliable F2 values. All N
H and O
H hydrogen atoms were located from difference Fourier map and treated as riding where the isotropic thermal parameters of these hydrogen atoms were fixed as a multiple of the equivalent isotropic thermal parameters of the parent atoms. All other hydrogen atoms were placed at their geometrically idealized positions. A summary of crystal data and relevant refinement parameters are given in Table 1. CCDC 813062 (1) and 813063 (2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Hirshfeld Surface Analysis. Molecular Hirshfeld surfaces30,31 in the crystal structure are constructed basing on the electron distribution calculated as the sum of spherical atom electron densities.37 For a given crystal structure and set of spherical atomic electron densities, the Hirshfeld surface is unique,38 and it is this property that suggests the possibility of gaining additional insight into the intermolecular interaction of molecular crystals. The Hirshfeld surface enclosing a molecule is defined by points where the contribution to the electron density from the molecule of interest is equal to the contribution from all the other molecules. For each point on that isosurface two distances are defined: de, the distance from the point to the nearest nucleus external to the surface, and di the distance to the nearest nucleus internal to the surface. The normalized contact distance (dnorm) based on both de and di, and the vdW radii of the atom, given by the eq I enables identification of the regions of particular importance to intermolecular interactions.30 The value of the dnorm is negative or positive when intermolecular contacts are shorter or longer than vdW separations, respectively. Because of the symmetry between de and di in the expression for dnorm, where two Hirshfeld surfaces touch, both will display a red spot identical in color

intensity as well as size and shape. The combination of de and di in the form of a 2D fingerprint plot32 provides summary of intermolecular contacts in the crystal.30 The Hirshfeld surfaces are mapped with dnorm, and 2D fingerprint plots presented in this paper were generated using CrystalExplorer 2.1.39 In Crystal explorer, the internal consistency is important when comparing one structure with another, for the generation of Hirshfeld surfaces all bond lengths to hydrogen (or deuterium) atoms are set to typical neutron values (C
H = 1.083 Å, O
H = 0.983 Å, N
H = 1.009 Å).40 The 2D plots were created by binning (de, di) pairs in intervals of 0.01 Å and coloring each bin (essentially a pixel) of the resulting 2D histogram as a function of the fraction of surface points in that bin, ranging from blue (few points) through green to red (many points). Graphical plots of the molecular Hirshfeld surfaces mapped with dnorm using a red
white
blue color scheme, where red highlights shorter contacts, white is used for contacts around the vdW separation, and blue is for longer contacts. Moreover, two further colored properties based on the local curvature of the surface can be specified.41 Curvedness is a measure of “how much shape”; low values of curvedness are associated with essentially flat areas of the surface, while areas of sharp curvature possess a high curvedness and tend to divide the surface into patches associated with contacts between neighboring molecules. Shape index is a measure of “which shape”, and it can be sensitive to very subtle changes in surface shape, particularly in areas where the total curvature (or the curvedness) is very low. dnorm ¼

di
rivdW de
revdW þ revdW rivdW

ðIÞ

Theoretical Methods. The complexes studied in this work were computed at the RI-BP86/def2-TZVP level of theory by means of the program 3252

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Figure 1. ORTEP view and atom numbering scheme of the title complex 1 with displacement ellipsoid (Granite stone) at the 50% probability. TURBOMOLE version 5.7 using the crystallographic coordinates.42 We have used the BP86 method43 and the def2-TZVP44 basis set because this level of theory has been successfully used by some of us45 and others46 to theoretically study organometallic complexes. RI-DFT method applied to the study of weak interactions is considerably faster than the DFT and the interaction energies and equilibrium distances are almost identical for both methods.47 In addition the RI approximation is very efficient provided that the functional is of nonhybrid type.48 We have considered high spin density for the NiII atoms in the calculation of compound 2.

’ RESULTS AND DISCUSSION Crystal Structural Description of Compound 1. The molecular view49 of 1 is shown in Figure 1 with atom numbering scheme. Mononuclear complex 1 exhibit a roughly elongated square-base pyramidal coordination type 4 þ 1 for the Cu(II) atom, a mer-NO2 tridentate conformation for the IDA ligand, and the N-heterocyclic donor in the trans-site to the Cu
N(IDA) bond, both among four closest donor atoms of the metal surrounding. A search of the Cambridge Structural Database50 with Cu(II)IDA yielded 32 hits (excluding duplicate structure determinations), 22 of which had different coordination geometry, with the remaining 10 containing pyramidal geometry with different substituent groups except in AVEVIS,51 CUBNAO,52 HACBIX,53 ZORLIB54 where the second ligand coordinates the Cu(II) atom in the similar fashion. In 1, one N and two O donors from tridentate IDA ligand and the N donor from 4-aminopyridine define the distorted square basal coordination mean plane P(1). The Cu(II) atom is displaced 0.05(1)Å from this plane P(1) toward the apical O donor atom at 2.288(4)Å. The Cu
O5 bond is typically longer than other four coordination bonds. Because of Jahn
Teller effect, the axial Cu
O distances are somewhat longer than those of the other metal coordinated atoms, which completes the pyramidal coordination and forms the corresponding acute angles N(IDA)
Cu
O(carboxylate) are 84.2(2) and 83.7(2)° respectively (Supporting Information Table S1). The bond-length/angles agree well with the mean values of relevant bond distances obtained with MOGUL55 from searches based on related molecular fragments run on the CSD.50 As expected, the IDA is strictly planar and the Cu(II) atom lies 0.07(1) Å out from its aminopyridine plane P(2) which defines a dihedral angle (R) of 13.66(1)° with P(1).

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The percentage of trigonal distortion of the square pyramidal stereochemistry,56 obtained from the trans angles θ = N(1)
Cu(1)
N(2) and F = O(1)
Cu(1)
O(4), is τ = 100 (θ
F)/60 = 19.9. On the other hand, the dihedral angle between the mean planes for the two Cu-glycinate five-membered rings (j = 18.24°) shows the nearly coplanar conformation of the two chelating rings in the Cu(IDA) moiety. This structural feature agrees well with the nearly coplanar chelate rings in the Cu(IDA) moiety of the 1:1:1 Cu/IDA/N-heterocyclic donor compounds reported earlier.57 Such a finding is in contrast with the nearly perpendicular conformation of the chelate rings in the Cu(IDA) moiety of the diaqua complex [Cu(IDA)(H2O)2]58 as well as in those complexes having a 1:1:2 Cu/IDA/N-heterocyclic donor ratio.59 The solid state structure of complex 1 includes a combination of N
H 3 3 3 O, O
H 3 3 3 O, C
H 3 3 3 N, C
H 3 3 3 O, π
π, and carbonyl(l.p.) 3 3 3 π interactions. It is convenient to consider the substructures generated by each type of hydrogen bonds acting individually, and then the combination of substructures to build a three-dimensional framework. In 1, the amino N(3) atom in the molecule at (x, y, z) acts as a donor to the uncoordinated carboxylate oxygen atom O(2) in the molecule at (2
x, 1
y, 1
z). Consequently a centrosymmetric R22(20) dimeric ring (M) is generated, see Figure 2. Additional reinforcement between these molecules, which combine to form the M-type dimer, is provided by a pair of N3
H3C 3 3 3 O2(i) [(i) =
1 þ x, 1 þ y, z] hydrogen bonds with a characteristic R42(8) ring motif (N) (Figure 2). This two types of R22(20) and R42(8) rings in (1) are alternatively linked into infinite MNMN 3 3 3 chain propagating along (0 1 0) direction (Figure 2). The slight variation of the N
H 3 3 3 O bond distances may be attributed to the distinct crystal packing environments of the different complexes. The interconnection of the supramolecular dimeric rings (Mtype) of the molecules defining well-connected columns forms a supramolecular stacked ribbon in 1. The self-assembled structure of the title complex can be understood as a two-tier organization in which the hydrogen bonding between the fifth coordinated aqua ligand and non coordinated carboxylate unit has led to the formation of 2D layered assembly (Figure 3a). The two supramolecular dimeric layer (M-type) due to their inherent selfcomplementarities, form supramolecular tetramers through O5
H1O5 3 3 3 O3 hydrogen bonds which give rise to the R44(32) motif. This tetrameric unit can be considered as repeating units that generate the extended supramolecular layer structure (Figure 3a). The self-complementary nature of adjacent monomeric units and their affinity toward the aqua ligand are the crucial factors that govern the formation of 2D supramolecular layer in ab-plane where the molecules are aligned side by side along the a-direction. In another substructure, reinforcement between the molecules provided by a pair of N3
H3C 3 3 3 O2 hydrogen bonds and the pair of water oxygen O5 of aqua ligand acting as donor to carboxylate O3 at (1 þ x, y, z), forms another ring motif (Figure 3b) and can be represented using graph set notation60 as C11(10)C11(6)[R44(32)]. The organization of this tetrameric unit, producing a 2D supramolecular layer (Figure 3b), is achieved through the participation of strong self-complementary hydrogen bonding interactions. Here, the orientation of the monomeric units is such that it simultaneously facilitates self-complementary N
H 3 3 3 O hydrogen bonding with adjacent units, leads to optimal hydrogen-bonding (O
H 3 3 3 O) with the partner molecule and promotes unique recognition motifs in the bc-plane (Figure 3b). The interaction energy 3253

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Figure 2. Formation of 1D MNMN 3 3 3 chain through the self-complementary N
H 3 3 3 O hydrogen bonds giving rise to the formation of R22(20) and R42(8) hydrogen bonding motif propagating along (0 1 0) direction.

Figure 3. (a) Recognition of monomeric units through M type R22(20) hydrogen bonded dimeric motif leading to the formation of tetrameric R44(32) supramolecular layer. Hydrogen bonds not involve in hydrogen bonding have been omitted for clarity. (b) Formation of two-dimensional supramolecular layered assembly generated through R44(32) hydrogen bonding synthons.

Figure 4. Perspective view of the unique, sandwich-type carbonyl (l.p.) 3 3 3 π/π
π/carbonyl (l.p.) 3 3 3 π interaction leading to the formation of supramolecular assembly.

associated to the formation of the 2D layers via hydrogen bonds will be further studied and discussed in the theoretical part (vide infra).

The formation of a 3D supramolecular network is ensured by additional weak interactions. Primarily, the 2D sheets are interlinked by N
H 3 3 3 O and O
H 3 3 3 O hydrogen bonding interactions. These contacts are further supplemented by a face-toface π
π stacking interaction between the pyridine rings [R(1) = N(2), C(5)
C(9)] in the molecule at (x, y, z) and (1
x, 1
y, 1
z), respectively. Significant results are as follows: centroid
centroid distance d(CI
CJ) = 3.606(4) Å, R = 0°; d(perp CI
CJ) = 3.549(2) Å; β = 10.13°; d(perp CJ
CI) = 3.549(2) Å; γ = 10.13°; slippage = 0.635 Å. The intercentroid distances, the dihedral angle R between the first ring mean plane and the second ring mean plane of the partner molecule are in agreement with parallel displaced or offset face-to-face π stacking interactions (Figure 4). An unusual contact between CdO group of IDA ligand and the π-system of aminopyridine is observed (Figure 4), where the noncoordinating O3 atom is oriented toward the π-face and is responsible for the formation and strengthening of the 3D assembly. The separation distance between the uncoordinated carboxylate oxygen O3 (which is also involved in three strong H-bonds; see Table 2) and the centroid of the 4-aminopyridine ring is 3.810(5) Å [C4 3 3 3 Cg(1) = 4.042(5) Å, where Cg(1) is the centroid of the ring defined by atoms N2, C5
C9; Symmetry 3254

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Table 2. Hydrogen Bonding Geometry of C9H13N3O5Cu (1) (Å, deg) D
H 3 3 3 A

d(D
H)

d(H 3 3 3 A)

N3
H3C 3 3 3 O2 N3
H3D 3 3 3 O2

0.86

2.26

2.952(5)

138


1 þ x, 1 þ y, z

0.86

2.01

2.866(5)

174

2
x, 1
y, 1
z

N1
H11 3 3 3 O3 O5
H1O5 3 3 3 O3

0.67

2.49

3.095(7)

151

1 þ x, y, z

0.89

2.14

2.931(5)

148

1 þ x, y, z

O5
H2O5 3 3 3 O3 C2
H2B 3 3 3 N3

0.77

2.07

2.718(6)

142

1
x, 1/2 þ y, 1/2
z

0.97

2.62

3.579(6)

169

x,
1 þ y, z

code: 1
x,
1/2 þ y, 1/2
z]. In this case, the carbonyl oxygen O3 approaches the π-face with an angle of 91.8(2)°, suggesting a significant lone pair 3 3 3 π interaction.24 The shortest separation distances reflecting this interaction are O3 3 3 3 N2 = 3.573(2)Å and O3 3 3 3 C9 = 3.623(2)Å and are therefore below the sum of the corresponding van der Walls radii. The occurrence of these CdO(l.p.) 3 3 3 pyridine contacts produces a unique sandwich-type carbonyl(l.p.) 3 3 3 π/π
π/carbonyl(l.p.) 3 3 3 π topology and increase the dimensionality of 1. An analysis of the CSD for lone pair 3 3 3 π interactions by Egli et al.24 showed that a significant carbonyl 3 3 3 π(aromatic) stacking interaction is suggested by an angle ω ranging from 25 to 64°, where ω being the dihedral angle between CdO bond and the plane of the aromatic ring. In 1, the orientation of the carbonyl group takes an angular approach toward the ring plane (ω ≈ 35.68°) and this orientation potentially allows hydrogen bonding interactions with the O lone pairs. Moreover, the distance D (distance between the carbonyl oxygen atom and the ring centroid) and the angular distribution (deviation of R from 120°, where R is the angle between CdO 3 3 3 Cg) are 3.81 Å and 28.2°, respectively. These values are within the mean values, calculated by Egli et al.24 on the basis of favorable stacking CdO(l.p.)•••π interactions found in the CSD. We thus provide an example, where carbonyl
π interaction controls the self-organization of the Cu(II) complex even when the π-system of the aromatic ring is not electron poor. A likely explanation is that the Cu(II) bonded with pyridine nitrogen, withdraws electron density to some extent by polarizing the π-electron density of the ring,9 enhancing the (l.p.) 3 3 3 π interaction with the π-face of the aromatic ring and therefore facilitating the 3D supramolecular network. Crystal Structure Description of Compound 2. The molecular structure view49 of 2 is shown in Figure 5. The Ni(II) ion located on an inversion center is equatorially coordinated to one nitrogen atom (N1) and two oxygen atoms (O1, O4) from one IDA ligand (tridentate) and their symmetry related counterparts (N1*, O1*, O4*) (* =
x þ 1,
y,
z þ 1) from second IDA unit with a distorted octahedral geometry {Ni N2 O4}. A search of the Cambridge Structural Database50 with Ni(II)IDA yielded 7 hits, excluding duplicate structure determinations. From them, 3 hits (CILCAB,61 CSNIDA,62 and IMACNI63) exhibit the same coordination geometry as 2. In complex 2, the two IDA ligands are linked through the Ni atom in a typical fac-chelating arrangement with two nitrogen atoms in the trans positions. The Ni
N bond length is 2.075(4) Å, while Ni
O1 and Ni
O4 distances are 2.030(3) and 2.066(4) Å, respectively (Supporting Information Table S2). As expected, the bond lengths are agree well with the mean values of relevant bond distances obtained with MOGUL55 from searches based on related molecular frameworks run on the CSD.50 In either chelating

d(D 3 3 3 A)

D
H 3 3 3 A

symmetry

Figure 5. ORTEP view and atom numbering scheme of the title complex 2 with displacement ellipsoid (granite stone) at the 50% probability.

ring Ni1
O1
C1
C2
N1 and Ni1
O4
C4
C3
N1, all the atoms are coplanar with C2, N1 and C3, N1 atoms have largest deviations in opposite directions [C(2) = þ0.149(5) Å, N(1) =
0.134(4) Å; C(3) = þ0.191(5) Å, N(1) =
0.1556 Å] from the least-squares mean planes of the rings. The dihedral angle between the two chelating rings is 83.65(1)°. The molecular packing in 2 exhibits strong intermolecular N
H 3 3 3 O, O
H 3 3 3 O hydrogen bonds and weak C
H 3 3 3 O, CdO(l.p.) 3 3 3 π interactions. The N
H 3 3 3 O and O
H 3 3 3 O hydrogen bonds facilitate self-assembly of IDA molecules, forming different types of supramolecular architectures in 2; additional reinforcement within molecular framework is provided by C
H 3 3 3 O and CdO(l.p.) 3 3 3 π interactions. In (2), adjacent monomeric anionic [Ni(IDA)2]2
units are connected to one another via aminopyridine cations by strong complementary N
H 3 3 3 O hydrogen bonds. The amino N3 atom in the molecule at (x, y, z) acts as a donor to the O4 atom of the molecule at (1 þ x, y, z), which also donates a proton to the carbonyl O2 atom in the molecule at (x, y, z), so generating a centrosymmetric R44(16) dimeric ring and can be represented using the graph set notation60 as d11(2)d11(2)d11(2)d11(2) R44(16) (Figure 6a). This self-assembly propagates along (1 0 0) direction, generating an infinite 1D chain. Each monomeric anionic units also recognizes two aminopyridinium cations (C5H7N2þ) through doubly coordinated carboxylate ends, leading to d11(2) d11(2) R22(8) hydrogen bonding assemblies involving the N2
H2 3 3 3 O3 and N3
H3a 3 3 3 O4 hydrogen bonds (Table 3) in the molecule at (1 þ x, y, z) (Figure 6a). The self-assembled superstructure of the complex can best be 3255

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Figure 6. (a) Formation of 1D chain along (1 0 0) direction in 2 leading to the formation of R44(16) hydrogen bonding motif through the association of discrete [Ni(IDA)2]2
units. Each monomeric unit also recognizes aminopyridinium moiety to generate R22(8) cyclic motif. (b) Two-dimensional assembly with fused R22(8) and R88(26) rings in 2. 2-aminopyridine and hydrogen atoms not involve in hydrogen bonding have been omitted. (c) Formation of two-dimensional supramolecular sheet in (0 1 1) plane generated through dimeric rings in 2. Solvent water and hydrogen atoms not involve in hydrogen bonding have been omitted.

Table 3. Hydrogen Bonding Geometry of C18H28N6O10Ni (2) (Å, deg) D
H 3 3 3 A N1
H1 3 3 3 O1 N2
H2 3 3 3 O3 N3
H3A 3 3 3 O4 N3
H3B 3 3 3 O2 OW
H1W 3 3 3 O2 O1W
H2W 3 3 3 O1W O1W
H2WA 3 3 3 O1W C5
H5 3 3 C7
H7 3 3

3 O3 3 O2

d(D
H)

d(H 3 3 3 A)

d(D 3 3 3 A)

D
H 3 3 3 A

symmetry

0.91

2.04

2.930(5)

167

2
x,
y, 1
z

0.86

1.85

2.705(6)

173

1 þ x, y, z

0.86 0.86

2.09 2.25

2.870(6) 3.057(5)

150 156

1 þ x, y, z

0.88

2.06

2.878(5)

154

0.89

1.92

2.780(7)

162

1
x,
y,
z

0.90

1.90

2.776(7)

167

2
x,
y,
z

0.93

2.38

3.299(6)

168

2
x, 1
y, 2
z

0.93

2.44

3.306(7)

156

1
x, 1
y, 1
z

understood as a three tier organization in which the hydrogen bonding between the [Ni(IDA)2]2
units, the solvent water molecules and the aminopyridinium cations (C5H7N2þ) has led to the formation of 2D supramolecular architectures (Figure 6b,

6c) onto which aminopyrinine are attached through carbonyl(l.p.) 3 3 3 π interactions (Figure 7). The orientation of anionic units is such that it simultaneously facilitates (i) self-complementary strong N
H 3 3 3 O hydrogen bonding with adjacent [Ni(IDA)2]2
3256

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Figure 7. Supramolecular self-assembly generated through carbonyl 3 3 3 π/π 3 3 3 carbonyl interactions in 2.

units, (ii) leads to optimal hydrogen bonding with solvent water molecules, (iii) leads to hydrogen bonding with aminpyridinium units, and (iv) promotes unique recognition (CdO 3 3 3 π) motifs with aminopyridine molecules. Because of centrosymmetric coordination environment, the self-complementary nature of adjacent [Ni(IDA)2]2
units and their affinity toward solvent water molecules are the crucial factors that govern the formation of the 2D supramolecular sheet in the ac-plane. The chelating ring nitrogen N1 in the molecule at (x, y, z) acts as donor carboxylate oxygen O1 in the molecule at (2
x,
y, 1
z), so generating a centrosymmetric R22(8) dimeric ring centered at (1, 0, 1/2) and can be represented using the graph set notation60 as C11(4)C11(4)R22(8)(Figure 6b) and this self-complementary hydrogen bonding between the adjacent monomeric anionic [Ni(IDA)2]2
units gives rise to the formation of 1D parallel chain along (1 0 0) direction. The spreading of parallel chains separated by 11.42 Å in 2 is such that the IDA sites in the neighboring chains are orientated toward each other in the same way as the carboxylate carbonyl groups (Figure 6b). The overall 2D supramolecular built-up of the complex is the result of the self-assembly of a primary supramolecular dimeric unit (Figure 6b) through multi self-recognition. This multi way selfrecognition has been facilitate by the active participation of a solvent water molecule. The solvent water oxygen O1W acts as donor to the carbonyl oxygen O2 and acts as donor as well as acceptor to the neighboring water molecule at (1
x,
y,
z), so forming a tetrameric R88(26) ring. This two types of R22(8)

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and R88(26) rings in 2 are alternatively linked to complete the supramolecular framework in (1 0 1) plane (Figure 6b). The amine nitrogen N2 and ring carbon C5 of aminopyridinium cations in the molecule at (x, y, z) acts as donor to the carbonyl oxygen O3 in the molecule at (1 þ x, y, z) and (2
x, 1
y, 2
z), respectively, generates a R42(10) (M) ring motif (Figure 6c). Additional reinforcement between these molecules at (x, y, z) and (1
x, 1
y, 1
z) provided by a pair of C7
H7 3 3 3 O2 and with a pair of C5
H5 3 3 3 O3 hydrogen bonds with a characteristic R44(24) (N) ring. The two types of R42(10) and R44(24) rings in (2) are alternatively linked into infinite MNMN 3 3 3 chain propagating along [0 1 0] direction (Figure 6c). The neighboring parallel MNMN 3 3 3 chains are separated by 10.45 Å and the ring junctions of the parallel chains producing R44(26) (P) dimeric ring motifs and the combination of the rings suffices to generate a continuous two-dimensional framework structure (Figure 6c). The aminopyridinium molecules are also attached through the ring carbon C5 and the N3 of amine terminals to the uncoordinated carboxylate carbonyl oxygen O3 and O2 in the molecule at (2
x, 1
y, 2
z) and (x, y, z), respectively, to form R44(26) dimeric units (Figure 6). The noncoordinated carbonyl oxygen atoms (O2 and O3) both are oriented toward the π-face of 2-aminopyridinium moiety. The distance between O2 and the centroid of the aminopyridine ring is 3.628(4) Å [C1 3 3 3 Cg(5) = 4.873(6) Å where Cg(5) is the centroid of the aminopyridinium ring defined by atoms N2/C5
C9]. This carbonyl oxygen atom O2 approaches the π-face with an angle 178.2(3)° in the molecule at (2
x, 1
y, 1
z), therefore reflecting a significant lone pair 3 3 3 π interaction.24
27 The 2-aminopyridine ring is further stacked over another carbonyl oxygen O3, suggesting lone pair 3 3 3 π interaction and is responsible as well for the strengthening of the 3D assembly (Figure 7). The noncoordinating O3 atom is oriented toward the π-face with a distance of 3.295(5)Å to the centroid of the ring [C4 3 3 3 Cg(5) = 3.880(6)Å; C4
O3 3 3 3 Cg(5) = 108.4(3)°]. The occurrence of these CdO (l.p.)/pyridine contacts produces carbonyl (l.p.) 3 3 3 π/π 3 3 3 carbonyl(l.p.) topology (Figure 7). An analysis of the CSD for lone pair 3 3 3 π interaction by Egli et al.24 showed that a significant carbonyl(l.p.) 3 3 3 π(aromatic) stacking interaction is suggested by an angle ω ranging from 0 to 24° and 65
90°, ω being the dihedral angle between CdO bond and the plane of the aromatic ring. In 2, the orientation of the carbonyl groups (O2 and O3) are designated by ω = 87.17° and 19.60° respectively and represents that CdO(2) group heads directly into the ring plane whereas CdO(3) group is stacked on the ring plane. Moreover the distance D (corresponding to the distance between the carbonyl oxygen atom and the ring centroid) and the angular distribution (deviation of the angle R from 120°, where R is the angle CdO 3 3 3 Cg) are 3.30 Å and 11.6°, respectively, and these values are within the mean values, that is, 3.58 Å and 30.6°, calculated by Egli et al.24 on the basis of favorable stacking of CdO(l.p.) 3 3 3 π interactions found in the CSD. This entire assembly as a whole produces a rare supramolecular lone pair 3 3 3 π/π 3 3 3 lone pair network and illustrates the occurrence of an elegant combination of weak forces in the solidstate structure of a metal
organic hybrid complex (2). Hirshfeld Surface. The Hirshfeld surfaces of title complexes are illustrated in Figure 8, showing surfaces that have been mapped over dnorm (
0.5 to 1.5 Å), shape index and curvedness. The surfaces are shown as transparent to allow visualization of the molecular moiety, in a similar orientation for both structures, 3257

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Figure 8. Hirshfeld surface mapped with dnorm (left), shape index (middle), and curvedness (right) for the title complexes.

Figure 9. Fingerprint plots of 1 and 2: Full (left) and resolved into O 3 3 3 H/H 3 3 3 O (middle) and N 3 3 3 H/H 3 3 3 N (right) contacts showing the percentages of contacts contributed to the total Hirshfeld Surface area of molecules.

around which they were calculated. It is clear that the information present in Tables 2 and 3 is summarized effectively in these spots, with the large circular depressions (deep red) visible on the front and back views of the surfaces indicative of hydrogen-bonding contacts. Other visible spots in the surfaces are because of H 3 3 3 H contacts. The dominant interactions between N
H, O
H and carbonyl O atoms in both the compounds can be seen in the Hirshfeld surface as the red areas marked as a, b, c etc. in Figure 8. The small extent of area and light color on the surface indicates weaker and longer contact other than hydrogen bonds. The O 3 3 3 H/H 3 3 3 O intermolecular interactions appear as distinct spikes in the 2D fingerprint plot (Figure 9). Complementary regions are visible in the fingerprint plots where one molecule act as donor (de > di) and the other as an acceptor (de < di). The fingerprint plots can be decomposed to highlight

particular atoms pair close contacts.37a This decomposition enables separation of contributions from different interaction types, which overlap in the full fingerprint. The N
H 3 3 3 O intermolecular interactions appear as two distinct spikes in the 2D fingerprint plots, labeled correspondingly as a and b. The proportion of O 3 3 3 H/H 3 3 3 O interactions comprising 36.1% of the Hirshfeld surfaces for each molecule of 1, whereas that in 2 is 47.9%. The O 3 3 3 H interactions are represented by a spike (di = 0.751, de = 1.097 Å in 1 and di = 0.676, de = 1.026 Å in 2) in the bottom left (donor) area of the fingerprint plot (Figure 9), indicating that amino H-atoms interacting with O-atoms of the carbonyl groups and are responsible for the formation of dimeric rings. The H 3 3 3 O interactions are represented by a spike (de = 0.751, di = 1.097 Å in 1 and de = 0.676, di = 1.026 Å in 2) in the bottom right (acceptor) region of Fingerprint plot, where 3258

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Figure 10. Relative contributions of various intermolecular contacts to the Hirshfeld surface area in complex 1, complex 2, and some related structures retrieved from the CSD.

carbonyl oxygen also act as acceptor to the H atoms of the NH groups and these oxygen-based interactions represent the closest contacts in the structures and can be viewed as a pair of large red spots on the dnorm surface (Figure 8). The proportion of N 3 3 3 H interactions comprising 3.5% and 2.3% of the Hirshfeld surfaces for each molecule in 1 and 2, respectively. No significant C
H 3 3 3 π interactions are observed in both the compounds, with C 3 3 3 H close contacts varying from 6.5% in 1 to 8.4% in 2. A significant difference between the molecular interactions in the title complexes in terms of H 3 3 3 H interactions is reflected in the distribution of scattered points in the fingerprint plots, which spread only up to di = de = 2.2 Å in 1 and di = de = 2.4 Å in 2. The inspection of contacts between other atom types pointed out that there are also specific features in the C 3 3 3 O/O 3 3 3 C fingerprint plot (Figure 9) for both complexes. The clear green/ blue lines with the shortest (de þ di) ≈ 3.2 Å in 1 and (de þ di) ≈ 3.4 Å in 2 correspond to carbonyl (lone pair) interactions. It is worth noting that in the crystal of 2 those contacts are much more dispersed, significantly longer and cover only 1.4% of the Hirshfeld surface compairing to 3.2% in 1. The relative contribution of the different interactions to the Hirshfeld surface was calculated for the title complexes as well as similar metal
IDA complexes (Figure 10) available in the CSD. Because of varying the number and the types of substituents, they are not directly comparable across the title complexes, but it offers some insight into the effect of different substituent on the IDA backbone. With different substituents, the contribution of H 3 3 3 H interactions to the Hirshfeld Surface increases steadily up to well over 40% in 1 with a corresponding decrease in the contribution to 19.9% in HACBIX.53 The contribution of O 3 3 3 H interactions varies from 33.5% in CUBNAO52 to 52% in HACBIX53 and can be attributed to various substitutions on the molecular moiety, which in turn facilitates the formation of different supramolecular synthons, leading to diverse crystal packing arrangements. From the Hirshfeld surface of 1, it is clear that the crystal structures of the aminopyridinium moiety are related to one another, where above the plane of the molecule, inspection of the adjacent red and blue triangles on the shape index surface (Figure 8) shows that the π
π stacking interaction is almost identical in these crystal structures whereas there is no such existence in 2. In 1, π
π interactions are evident on the Hirshfeld surface as a large flat region across the molecule, which is most clearly visible on the curvedness surfaces. The pattern of red and blue triangles on the same region of the shape index

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surface is another characteristic of π
π interactions (Figure 8). Blue triangles represent convex regions because of the ring carbon atoms of the molecule inside the surface, while red triangles represent concave regions resulting from the carbon atoms of the π-stacked molecule above it. The pattern of alternating red and blue triangles with suitable symmetry is indicative of offset π
π stacking interactions characteristic of layers and this type of stacking is evident only in complex-1. Finally, these examples underline the utility of Hirshfeld surfaces and in particular, fingerprint-plot analysis for the “visual screening” and rapid detection of unusual crystal structures features64 through a “whole structure” view of intermolecular interactions.38 Theoretical Study. We have performed a computational study using DFT calculations to analyze the noncovalent interactions involved in the interesting 3D architectures of compounds 1 and 2. In particular, we have focused our efforts in two main issues. First, we have studied the energetic features of the noncovalent interactions that govern the crystal packing and, second, we have analyzed the interplay between them. In compound 1, we have studied two important aspects that control the crystal packing. The first one is the formation of the hydrogen bonding supramolecular dimers and tetramers shown in Figure 3. The formation of the dimer is governed by a double N
H 3 3 3 OdC hydrogen bond and the formation of the tetramer involves a π
π stacking interaction and two additional hydrogen bonds with the participation of the coordinated water molecule. We have computed the binding energies associated to each type of noncovalent interaction. Using the equation represented in Figure 11, we have estimated each N
H 3 3 3 OdC hydrogen bond, which is
9.72 kcal/mol at the RI-BP86/def2TZVP level of theory. The interaction energy of the stacking interaction shown at the bottom of Figure 11 is
2.18 kcal/mol. In addition, we have computed the formation energies of the supramolecular tetramer computed from several fragments of complex 1, as it is shown in Figure 12. The interaction energy associated to the OW
H 3 3 3 OdC hydrogen bonds can be estimated using the formation energy of the tetramer from two dimers (ΔE =
20.61 kcal/mol) and subtracting to this value the stacking interaction measure before (
2.18 kcal/mol, see Figure 11). Therefore each OW
H 3 3 3 OdC hydrogen bond contributes to the stabilization of the system in
9.22 kcal/mol, which is comparable to the N
H 3 3 3 OdC hydrogen bond. The second aspect that has been studied in complex 1 is the supramolecular CdO(l.p.) 3 3 3 π/π
π/CdO(l.p.) 3 3 3 π interaction, in particular the influence of the (l.p.) 3 3 3 π interaction on the stacking interaction. Some of us have previously demonstrated favorable cooperativity effects between anion 3 3 3 π and π
π stacking interactions.47,65 Therefore similar effects can be present in the CdO(l.p.) 3 3 3 π/π
π/CdO(l.p.) 3 3 3 π assembly observed in 1 (see Figure 4). To explore this issue we have computed the binding energy of the stacking interaction considering that the CdO(l.p.) 3 3 3 π interaction has been previously formed (see Figure 13). It can be observed that the double CdO(l.p.) 3 3 3 π interaction has a favorable influence on the π
π stacking interaction, which is reinforced from
2.18 kcal/ mol (absence of (l.p.) 3 3 3 π interaction, see Figure 11) to
4.95 kcal/mol in the presence of the two (l.p.) 3 3 3 π interactions. In Figure 13 we have also evaluated the (l.p.) 3 3 3 π interaction, which is very modest since the interaction energy of the stacked dimer with two additional molecules of complex 1 is only
0.69 kcal/mol, indicating that each (l.p.) 3 3 3 π interaction is almost negligible (
0.35 kcal/mol). A very interesting finding is 3259

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Figure 11. Interaction energies of the hydrogen bonded dimer (top) and the π
π stacked dimer of 1 (bottom).

Figure 12. Several combinations to yield the supramolecular tetramer of 1 are shown.

obtained when studying the mutual influence of both (l.p.) 3 3 3 interactions. When a single (l.p.) 3 3 3 π interaction is calculated using the equation used at the bottom of Figure 13, the interaction energy is
0.66 kcal/mol, almost twice the value obtained in the absence of the other (l.p.) 3 3 3 π interaction. This result

indicates that one (l.p.) 3 3 3 π interaction enhances the other and that the effect is transmitted through the π
π stacking interaction. This result also explains the formation of the supramolecular CdO(l.p.) 3 3 3 π/π
π/CdO(l.p.) 3 3 3 π assemblies, which have been previously observed in related systems.25 3260

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Figure 13. Equations used to evaluate the π
π stacking interaction in the presence of the (l.p.) 3 3 3 π interaction and vice versa in compound 1.

Figure 14. Formation energy of a fragment of complex 2 that establishes four anion
π interactions and two hydrogen bonds. Distances in Å.

The theoretical study on compound 2 is devoted to analysis of the CdO 3 3 3 π interactions. First of all, it should be commented that the dianionic nature of the [Ni(IDA)2]2
moiety entails that the interaction can be described as an anion
π interaction, which is very favorable because of the cationic nature of the aromatic ring (protonated 2-aminopyridine). Curiously, each [Ni(IDA)2]2


moiety interacts simultaneously with four 2-aminopyridine rings, establishing four anion
π interactions (see Figure 14). In addition, two protonated 2-aminopyridine rings also interact with the anion by means of hydrogen bonding interactions. The computed energy of formation is very large because the electrostatic ion-pair nature of these interactions. 3261

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Figure 15. Neutral fragment used to evaluate both types of anion
π interactions (A and B).

In an effort to evaluate the contribution of the two different anion
π interactions in this system we have used a fragment of the crystal structure that is neutral in order to minimize pure electrostatic effects. The fragment used is shown in Figure 15 and the two types of anion
π interactions (A and B) are indicated. Interaction A is more directional than B since the CdO bond

points to the center of the ring and the interaction energy is
28.7 kcal/mol. Interaction B is less directional and the CdO group is almost parallel to the aromatic ring plane. The equation shown at the middle of Figure 15 measures both the anion
π and the hydrogen bonding interaction. We have roughly evaluated the energy associated to the anion
π interaction computing a 3262

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Crystal Growth & Design model where the 2-aminopyridine has been oriented differently and, consequently, the hydrogen bond cannot be formed (see Figure 15, bottom). To achieve this we have changed the orientation of the amino group, which is pointing to the opposite direction. Therefore the estimated interaction energy for the type “B” anion
π is
34.76 kcal/mol, in agreement with the anion
π distances, which are 3.629 for “A” and 3.295 for “B”.

’ CONCLUSIONS We have demonstrated various supramolecular structural diversities as a function of the ligating topologies of the IDA ligand. The MOFs in the title complexes demonstrate the primary structural motifs that constitute the backbone of the net supramolecular arrangement are dictated by hydrogen bonds and other noncovalent contacts (lone pair 3 3 3 π and π
π) are found to govern the final solid-state packing of the molecules. Therefore the entire assembly as a whole produces a rare combination of lone pair 3 3 3 π/π
π/π 3 3 3 lone pair and lone pair 3 3 3 π/ π 3 3 3 lone pair network and illustrates the occurrence of an elegant combination of weak forces in the solid state structure of metal
organic hybrid complexes, which contributes to the self-assembly process. Hirshfeld surface is used to visualize the fidelity of computed crystal structures. The study of the title complexes underlines the way in which Hirshfeld surface and fingerprint plot analysis provides rapid quantitative insight into the intermolecular interactions in complex molecular solids. The Hirshfeld surfaces and fingerprint plots prove to be particularly suited for comparing the molecular environments in the title structures, which often exhibit complex interplay between the crystallographically independent molecules. The close contacts are dominated by O 3 3 3 H and H 3 3 3 H contacts and these relatively weak interactions have clear signatures in the fingerprint plots. Finally, the theoretical part provides an energetic study of the noncovalent interactions that are responsible of the supramolecular assemblies observed in the solid state. In addition, it demonstrates the existence of interesting cooperativity effects between the noncovalent interactions that is useful to understand the formation of the lone pair 3 3 3 π/π
π/π 3 3 3 lone pair assembly. ’ ASSOCIATED CONTENT

bS Supporting Information. Two crystallographic files (CIF) and Tables S1
S2 listing crystallographic data and selected bond lengths and angles for both complexes. This material is available free of charge via the Internet at http://pubs.acs.org. ’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (T.K.); [email protected] (A.F.); [email protected] (S.M.).

’ ACKNOWLEDGMENT S.K.S. is grateful to the DST-funded National Single Crystal X-ray Diffraction facility at the Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, India, for data collection. We thank CONSOLIDER-Ingenio 2010 (CSD201000065) and the MICINN of Spain (project CTQ2008-00841/ BQU, FEDER funds) for financial support. We thank the CESCA for computational facilities. C.E. thanks the MEC of Spain for a

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predoctoral fellowship. S.M. is grateful to UGC-CAS programme in the Department of Chemistry, Jadavpur University for financial support of this work. We thank Dr. M Barcelo-Oliver of Departament de Qu
imica, Universitat de les Illes Balears for helpful discussions.

’ REFERENCES


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