Malonate Complexes - American Chemical Society

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3‑Picoline Mediated Self-Assembly of M(II)−Malonate Complexes (M = Ni/Co/Mn/Mg/Zn/Cu) Assisted by Various Weak Forces Involving Lone Pair−π, π−π, and Anion···π−Hole Interactions Monojit Mitra,† Prankrishna Manna,† Antonio Bauzá,‡ Pablo Ballester,§,# Saikat Kumar Seth,∥ Somnath Ray Choudhury,*,⊥ Antonio Frontera,*,‡ and Subrata Mukhopadhyay*,† †

Department of Chemistry, Jadavpur University, Kolkata 700 032, India Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma (Baleares), Spain § Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona, Spain # Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys, 23, 08018, Barcelona, Spain ∥ Department of Physics, M. G. Mahavidyalaya, Bhupatinagar, Purba Medinipur, West Bengal, 721 425, India ⊥ Central Chemical Laboratory, Geological Survey of India, 15 A & B Kyd Street, Kolkata 700 016, West Bengal, India ‡

S Supporting Information *

ABSTRACT: Five M(II)−malonate complexes having a common formula (C 6 H 9 N 2 ) 4 [M II (C 3 H 2 O 4 ) 2 (H 2 O) 2 ](PF6)2.(H2O)2 (1−5) [where C6H9N2 = protonated 3picoline, M(II) = Ni/Co/Mn/Mg/Zn, C3H4O4 = malonic acid, and PF6− = hexafluorophospahte], have been synthesized and their crystal structures have been determined. Complexes 1−5 were found to be isostructural and protonated 3-picoline has primarily mediated the self-assembly process. Role of a discrete water dimer in complexes 1−5 was also studied. Weaker π−interactions have also played crucial role in stabilizing 1D chain constructed by discrete [MII(C3H2O4)2(H2O)2] units. An additional copper complex namely, (C6H9N2)4[Cu(C3H2O4)2](PF6)2 (6) has been synthesized from the same reagents and was found to have a completely different structure from the others. Structures of all the complexes are fully described and compared here. Moreover, the lone pair−π and π−π noncovalent interactions have been analyzed by means of DFT calculations, mainly focusing our attention to the influence of the coordinating metal on the strength of the interactions and the interplay between hydrogen bonding and π-interactions. We also present here Hirshfeld surface analysis to investigate the close intermolecular contacts.

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presence of various heterocyclic bases (2-amino-4-picoline,2−4,7 2-aminopyridine, 4,8,9 1,10-phenanthroline,5 4-aminopyridine6,11) and organic complexes bearing derivatives of terpyridine ligands.10 During the course of our study, we have noticed several factors like reaction pH, clustering tendency of solvent water molecules, presence of different counteranions, unprecedented dimerization of heteroarenes and several weak forces (π−π, anion−π, lone pair (lp)−π) other than hydrogen bonds, have profound influence on the self-assembly process. We have also provided adequate theoretical support to consolidate our experimental observation further. Our previous reports on salt-bridge (sb)−π9 and lone pair (lp)−salt-bridge (sb)12 interactions has shed considerable light on the interacting ability of salt-bridges (H-bonded arrays)

INTRODUCTION Crystals encapsulate facts about how atoms are arranged to form molecules and molecules interact in between to generate a pristine supramolecular organization. This arrangement of molecules is a spontaneous process called self-assembly and variety of intermolecular forces play key role by mutual interaction. Nevertheless, a systematic study of self-assembly process and intermolecular forces is a prerequisite to achieve control over the organization of molecular components in the solid state, which is also the professed goal of crystal engineering‘‘the designed synthesis of crystals”.1 Our group has shown paramount interest in this aspect during last couple of years. We have intended to provide an atomistic picture of self-assembly process along with the nature of various molecular packing forces, which govern the organization of molecular components in solid state, in both organic and inorganic complexes.2−12 We have studied self-assembly of several metal malonate or nitrilotriacetate complexes in the © 2014 American Chemical Society

Received: October 6, 2014 Revised: November 11, 2014 Published: November 24, 2014 14713

dx.doi.org/10.1021/jp510075m | J. Phys. Chem. B 2014, 118, 14713−14726

The Journal of Physical Chemistry B

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with aromatic rings and even with a lone pair of electron. Such stacking interactions between salt-bridges (H-bonded arrays) and other moieties was scarcely analyzed in the literature and have become fundamental for understanding the structural and functional roles that they play in the self-assembly process. Since anion−π interaction has recently emerged as a new branch of supramolecular chemistry, we believe that, our leading findings (sb−π and lp−salt-bridge interactions) are also extremely promising and will play significant role in the fascinating area of supramolecular chemistry. In addition to these interactions where electron deficient aromatic systems are implicated, other smaller groups like R2CO or RNO2 can also interact favorably with electron-rich molecules by means of their positive π-hole. It has been defined by Murray et al.13 as a region of positive electrostatic potential that is perpendicular to a portion of a molecular framework. It is the counterpart of a σhole, which is along the extension of a covalent bond.14 In a given group of the periodic table, π-holes become more positive on going from the lighter to the heavier atoms and the existence of electron withdrawing groups in the rest of the molecule strongly affects the π-hole magnitude. Positive π-holes interact in a highly directional manner with electron rich molecules, e.g., anions or the lone pairs of Lewis bases.15,16 Hydrogen-bonding involving water molecules along with other noncovalent interactions is capable of guiding the supramolecular self-assembly processes in solid state. In our present study, a discrete water dimer (H2O)2 is also identified in the crystal lattice of complexes 1−5, and we have also described its influence on the resultant supramolecular association. In the present study, five M(II) [M(II) = Ni/Co/Mn/Mg/ Zn] malonate coordination compounds, having identical molecular composition (C6H9N2)4[M(C3H2O4)2(H2O)2](PF6)2·2(H2O) [where C6H9N2 = protonated 3-picoline, C3H4O4 = malonic acid, and PF6− = hexafluorophosphate], have been synthesized and structurally characterized to observe the role of 3-picoline in inducing self-assembly process in both transition and non transition metal complexes. A copper complex namely (C6H9N2)4[Cu(C3H2O4)2](PF6)2 [where C6H9N2 = protonated 3-picoline, C3H4O4 = malonic acid, and PF6− = hexafluorophospahte] has also been synthesized with the aim to investigate subtle changes in the self-assembly processes keeping the reactants unaltered. The self-assembly of complexes 1−5 are found to be identical. Discrete monomeric units [MII(C3H2O4) 2(H2O)2] form 1D chains by selfcomplementary hydrogen bonding. These 1D chains are interlinked side by side to form 2D association along ab direction. A discrete water dimer is found to play important role in constructing this 2D structure. Weaker forces like lone pair−π and π−π interactions involving protonated 3-picoline moieties also helped in building aforesaid 1D chains. The selfassembly of copper complex (6) is different from the others because of its layer structure. In-depth structural analysis of these six metal malonate complexes and plausible structure inducing factors are eventually summarized here. In addition, we have studied by means of high level (BD86-D3/def2TZVP) density functional theory (DFT) methodology the noncovalent interactions observed in the solid state of compounds 1−6. Since the self-assembly of complexes 1−5 is identical, we have studied the effect of the metal on the strength of the CO···CO interactions. An investigation of the close intermolecular contacts between the molecules via Hirshfeld surface analysis is also presented.

Article

EXPERIMENTAL METHODS

Physical Measurements. IR spectra were recorded on a PerkinElmer RXI FT-IR spectrophotometer with the sample prepared as a KBr pellet, in the range 4000−600 cm−1. Elemental analyses (C, H, N) were performed on a PerkinElmer 240C elemental analyzer. Materials. All reactions were carried out in aerobic conditions and with water as the solvent. Malonic acid, copper(II) acetate monohydrate, nickel(II) acetate tetrahydrate, cobalt(II) acetate tetrahydrate, manganese(II) acetate tetrahydrate, magnesium(II) acetate tetrahydrate, zinc(II) acetate dihydrate, 2-amino-3-picoline, and ammonium hexafluorophosphate were used. All chemicals were of reagent grade quality, purchased from Sigma-Aldrich Chemical Co., and used without further purification. Freshly boiled, doubly distilled water was used throughout the present investigation. Synthesis of Compounds 1−5. Nickel(II) acetate tetrahydrate (0.248 g, 1.0 mmol) dissolved in 25 mL of water was allowed to react with malonic acid (0.208 g, 2.0 mmol) in water (25 mL) at 60 °C resulting in a clear green color solution. 4.0 mmol of 2-amino-3-picoline (0.432 g) was added dropwise to the above solution with continuous stirring. Finally, a warm aqueous solution of ammonium hexafluorophosphate (0.652 g, 4.0 mmol) was added to the solution with continuous stirring. The reaction mixture thus obtained was further heated at 60 °C for an hour with continuous stirring. The solution was then cooled to room temperature and filtered and left unperturbed for crystallization. After a few weeks, for 1 block shaped, green single crystals suitable for X-ray analysis were obtained. The crystals were collected by filtration, washed with cold water and dried in air (yield: 65%). Anal. Calcd for C15H24N4F6O6PNi0.5: C, 33.91; H, 4.55; N, 10.55. Found: C, 33.90; H, 4.56; N, 10.54. Main IR absorption bands observed for 1 (KBr pellet, cm−1) are 3752 (s), 3691 (s), 3480 (s), 3209 (b), 2670 (b) 1677 (s), 1595 (s), 1473 (s), 1438 (s), 1364 (s), 1254 (s), 1145 (s), 997 (s), 972 (s), 784 (s), 747 (s). Compound 2 was synthesized using the same procedure as above where we used cobalt(II) acetate tetrahydrate (0.249 g, 1.0 mmol) and the color of the solution was clear pink. After 2 weeks, block shaped, pink single crystals suitable for X-ray analysis were obtained. The crystals were collected by filtration, washed with cold water, and dried in air (yield: 60%). Anal. Calcd for C30H48N8F12O12P2Co: C, 33.91; H, 4.55; N, 10.54. Found: C, 33.90; H, 4.56; N, 10.53. Main IR absorption bands observed for 2 (KBr pellet, cm−1) are 3854 (s), 3625 (s), 3479 (s), 3208 (b), 2670 (b), 1992 (b), 1678 (s), 1594 (b), 1473 (s), 1361 (s), 1254 (s), 997 (s), 843 (b), 784 (s), 728 (s). Compound 3 was synthesized in the same way using Manganese(II) acetate tetrahydrate (0.245 g, 1.0 mmol) to get a colorless solution. After 20 days, block shaped, colorless single crystals suitable for X-ray analysis were obtained. The crystals were collected by filtration, washed with cold water and dried in air (yield: 65%). Anal. Calcd for C15H24N4F6O6PMn0.5: C, 34.03; H, 4.57; N, 10.58. Found: C, 34.01; H, 4.56; N, 10.56. Main IR absorption bands observed for 3 (KBr pellet, cm−1) are 3625 (s), 3584 (s), 3477 (s), 3231 (b), 2709 (b), 1989 (b), 1681 (s), 1472 (s), 1358 (s), 1253 (s), 1146 (s), 997 (s) 842 (b), 746 (s), 722 (s). For compound 4, we used magnesium(II) acetate tetrahydrate (0.214 g, 1.0 mmol), and the solution was colorless. After a few weeks, block-shaped, colorless single crystals suitable for X-ray analysis were obtained. The crystals were collected by 14714


formula M crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg F(000) V/Å3 Z T/K θ min−max/deg λ(Mo Kα)/Å μ(Mo Kα)/mm−1 Crystal Size [mm] R1, I > 2σ(I) (all) wR2, I > 2σ(I) (all) S(GOF) total reflections independent reflections (Rint) observed data [I > 2σ(I)] min and max resd dens [e/Å3]

2 C30H48N8O12 P2F12Co 1061.63 triclinic Pı ̅ (No. 2) 7.1481(6) 11.5208(11) 13.9059(13) 86.246(3) 76.498(3) 75.782(3) 545 1079.38(17) 1 100 1.5−28.4 0.71073 0.590 0.08 × 0.17 × 0.20 0.0538 0.1577 1.09 5031 5031 3961 −0.67, 0.89

1

C30H48N8O12 P2F12Ni 1061.39 triclinic Pı ̅ (No. 2) 7.0869(5) 11.5189(8) 13.9132(9) 86.240(2) 76.457(2) 76.180(2) 546 1072.18(13) 1 100 1.5−30.1 0.71073 0.646 0.05 × 0.10 × 0.20 0.0358 0.0940 0.99 13459 5354(0.027) 4518 −0.33, 0.46

Table 1. Crystallographic data for Compounds 1−6 C30H48N8O12 P2F12Mn 1057.44 triclinic Pı ̅ (No. 2) 7.2720(5) 11.5596(7) 13.8989(9) 85.380(2) 76.438(2) 74.896(2) 543 1096.31(12) 1 100 1.8−30.4 0.71073 0.491 0.20 × 0.25 × 0.40 0.0473 0.1259 1.05 10444 5655(0.026) 4739 −0.52, 0.86

3 C30H48N8O12 P2F12Mg 1027.01 triclinic Pı ̅ (No. 2) 7.1432(7) 11.5494(9) 13.8681(12) 86.818(3) 76.679(3) 76.156(3) 530 1080.99(17) 1 100 1.8−30.3 0.71073 0.234 0.10 × 0.15 × 0.35 0.0439 0.1221 1.07 13314 5657(0.042) 4404 −0.39, 0.47

4 C30H48N8O12 P2F12Zn 1068.07 triclinic Pı ̅ (No. 2) 7.2090(7) 11.6545(11) 14.1210(14) 86.113(4) 75.849(5) 76.450(4) 544 1118.32(19) 1 302 2.3−30.4 0.71073 0.735 0.24 × 0.36 × 0.74 0.0524 0.1586 1.05 18357 6186(0.048) 4887 −0.54, 0.60

5

C30H40N8O8P2F12Cu 994.19 monoclinic C2/m (No. 12) 12.330(2) 18.095(3) 8.7426(17) 90 96.627(7) 90 1014 1937.5(6) 2 100 2−29.8 0.71073 0.764 0.12 × 0.15 × 0.25 0.0645 0.1843 1.21 2570 2570 1931 −1.06, 1.13

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filtration, washed with cold water and dried in air (yield: 70%). Anal. Calcd for C30H48N8F12O12P2Mg: C, 35.05; H, 4.71; N, 10.90. Found: C, 35.03; H, 4.73; N, 10.91. Main IR absorption bands observed for 4 (KBr pellet, cm−1) are 3861 (s), 3742 (s), 3626 (s), 3479 (s), 3207 (b), 1989 (b), 1681 (s), 1471 (s), 1372 (s), 1254 (s), 1146 (s), 996 (s), 838 (b), 728 (s). Compound 5 was also synthesized accordingly using Zinc(II) acetate dihydrate (0.219 g, 1.0 mmol) and the solution was colorless. After 2 weeks, prism shaped, colorless single crystals suitable for X-ray analysis were obtained. The crystals were collected by filtration, washed with cold water and dried in air (yield: 60%). Anal. Calcd for C30H48N8F12O12P2Zn: C, 33.70; H, 4.53; N, 10.48. Found: C, 33.71; H, 4.55; N, 10.50. Main IR absorption bands observed for 5 (KBr pellet, cm−1) are 3626 (s), 3479 (s), 3218 (b), 2000 (b), 1681 (s), 1473 (s), 1435 (s), 1361 (s), 1274 (s), 1254 (s), 1146 (s), 997 (s), 843 (b), 747 (s), 727 (s). Synthesis of Compound 6. Compound 6 was also synthesized using the same procedure as above. Copper(II) acetate monohydrate (0.199 g, 1.0 mmol) dissolved in 25 mL of water was allowed to react with malonic acid (0.208 g, 2.0 mmol) in water (25 mL) at 60 °C resulting in a clear blue solution. 4.0 mmol of 2-amino-3-picoline (0.432 g) was added dropwise to the above solution with continuous stirring. Finally a warm aqueous solution of ammonium hexafluorophosphate (0.652 g, 4.0 mmol) was added to the solution with continuous stirring. The reaction mixture thus obtained was further heated at 60 °C for an hour with continuous stirring. The solution was then cooled to room temperature and filtered and left unperturbed for crystallization. After a few weeks, for 6 block shaped, blue single crystals suitable for X-ray analysis were obtained. The crystals were collected by filtration, washed with cold water and dried in air (yield: 60%). Anal. Calcd for C15H20N4O4F6PCu0.5: C, 36.21; H, 4.05; N, 11.26. Found: C, 36.25; H, 4.01; N, 11.20. Main IR absorption bands observed for 6 (KBr pellet, cm−1) are 3840 (s), 3691 (s), 3459 (s), 3363 (s), 3144 (s), 1659 (s), 1574 (s), 1469 (s), 1409 (s), 1378 (s), 1280 (s), 1256 (s), 1142 (s), 1048 (s), 985 (s), 836 (m), 770 (s), 743 (s). Theoretical Methods. The energies of all the species included in this study were computed at the BP86-D3/def2TZVPD level of theory using the crystallographic coordinates within the program TURBOMOLE version 6.4.17 The interaction energies were calculated with correction for the basis set superposition error (BSSE) by using the Boys− Bernardi counterpoise technique.18 For the calculations we have used the BP86 functional with the latest available correction for dispersion (D3). The “atoms-in-molecules” (AIM)19 analysis was performed at the BP86/def2-TZVP level of theory. The calculation of AIM properties was done using the AIMAll program.20 X-ray Crystal Structure Determination of Complexes 1−6. Crystallographic data for 1−6 were collected at 100(2) K on a Bruker Kappa APEX II DUO diffractometer equipped with an APPEX 2 4K CCD area detector and a microsource with Mo Kα radiation (λ = 0.71073 Å). The raw frame data were processed using SAINT and SADABS to yield the reflection data file.21 The structures were solved by Direct Methods using SIR201122 and refined on Fo2 by full-matrix least-squares procedures, using SHELXL-97.23 Data collection and refinement parameters for complexes 1−6 are summarized in Table 1. Non-H atoms were refined anisotropically and H atoms were introduced in calculated positions and refined riding on their

parent atoms, except for those corresponding to water molecules, which were located in the difference Fourier maps. The restraints applied in the refinement of the structures 1−3 are as follows: the anion (PF6−) has been modeled as disordered, restraining the bond distances to be the same for the two positions of the anion. In addition, the anisotropic displacement parameters for this anion were also restrained. Finally, the H−O bond distances of the water molecules were restrained.

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RESULTS AND DISCUSSION Crystal Structure Description of Complexes 1-5. The complexes 1−5 are essentially isomorphous and crystallized in the triclinic space group Pı ̅ with the asymmetric unit consisting of half of the molecular anion [MII(C3H2O4)2(H2O)2]2−, two crystallographically independent C6H9N2+ cations, one distorted hexafluorophosphate as counteranions and a distorted water molecule. The full anion is generated by the symmetry operation of an inversion center. Perspective view of a representative asymmetric unit of complexes 1−5 is shown in Figure 1. Selected bond lengths, angles and supramolecular

Figure 1. Representative ORTEP diagram for complexes 1−5. The unlabeled atoms are generated by the inversion operation.

interactions for complexes 1−5 are listed in Tables S1−S10 and Tables 2−4. In all the complexes, M(II) ions, are located on an inversion center, and possess an octahedral coordination environment whose equatorial planes are formed by the oxygen atoms O1 and O3 from the malonate units and their symmetry related counterparts O1**, O3** (** = 1 − x, 1 − y, 1 − z for 1, −x, 1 − y, 1 − z for 2, 1 − x, 2 − y, 1 − z for 3, −x, 1 − y, −z for 4 and 2 − x, 2 − y, −z for 5) from the second malonate units. Two water molecules (O5 and O5**, (** = 1 − x, 1 − y, 1 − z for 1, −x, 1 − y, 1 − z for 2, 1 − x, 2 − y, 1 − z for 3, −x, 1 − y, −z for 4 and 2 −x, 2 − y, −z for 5) occupy the trans axial positions, thus generating a MO4O/2 chromophore. The M−O bond distances in the equatorial plane vary between 2.0 and 2.12 Å for complexes 1−5. The values of the apical M−O(5) bond lengths in 1−5 vary between 2.109(15) and 2.2576(13) Å, which are longer than the equatorial bond distances and suggesting that the coordination polyhedron of the M(II) atoms in the anionic units is a slightly distorted octahedron. All coordination bonds and angles in the anionic unit are within the range of values previously observed for related malonatecontaining complexes.8 Malonate ligands usually adopt an envelope conformation in which only the methylene group is 14716



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Table 2. Geometrical Parameters (Å, deg) for Intermolecular Carbonyl···Carbonyl Interactions in Complexes 1−5

complex

A1 (deg)

A2 (deg)

A3 (deg)

A4 (deg)

D1 (Å)

D2 (Å)

torsion angle τ (deg)

1 2 3 4 5

93.74 93.74 93.82 93.58 90.97

86.26 86.26 86.18 86.42 89.03

93.74 93.74 93.82 93.58 90.97

86.26 86.26 86.18 86.42 89.03

3.13 3.16 3.16 3.15 3.18

3.13 3.16 3.16 3.15 3.18

0 0 0 0 0

CO---CO configuration planar planar planar planar planar

antiparallel antiparallel antiparallel antiparallel antiparallel

Table 3. Geometrical Parameters (Å, deg) for Lone Pair−π Interactions in 1−5a Y−X(I)---Cg(J)

X---Cg

Y---Cg

Y−X---Cg

X−Perp

symmetry

C(1)−O(2)---Cg(3) C(1)−O(2)---Cg(3) C(1)−O(2)---Cg(4) C(3)−O(4)---Cg(1) C(1)−O(4)---Cg(4)

3.189(18) 3.195(2) 3.196 (2) 3.176 (2) 3.295(3)

4.14(2) 4.143(3) 4.150(2) 4.113(2) 4.216(3)

132.1(13) 132.2 (2) 132.6(1) 130.8(1) 130.9(2)

3.034 3.036 3.028 3.036 3.129

1 − x, 1 − y, 1 − z x, y, z x, y, z x, y, z 1 − x, 1 − y, −z

a

Cg(J) denotes centroid of the jth ring.Complex 1: Ring(3) [N(1A)/C(1A)/C(2A)/C(3A)/C(4A)/C(5A)]. Complex 2: Ring(3) [N(1A)/C(1A)/ C(2A)/C(3A)/C(4A)/C(5A)]. Complex 3: Ring(4) [N(1C)/C(1C)/C(2C)/C(3C)/C(4C)/C(5C)]. Complex 4: Ring(1) [N(1A)/C(1A)/ C(2A)/C(3A)/C(4A)/C(5A)]. Complex 5: Ring(4) [N(3)/C(10)/C(11)/C(12)/C(13)/C(14)].

Table 4. Geometrical Parameters (Å, deg) for π···π Interactions in 1−5a Cg(I)a −Cg(J)

Cg ---Cg

dihedral angle

symmetry

→ → → → →

3.587(14) 3.602(2) 3.647(2) 3.596(1) 3.667(2)

5.9(12) 5.4(2) 4.1(1) 5.8(1) 5.5(2)

2-X,1-Y,1-Z 1-X,1-Y,1-Z 1+X,Y,Z X,Y,Z X,Y,Z

Cg(3) Cg(3) Cg(3) Cg(1) Cg(3)

Cg(4) Cg(4) Cg(4) Cg(2) Cg(4)

Figure 2. Left: Formation of 1D tape in complexes 1−5 through association of discrete [MII(C3H2O4)2(H2O)2]2− monomeric units. The occurrence of hydrogen bonding interactions (dotted brown lines) along the a axis generates a R22(12) cyclic motif. Intermolecular carbonyl···Carbonyl antiparallel stacking (dotted blue lines) also come into play. Color code: M(II), green; O, red; C, light purple; hydrogen, aquamarine.

a

Cg(I) denotes centroid of the ith ring. Complex 1: Ring(3) [N(1A)/ C(1A)/C(2A)/C(3A)/C(4A)/C(5A)]; ring(4) [N(1B)/C(1B)/C(2B)/C(3B)/C(4B)/C(5B)]. Complex 2: Ring (3) [N(1A)/C(1A)/ C(2A)/C(3A)/C(4A)/C(5A)]; ring (4) [N(1B)/C(1B)/C(2B)/C(3B)/C(4B)/C(5B)]. Complex 3: Ring (3) [N(1A)/C(1A)/C(2A)/ C(3A)/C(4A)/C(5A)]; ring (4) [N(1C)/C(1C)/C(2C)/C(3C)/ C(4C)/C(5C)]. Complex 4: Ring (1) [N(1A)/C(1A)/C(2A)/ C(3A)/C(4A)/C(5A)]; ring (2) [N(1B)/C(1B)/C(2B)/C(3B)/C(4B)/C(5B)]. Complex 5: Ring (3) [N(1)/C(4)/C(5)/C(6)/C(7)/ C(8)]; ring (4) [N(3)/C(10)/C(11)/C(12)/C(13)/C(14)].

tions24,25 play crucial roles in organic and biological systems largely due to its ubiquitous presence. Present studies also revealed that this interaction is well recognized in small molecules and protein− ligand complexes and demand further attention for a systematic study. The geometrical parameters for this planar antiparallel intermolecular interaction of carbonyl groups are summarized in Table 2. The distance between C---O is well below their corresponding van der Waals radii (3.22 Å) indicating moderate interaction energy. The energetic features of this interaction including the effect of the hydrogen bonding interactions involving the coordinated water molecules are further analyzed below in the theoretical study. Each monomeric anionic unit of complexes 1−5 recognizes four aminopicolinium cations (C6H9N2+) through doubly coordinated carboxylate ends and also through employing

significantly displaced from the chelate ring plane and the present examples are also in-line with this generalization.8 The monomeric anionic units, i.e., [MII(C3H2O4)2(H2O)2]2− are interlinked to each other via strong self-complementary hydrogen bonds which give rise to a R22(12) cyclic motif, ultimately generating an infinite 1D tape along the crystallographic a axis (Figure 2). We notice an interesting intermolecular antiparallel stacking of carbonyl groups of malonate moieties between monomeric units (Figure 2). This intermolecular carbonyl---carbonyl (CO---CO) interac14717



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apical oxygen atoms (Figure 3), leading to R22(8) hydrogen bonding assemblies involving various hydrogen bonds (see

Figure 4. 1D tapes are interlinked side by side by discrete water dimer along b axis. Viewed along a axis. Color code: M(II), green; O, red; N, blue; C, light purple; H, aquamarine.

Figure 3. Each monomeric unit of complexes 1−5 is also connected to four 3-aminopicolinium cations through the formation of R22(8) cyclic motifs. The chain is viewed along the b axis. Color code: M(II), green; O, red; N, blue; C, light purple; hydrogen, aquamarine.

respective tables for complexes 1−5). Two dangling hexafluorophosphate counteranions are also attached with monomeric units through hydrogen bonds involving fluorine atoms (see respective tables for hydrogen bonds). The noncoordinating carbonyl oxygen atoms O2/O4 of the malonate moieties in complexes 1−5 are orientated toward the π-face of aminopicoline rings (Figure 3). The angles with which these carbonyl oxygen atoms (O2/O4) approach the π-face of the aminopicoline ring reflect significant lone pair−π interaction.8 Geometric parameters of such lone pair−π interactions are summarized in Table 3 and shown in Figure 3. Such aminopicoline rings are further stacked over second aminopicoline molecules to form lone pair−π/ π−π associations, which is shown in Figure 3. Details of these π−π interactions in complexes 1-5 are summarized in Table 4. These coupled lone pair−π and π−π interactions within the monomeric units also assist the formation of a 1-D tape (Figure 3). Water, due to its strong hydrogen bonding ability as well as coordination capability is often incorporated into the metal− organic frameworks (MOFs) in the form of monomer, dimer and various higher order oligomers.3 In our case, a discrete water dimer has been identified in the crystal lattice of complexes 1−5 and it plays an important role by stitching aforementioned 1D tapes to generate a 2D network along b axis (Figure 4). Such small water clusters, [(H2O)n, n = 2−10], have attracted much attention from both theoretical and experimental aspects, because they help in understanding structure and characteristics of bulk water or ice and are well documented in the literature.26−28 In this context, the work of Saykally and co-workers is worth mentioning.28 In our case, Two water molecules form a near linear supramolecular water dimer with average O---O distance being 2.8476 Å in complexes 1−5. For comparison, the corresponding values in regular ice, in liquid water, and in the vapor phase are 2.74,

Figure 5. Overall 3D packing of complexes 1−5. Viewed along a axis. Color code: M(II), green; O, red; N, blue; C, light purple; hydrogen, aquamarine; phosphorus, orange; fluorine, light green.

2.85, and 2.98 Å, respectively.26−28 Overall 3D packing (Figure 5) is achieved by various hydrogen bonds in 1−5. Crystal Structure Description of Complex 6. Complex 6 crystallized in the monoclinic space group C2/m and its structure consists of C6H9N2+ cations, [Cu(C3H2O4)2]2−, and hexafluorophosphate anions. Perspective view of the asymmetric unit of complex 6 is shown in Figure 6. Selected bond lengths, angles and supramolecular interactions for 6 are listed in Tables S11 and S12. In 6, the four-coordinated Cu(II) ion is located on a 2/m crystallographic site. The equatorial plane is formed by the oxygen atoms from the malonate units. All

Figure 6. ORTEP diagram of 6 with 50% ellipsoidal probability. Only selected atoms are numbered for clarity. Color code: Cu (II), green; O, red; N, blue; C, light purple; fluorine, light green; phosphorus, orange. 14718



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coordination bonds and angles in the anionic unit are within the range of values previously observed for related malonatecontaining complexes.4,8,12 The key difference of compound 6 with respect to the compounds described above is that the metal ion is four-coordinated. It is well-known29 that for Cu(II) complexes there is an energy advantage for square-planar complexes with both strong- and weak-field by taking into consideration the orbital energy levels. Each monomeric anionic unit, i.e., [Cu(C 3 H 2 O 4 ) 2 ] 2− recognizes four aminopicolinium cations (C6H9N2+) through doubly coordinated carboxylate ends leading to R22(8) hydrogen bonding assemblies involving the hydrogen bonds N2A−H2A1---O2 and N1A−H1A---O1. Monomeric anionic units are interlinked through aminopicolinium cations via N2A−H2A2---O2 and N2A−H2A1---O2 hydrogen bonds forming a 2D sheet like appearance which grows along ab plane (Figure 7). Copper atoms lie on such planes forming an

Figure 8. Interdigitation of 2D layers through π−π interactions in 6. This assembly is viewed along the b axis. Color code: Cu (II), green; O, red; N, blue; C, light purple; hydrogen, aquamarine; phosphorus, orange; fluorine, light green.

Figure 7. Two-dimensional assembly of monomeric units of 6. This assembly is viewed along the c axis. Color code: Cu (II), green; O, red; N, blue; C, light purple; hydrogen, aquamarine.

Figure 9. P−F---CO (anion---π−hole) interactions in 6. This assembly is viewed along the b axis. Color code: Cu (II), green; O, red; N, blue; C, light purple; hydrogen, aquamarine; phosphorus, orange; fluorine, light green.

overall layered structure for 6 and layers are interlinked through π−π interactions [for complex 6, R(1) = N(1A)/C(1A)/ C(2A)/C(3A)/C(4A)/C(5A)’ symmetry code, 2 − x, y, 2 − z; centroid-to-centroid distance, 3.783(2) Å] among aminopicolinium moieties (Figure 8). Although metal atoms lie on the plane, malonate ligands are shifted significantly from these metal planes. Aminopicolinium ligands are organized in such a manner that it protrude out of the plane on both side facilitating the stacking of successive sheets through π−π interactions. One fluorine atom of PF6− group is interacting with the carbonyl carbon of malonate moiety resulting in fluoride carbonyl P−F---CO (anion---π−hole) interactions (Figure 9). The shortest separation distance between F(3)--C(1) is 2.818(4) Å, which is also well below their corresponding van der Waals radii (3.17 Å) indicating fairly strong association. A recent survey30 has revealed that such fluoride carbonyl short interactions are rare and in our case this interaction is the first report where an isolated PF6− group is interacting with the carbonyl carbon of a malonate moiety. This issue has been further studied below. Theoretical Study. We have focused the theoretical study to the analysis of the relevant noncovalent interactions (vide supra) observed in the solid state architecture of compounds 1−6. As aforementioned, in the isostructural compounds 1−5 antiparallel CO---CO interactions are implicated in the

crystal packing through the formation of 1D infinite tapes, which are assembled by means of the association of discrete [MII(C3H2O4)2(H2O)2]2− monomeric units (see Figure 2). Obviously the association of these dianionic discrete units should be repulsive due to electrostatic forces. The influence of the countercation (protonated aminopyridine) is crucial to stabilize the assembly. We have used a neutral model where one malonate ligand has been replaced by malonic acid (see Figure 10). The model is shown in Figure 10A and the interaction energies for the self-assembly of two [MII(C3H2O4)(C3H4O4)(H2O)2] units are large and negative for all compounds (from −24.1 to −19.9 kcal/mol), indicating a strong binding, which is basically due to the formation of two strong OW−H---O hydrogen bonds. In order to estimate the contribution of the individual CO---CO interaction we have used an additional theoretical model where the water molecules and metal ions have been eliminated. Consequently, the interaction energy (denoted as ΔEa, see Figure 10B) is considerably reduced to approximately −2 kcal/mol for all complexes (we have used the crystallographic coordinates for the calculations). Therefore, the contribution of the antiparallel CO stacking is modest, in agreement with previous studies,24,25 and the formation of 1D infinite tape is basically supported by the hydrogen bonding interactions. We have computed an 14719



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close examination of the assembly reveals that one aminopyridine ring is establishing a salt-bridge interaction with one malonate of the [MII(C3H2O4)2(H2O)2]2− moiety and the other aminopyridine is also forming a pseudo-salt-bridge interaction with the malonate and coordinated water molecule of the dianion. Therefore, we have also included two formate anions as counterions to simulate the effect of malonate in the assembly (see Figure 11). As a result we have obtained

Figure 11. Left: X-ray fragment modeled in the theoretical study to analyze the anion−π/π−π assembly. Right: Theoretical models used to evaluate the interaction of the assembly.

favorable interaction energy for the assembly (ΔE6 = −9.3 kcal/ mol), which is more favorable than the sum of the individual anion−π (ΔE8 = −0.3 kcal/mol) and π−π complexes (−5.7 kcal/mol) indicating a favorable interplay between both interactions. Because of the significant approximations we have done in the theoretical model, a quantitative and direct correlation between the theoretical interaction energies and the solid state structure is premature. However, the favorable mutual influence between both interactions observed theoretically is relevant and likely suggests the existence of favorable cooperativity effects in the solid state. The origin of the favorable interplay between both interactions likely comes from the polarization of one π-system as a consequence of the interaction with the other one that enhances the ability of the ring for the interaction with the electron rich molecule. This is corroborated by the molecular electrostatic potential (MEP) analysis computed for the protonated 3-picoline−formate complex and its π-stacked dimer (see Figure 12). The MEP

Figure 10. Theoretical models used to evaluate the CO---CO interaction in compounds 1−5.

additional theoretical model for each compound in order to study the influence of the hydrogen bonded water molecule on the CO---CO interaction. The interaction energies (denoted as ΔEb, see Figure 10B) of these complexes have been computed as dimers where the H-bonded water is part of the monomer. The binding energies range from −11.3 to −10.3 kcal/mol indicating that the water molecule has a strong influence of the interaction energy likely due to the enhanced polarization of the CO bond favoring the dipole−dipole interaction. Finally, we have also evaluated the effect of the peripheral COOH group on the interaction energies since there is a repulsive interaction between the central CO group of one molecule and the peripheral COOH group of the other. Therefore, two additional models have been computed (see Figure 10D,E) where the peripheral COOH group has been changed by hydrogen atom. As a result the interaction energies denoted as ΔEc and ΔEd are more negative than the respective ΔEc and ΔEd energies, indicating that the antiparallel CO--CO interaction (free from other influences) ranges from −3.2 to −3.1 kcal/mol. Furthermore, the influence of the Hbonded water molecule that enhances the dipole−dipole interaction is approximately −11 kcal/mol. Another interesting aspect that we have analyzed by means of DFT calculations is the formation of the lp−π/π−π assembly described in Figure 3. The lone pair donor atom belongs to the [MII(C3H2O4)2(H2O)2]2− moiety and consequently the anionic nature of the interacting atom likely enhances the strength of the interaction. Another consideration is that the π-system is a protonated aminopyridine ring that also contributes to the enhancement of the lp−π interaction. However, this is only one part of the assembly and the other part involves the formation of a stacking complex between two protonated rings and consequently a strong electrostatic repulsion is expected. A

Figure 12. Molecular electrostatic potential of the 3-picoline−formate salt-bridge (A) and the dimer (B).

surface of the protonated 3-picoline−formate complex (Figure 12A) shows a positive potential over the center of the ring that is 20 kcal/mol. In addition, if the MEP surface is plotted in the dimer (Figure 12B), the electrostatic potential measured at the same point increases to from 20 to 28.7 kcal/mol. Therefore, the π-acidity of the 3-picoline ring is enhanced by the presence 14720



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Figure 13. Left: X-ray fragment modeled in the theoretical study to analyze the anion---π−hole interaction. Right: Theoretical models used to evaluate the interaction and the molecular electrostatic surface (MEPS) of malonic acid with indication of the π-hole. Distances are in Å.

Figure 14. (A) MEP Surface of a model of compound 6: (C6H9N2)4[Cu(C3H2O4)2]. (B) NCI plot of a fragment of compound 6. The NCI plot only shows intermolecular itneractions.

of the other π-stacked picoline ring thus favoring the interaction with the anion. With respect to compound 6, we have analyzed theoretically the interesting π-hole interaction (PF6−---CO) observed in the solid state of compound 6 that has been highlighted previously in Figure 9. One fluorine atom of the anion establishes a bifurcated interaction with the carbon atoms that belong to the coordinated carboxylate groups of malonate. The X-ray fragment and theoretical models used are shown in Figure 13. We have computed the interaction energy in a large fragment of the X-ray structure consisting of a [CuII(C3H2O4)2]2− moiety interacting with two aminopyridine counterions (see Figure 13B). The interaction energy of this assembly (C6H9N2)2[CuII(C3H2O4)2] with PF6− is ΔE9 = −20.8 kcal/mol, indicating a strong interaction. However, there is a contribution that simply arises from the interaction of the anion with the protonated aminopyridine rings and the Cu(II). We have also computed another model (see Figure 13C) where the Cu(II) and pyridine have not been considered and only one malonic acid is used. As a result the interaction energy is reduced to ΔE9 = −6.1 kcal/mol that corresponds to the contribution of the bifurcated PF6−---CO interaction. We have computed the molecular electrostatic potential surface (MEPS) of malonic acid in the conformation that it adopts in the X-ray structure and the π-hole can be clearly appreciated. Very interestingly, the position of the fluorine atom of the PF6− that participates in the bifurcated PF6−---CO interaction is located exactly over the π-hole region shown in the MEPS, stressing the importance of this contribution to the final architecture in the solid state of compound 6. In the discussion of the π-hole interaction we have used a neutral model (malonic acid, see Figure 13C) to evaluate the contribution of the interaction to the binding energy of the assembly shown in Figure 13B. However, in the solid state the

malonate ligand is not neutral and it is coordinated to the Cu ion. Therefore, we have further analyzed this interaction using a more elaborated model. That is, to examine if the π-hole is also observed in the MEP surface of the CuII-coordinated malonate we have used a model that includes a [Cu(C3H2O4)2]2− moiety and two protonated 3-picoline counter cations. Interestingly, the MEP surface in this more realistic model also shows a welldefined positive region where the electrostatic potential is positive (+3.5 kcal/mol, see Figure 14A). We have also computed the atomic partial charges derived from electrostatic potential by using the Merz−Kollman (MK)31 method since it provides high quality charges.32 The MK charges of the malonate are −0.55 and −0.64 e for the oxygen atoms, +0.70 e for the sp2 carbon atom and −0.45 e for the sp3 carbon atom. Therefore, the origin of the π-hole is clearly related to the distribution of the atomic partial charges of the malonate ligand. Moreover, we have used the noncovalent index (NCI) method33−35 to study the anion---π-hole observed in the X-ray structure model represented in Figure 13B. This method relies on two scalar fields to map local bonding properties: the electron density (ρ) and the reduced-density gradient (RDG, σ). It is able of mapping real-space regions where noncovalent interactions are important and is based exclusively on the electron density and its gradient. The information provided by NCI plots is essentially qualitative, i.e. which molecular regions interact. The color scheme is a red-blue scale with red for ρ+cut (repulsive) and blue for ρ−cut (attractive). Moreover, green and yellow isosurfaces correspond to weakly attractive and weakly repulsive interactions, respectively. It is remarkable to note that the NCI plot analysis shows a clear green isosurface (see Figure 14B) that characterizes anion---π-hole, which covers both sp2 carbon atoms of the malonate ligands and coincides with the positive electrostatic region observed in the MEP surface (Figure 14A). 14721



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Figure 15. AIM analysis of several assemblies found in the solid state of compounds 1−6. Bond, ring, and cage critical points are represented by red, yellow, and green spheres, respectively. The bond paths connecting bond critical points are also represented by dashed lines.

Figure 16. Partial view of the X-ray structures of QACVAR, NUZZIS and JERMEY. Distances are in Å. Some hydrogen atoms are omitted for clarity.

Finally, we have used the Bader’s theory of “atoms in molecules”, which provides a convenient definition of chemical bonding,19 to further describe the noncovalent interactions presented above. The AIM theory has been successfully used to characterize and understand a great variety of interactions; therefore it is adequate to analyze the new interactions described above. In Figure 15 we show the AIM analysis of the anion−π/π−π assembly and antiparallel CO---CO interactions of compounds 1−5 and the anion---π−hole in compound 6. For the anion−π/π−π assembly, the anion−π interaction is characterized by the presence of one bond critical point that connects the oxygen atom with the nitrogen atom of the aminopyridine ring. In addition a bond critical point connects the anion with the oxygen atom of the formate that is used as counterion of the protonated aminopyridine. It should be mentioned that the presence of a bond critical points connecting two atoms does not mean that the binding is favorable; it only indicates that there is an interaction. Obviously, this O---O interaction between two formate units is electrostatically unfavorable, and it is responsible for the very modest anion−π binding energy (ΔE8 = −0.3 kcal/mol, see Figure 11). The π−π stacking interaction is characterized by the presence of three bond critical points (red spheres) that connect the two pyridine moieties. The stacking interaction is further characterized by the presence of several ring critical points (yellow spheres) and cage critical points (green

spheres). The antiparallel CO---CO interaction is characterized by the presence of two bond critical points that connect the oxygen atoms with the carbon atoms. As a consequence a ring critical point is also generated that further characterizes this interaction. The anion···π−hole interaction is characterized by the presence of three bond critical points that connect one fluorine atom with two carbon atoms of malonate and another fluorine atom with the Cu metal ion. The value of the Laplacian of the charge density computed at the bond critical points for all systems studied is positive, as is common in closed-shell interactions. CSD Analysis. We have performed several searches in the Cambridge Structural Database (CSD) in order to further analyze the bifurcated PF6−---CO interaction observed in compound 6. It is well-known that the CSD is a convenient and reliable tool for analyzing geometrical parameters. We have first searched anion−π-hole interactions between any anion and malonate coordinated to any transition metal. As a result, we have not found any hit, indicating that the π-hole interaction observed in compound 6 between malonate and PF6− is unprecedented. However, if the search is extended to derivatives of malonate, three hits are obtained (see Figure 16). In two of them (QACVAR and NUZZIS), the anion is hexafluoroantimonate and the malonate-based ligand is neutral (diethyl isopropylidenemalonate in NUZZIS and dimethyl 2benzylidenemalonate in QACVAR). Finally, the third example 14722



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Figure 17. Number of hits from the different CSD searches. Some examples are shown. Distances are in Å.

relevance to the anion−π-hole binding mode and can be exploited as new supramolecular synthon in chemistry. Indeed, in case of malonate such structures represent a unique electrophilic bowl that can accommodate a range of electron rich molecules. Hirshfeld Surface Analysis. Molecular Hirshfeld surface36−40 in the crystal structure is constructed based on the electron distribution calculated as the sum of spherical atom electron densities.41,42 The normalized contact distance (dnorm) based on both de and di, and the vdW radii of the atom, given by eq 1 enable identification of the regions of particular importance to intermolecular interactions.36 The combination of de and di in the form of a 2D fingerprint plot43,44 provides summary of intermolecular contacts in the crystal.36 The Hirshfeld surface is mapped with dnorm and 2D fingerprint plots presented here was generated using CrystalExplorer 2.14.45

involves a dianionic ligand (2-methylmalonate) and the interacting anion is chloride. In this case the location of the anion in the X-ray fragment shown in Figure 16 (right) is basically due to the H-bond interaction with the ammonia group and some contribution of the anion−π-hole interaction. Since the aforementioned searches were restricted to coordinated malonate (or derivative) establishing bifurcated X−---(CO)2 interactions, we have expanded the search to any coordinated carboxylate based ligand establishing a π-hole interaction with an anion. The results are gathered in Figure 17 and a significant number of hits have been found. We have divided the searches depending on the type of anion used. We have found 123 hits for oxoanions, 47 hits for halides, and 25 hits for fluorine based anions. Some selected examples are shown in Figure 17 and most of them are characterized by short X−---CO distances (in some cases considerably shorter than the sum of van der Waals radii). This considerably amount of structures exhibiting interactions between anions and the πhole of a carboxylate group coordinated transition-metal gives

dnorm =

di − rivdw rivdw

+

de − revdw revdw

(1)

The Hirshfeld surfaces of the title complexes were analyzed for the clarification of the intermolecular interactions involved within the structures and the dnorm surfaces are depicted in Figure 18. The associated fingerprint plots, which summarize the intermolecular interactions, are depicted in Figure 19. The information included in the hydrogen bonding tables are clearly evidenced by the spots on the dnorm surfaces. The large circular depressions visible on the dnorm surfaces are the indicators of dominant O−H---O interactions whereas other light visible spots are due to H---H contacts. The small extent of area and light color on the surface indicate weaker and longer contacts other than hydrogen bonds. The anionic metal-malonate moieties have been considered for the Hirshfeld surface analyses of each complex and hence the fingerprint plots are quite asymmetric. The Hirshfeld surfaces do not show similar proportions of O···H/H---O interactions for the title complexes. The O---H interactions are designated by the spikes in the donor region of the fingerprint plots and show that the metal coordinated water oxygen atoms are in contact with the carbonyl oxygen atoms of the malonate moieties (Figure 19). On the contrary, the H···O interactions which are represented by the spikes in the acceptor region are mainly due

Figure 18. Hirshfeld surfaces mapped with dnorm for the title complexes 1−6. 14723



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Figure 19. Fingerprint plots of the complexes 1−6 showing the percentages of contacts contributed to the total Hirshfeld surface area.

Figure 20. Relative contributions of various intermolecular contacts to the Hirshfeld surface area in complexes 1−6.

analysis of the fingerprint plots shows the one sharp spike arises due to metal M(II)---O interaction for the title complexes which varies from 8.2% in 1 to 14.5% of the total Hirshfeld surface area in 6 (Figure 18). The breakdown plots for the metal-O contribution have been included in Figure S2. There is no F---H contribution to the Hirshfeld surface of each molecule in 1−6. The Hirshfeld surface analysis does not show a similar proportion of H---F interactions for each molecule, ranging from 6.9% in 6 to 11.2% in 4. The breakdown plots are depicted in Figure S3. No significant difference between the molecular interactions in terms of H---H contacts are reflected in the distribution of scattered points in the fingerprint plots (Figure S4) of the title complexes which varied from 19.1% in 5

to N−H---O interactions. A close inspection of the fingerprint plots show that the O---H interactions have larger variation than the H---O interactions. Quantitative insight of the fingerprint plots shows that O---H interaction varies from 28.0% in 6 to 39.8% in 2 and 3 whereas the O---H interaction varies from 1.5% in 6 to 8.4% in 5. Thus, the total O---H/H--O interaction ranges from 29.6% in 6 to 45.6% in 3. The fingerprint plots have been decomposed to emphasize particular atom pair close contacts which facilitates the separation of contributions from diverse interaction types, which overlap in the full fingerprint. The decomposed fingerprint plots corresponding to O---H/H---O contribution in the Hirshfeld surfaces are depicted in Figure S1. A critical 14724



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Notes

to 22.0% in 1. No major C---H contributions were observed in the title complexes which varied from 0.7% in 3 to 3.5% in 6 and these minor contributions to the Hirshfeld surfaces have been depicted by the breakdown fingerprint plots in Figure S5. Moreover, the Hirshfeld surface of the complexes comprises O---C/C---O and O---F/F---O contacts which are depicted in Figure S6 and Figure S7 respectively. Figure 20 contains the percentages of contributions for a variety of contacts in the compounds 1−6. From these values, one can see that the other interactions are minimal in 4 (only 5.9% of the total Hirshfeld surface area compared with 6.2%, 6.3%, 6.2%, 9.8%, and 20.4% in 1, 2, 3, 5 and 6, respectively). This quantitatively authenticated observations display the effectiveness of Hirshfeld surface to gain insights into the intermolecular interactions.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS M.M. gratefully acknowledges the University Grants Commission (New Delhi) for a senior research fellowship. P.M. thanks the Council of Scientific and Industrial Research (New Delhi, India) for a senior Research Fellowship (09/096 (0641) 2010EMR-I). S.M. is grateful to the UPE II programme of the Jadavpur University sanctioned by the University Grants Commission, New Delhi, for financial support of this work. This work was supported by the DGICYT of Spain (Projects CTQ2011-27512/BQU and CONSOLIDER INGENIO 2010 CSD2010-00065, FEDER funds) and the Direcció General de Recerca i Innovació del Govern Balear (Project 23/2011, FEDER funds). We thank the CTI (UIB) for allocation of computational time. P.B. thanks Gobierno de España MINECO (project CTQ2011-23014), Severo Ochoa Excellence Accreditation 2014-2018 (SEV-2013-0319) and the ICIQ Foundation for funding. We also thank Eduardo C. Escudero-Adán for XRay crystallographic data.

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CONCLUSIONS Five structurally equivalent M(II)−malonate (M = Ni, Co, Mn, Mg, Zn) complexes (1−5) have been determined by single crystal X-ray diffraction and the supramolecular self-assembly of these five complexes are found to be identical in nature. A discrete water dimer and the protonated 3-picoline play primarily role in mediating the self-assembly process of these complexes by means of hydrogen bonding interactions. In the resultant supramolecular organization other weaker forces like lone pair(anion)−π and π−π interactions are also important to stabilize 1D chain constructed by discrete [MII(C3H2O4)2(H2O)2] units. The copper complex presents a totally different solid state architecture because of the absence of coordinated water molecules. The computational study has been extended to both type of structures, highlighting the impact of the anion−π interactions in concert with π−π stacking in complexes 1−5 together with antiparallel CO--CO and hydrogen bonding interactions on the crystal packing phenomena. For the anion−π/π−π assembly, a mutual reinforcement of the two types of π−interactions has been demonstrated computationally. In compound 6, it is also remarkable the presence of an anion---π-hole interaction that has been rationalized by using the molecular electrostatic potential surface and NCI plot. Finally, the theoretical calculations enable the elucidation of the contributions of the different weak forces to molecular recognition by assigning discrete energy values to them. One of the most important aspects of the theoretical analysis reported herein is the elucidation of the contributions to molecular recognition and self-assembly by assigning discrete energy values to them. This provides helpful information to researchers working on supramolecular chemistry, crystal engineering or drug design to develop energy scoring functions.

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(1) Chisholm, J.; Pidcock, E.; Streek, J. V. D.; Infantes, L.; Motherwell, S.; Allen, F. H. Knowledge-Based Approaches to Crystal Design. CrystEngComm 2006, 8, 11−28. (2) Choudhury, S. R.; Jana, A. D.; Colacio, E.; Lee, H. M.; Mostafa, G.; Mukhopadhyay, S. Crowned Tetrameric Spirocyclic Water Chain: An Unusual Building Block of a Supramolecular Metal-Organic Host. Cryst. Growth Des. 2007, 7, 212−214. (3) Choudhury, S. R.; Jana, A. D.; Chen, C.−Y.; Dutta, A.; Colacio, E.; Lee, H. M.; Mostafa, G.; Mukhopadhyay, S. pH-triggered Changes in the Supramolecular Self-Assembly of Cu(II) Malonate Complexes. CrystEngComm 2008, 10, 1358−1363. (4) Choudhury, S. R.; Gamez, P.; Robertazzi, A.; Chen, C.-Y.; Lee, H. M.; Mukhopadhyay, S. Experimental Observation of Supramolecular Carbonyl-π/π-π/π-carbonyl and Carbonyl-π/π-π/π-Anion Assemblies Supported by Theoretical Studies. Cryst. Growth Des. 2008, 8, 3773− 3784. (5) Choudhury, S. R.; Lee, H. M.; Hsiao, T.-H.; Colacio, E.; Jana, A. D.; Mukhopadhyay, S. Co-operation of π···π, Cu(II)...π, Carbonyl···π and Hydrogen-Bonding Forces Leading to the Formation of Water Cluster Mimics Observed in The Reassessed Crystal Structure of [Cu(mal)(phen)(H2O)]23H2O (H2mal = malonic acid, phen = 1,10phenanthroline). J. Mol. Struct. 2010, 967, 131−139. (6) Das, A.; Dey, B.; Jana, A. D.; Hemming, J.; Helliwell, M.; Lee, H. M.; Hsiao, T.-H.; Suresh, E.; Colacio, E.; Choudhury, S. R.; Mukhopadhyay, S.; et al. Effect of Protonated Aminopyridines on the Structural Divergences of M(II)−Malonate Complexes (M = Cu, Ni, Co). Polyhedron 2010, 29, 1317−1325. (7) Das, A.; Choudhury, S. R.; Dey, B.; Yalamanchili, S. K.; Helliwell, M.; Gamez, P.; Mukhopadhyay, S.; Estarellas, C.; Frontera, A. Supramolecular Assembly of Mg(II) Complexes Directed by Associative Lone Pair-π/π-π/π-Anion-π/π-Lone Pair Interactions. J. Phys. Chem. B 2010, 114, 4998−5009. (8) Manna, P.; Seth, S. K.; Das, A.; Hemming, J.; Prendergast, R.; Helliwell, M.; Choudhury, S. R.; Frontera, A.; Mukhopadhyay, S. Anion Induced Formation of Supramolecular Associations Involving Lone Pair−π and Anion−π Interactions in Co(II) Malonate Complexes: Experimental Observations, Hirshfeld Surface Analyses and DFT Studies. Inorg. Chem. 2012, 51, 3557−3571 and references cited therein.. (9) Mitra, M.; Manna, P.; Seth, S. K.; Das, A.; Meredith, J.; Helliwell, M.; Bauzá, A.; Choudhury, S. R.; Frontera, A.; Mukhopadhyay, S.; et al. Salt-Bridge− π (sb−π) Interactions at Work: Associative Interactions of sb−π, π−π and Anion−π in Cu(II)-Malonate−2-

ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic data in CIF format for 1, 2, 3, 4, 5, and 6 (CCDC Nos. 1003677, 1003678, 1003679, 1003680, 1003675, and 1003676, respectively for 1, 2, 3, 4, 5, and 6) and fingerprint plots S1−S7 and Tables S1−S12 giving crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

* E-mail: [email protected] (S.R.C.). * E-mail: [email protected] (A.F.). * E-mail: [email protected] (S.M.). 14725



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Aminopyridine−Hexafluoridophosphate Ternary System. CrystEngComm 2013, 15, 686−696. (10) Seth, S. K.; Manna, P.; Singh, N. J.; Mitra, M.; Jana, A. D.; Das, A.; Choudhury, S. R.; Kar, T.; Mukhopadhyay, S.; Kim, K. S.; et al. Molecular Architecture Using Novel Types of Noncovalent πInteractions Involving Aromatic Neutrals, Aromatic Cations and πAnions. CrystEngComm 2013, 15, 1285−1288. (11) Mitra, M.; Seth, S. K.; Choudhury, S. R.; Manna, P.; Das, A.; Helliwell, M.; Bauzá, A.; Frontera, A.; Mukhopadhyay, S. M(II)− Malonate Complexes (M = Mg, Cu, Ni and Co) Characterized by Layered Structures: Experimental Observation, Hirshfeld Surface Analysis and Theoretical Study. Eur. J. Inorg. Chem. 2013, 4679−4685. (12) Mitra, M.; Manna, P.; Das, A.; Seth, S. K.; Helliwell, M.; Bauzá, A.; Choudhury, S. R.; Frontera, A.; Mukhopadhyay, S. On the Importance of Unprecedented Lone Pair−Salt Bridge Interactions in Cu(II)-Malonate−2-Amino-5-Chloropyridine−Perchlorate Ternary System. J. Phys. Chem. A 2013, 117, 5802−5811. (13) Murray, J. S.; Lane, P.; Clark, T.; Riley, K. E.; Politzer, P. σHoles, π-Holes and Electrostatically-Driven Interactions. J. Mol. Model. 2012, 18, 541−548. (14) Politzer, P.; Murray, J. S.; Clark, T. Halogen Bonding: An Electrostatically-Driven Highly Directional Noncovalent Interaction. Phys. Chem. Chem. Phys. 2010, 12, 7748−7757. (15) Solimannejad, M.; Ramezani, V.; Trujillo, C.; Alkorta, I.; Sánchez−Sanz, G.; Elguero, J. Competition and Interplay between σHole and π-Hole Interactions: A Computational Study of 1:1 and 1:2 Complexes of Nitryl Halides (O2NX) with Ammonia. J. Phys. Chem. A 2012, 116, 5199−5206. (16) Esrafili, M. D.; Mohammadian, S. F.; Solimannejad, M. A Theoretical Evidence for Mutual Influence Between S···N(C) and Hydrogen/Lithium/Halogen Bonds: Competition and Interplay Between p-Hole and r-Hole Interactions. Struct. Chem. 2014, 25, 1197−1205. (17) Ahlrichs, R.; Bär, M.; Hacer, M.; Horn, H.; Kömel, C. Electronic Structure Calculations on Workstation Computers: The Program System Turbomole. Chem. Phys. Lett. 1989, 162, 165−169. (18) Boys, S. B.; Bernardy, F. The Calculation of Small Molecular Interactions by the Differences of Separate Total Energies. Some Procedures With Reduced Errors. Mol. Phys. 1970, 19, 553−566. (19) Bader, R. F. W. A Quantum Theory of Molecular Structure and its Applications. Chem. Rev. 1991, 91, 893−928. (20) Keith, T. A. AIMAll (Version 13.05.06); TK Gristmill Software: Overland Park KS, 2013. (21) SADABS Bruker AXS; Bruker: Madison, WI, 2004. SAINT, Software Users Guide, Version 6.0; Bruker Analytical X-ray Systems: Madison, WI, 1999. Sheldrick, G. M. SADABS v2.03: Area-Detector Absorption Correction; University of Göttingen: Göttingen, Germany, 1999. Saint + Version 7.60A (Bruker AXS 2008); SADABS V. 2008−1 (2008). (22) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; Giacovazzo, C.; Mallamo, M.; Mazzone, A.; Polidori, G.; Spagna, R.; et al. SIR2011: A New Package for Crystal Structure Determination and Refinement. J. Appl. Crystallogr. 2012, 45, 357− 361. (23) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr. 2008, A64, 112−122. (24) Wan, C.-Q.; Mak, T. C. W. Unusual Carbonyl···Carbonyl Interaction in Supramolecular Structures of Silver(I) Complexes with 2,6-Pyridinediylbis(4-pyridinyl)methanone. Cryst. Growth Des. 2011, 11, 832−842. (25) Barceló-Oliver, M.; Baquero, B. A.; Bauzá, A.; García-Raso, A.; Terron, A.; Mata, I.; Molins, E.; Frontera, A. Experimental and Theoretical Study of Thymine and Cytosine Derivatives: The Crucial Role of Weak Noncovalent Interactions. CrystEngComm 2012, 14, 5777−5784. (26) Manikumari, S.; Shivaiah, V.; Das, S. K. Identification of a NearLinear Supramolecular Water Dimer, (H2O)2, in the Channel of an Inorganic Framework Material. Inorg. Chem. 2002, 41, 6953−6955 and references cited therein..

(27) Torii, H. Extended Nature of the Molecular Dipole of Hydrogen-Bonded Water. J. Phys. Chem. A 2013, 117, 2044−2051. (28) Fellers, R. S.; Leforestier, C.; Braly, L. B.; Brown, M. G.; Saykally, R. J. Spectroscopic Determination of the Water Pair Potential. Science 1999, 284, 945−948. (29) Janes, R.; Moore, E. A. In Metal-Ligand Bonding; Abel, E. W., Ed.; RSC Publishing: London, 2004. (30) Kamer, K. J.; Choudhary, A.; Raines, R. T. Intimate Interactions with Carbonyl Groups: Dipole−Dipole or n→π*? J. Org. Chem. 2013, 78, 2099−2103. (31) Singh, U. C.; Kollman, P. A. An Approach to Computing Electrostatic Charges for Molecules. J. Comput. Chem. 1984, 5, 129− 145. (32) Sigfridsson, E.; Ryde, U. Comparison of Methods for Deriving Atomic Charges from the Electrostatic Potential and Moments. J. Comput. Chem. 1998, 19, 377−395. (33) Johnson, E.; Keinan, S.; Mori-Sánchez, P.; Contreras-García, J.; Cohen, A.; Yang, W. Revealing Non-Covalent Interactions. J. Am. Chem. Soc. 2010, 132, 6498−6506. (34) Contreras-García, J.; Keinan, S.; Chaudret, R.; Piquemal, J.; Beratan, D.; Yang, W. NCIPLOT: A Program for Plotting NonCovalent Interaction Regions. J. Chem. Theory Comput. 2011, 7, 625− 632. (35) Contreras-García, J.; Yang, W.; Johnson, E. R. Analysis of Hydrogen-Bond Interaction Potentials from the Electron Density: Integration of Noncovalent Interaction Regions. J. Phys. Chem. A 2011, 115, 12983−12990. (36) Spackman, M. A.; McKinnon, J. J. Fingerprinting Intermolecular Interactions in Molecular Crystals. CrystEngComm 2002, 4, 378−392. (37) McKinnon, J. J.; Jayatilaka, D.; Spackman, M. A. Towards Quantitative Analysis of Intermolecular Interactions With Hirshfeld Surfaces. Chem. Commun. 2007, 3814−3816. (38) Spackman, M. A.; McKinnon, J. J.; Jayatilaka, D. Electrostatic Potentials Mapped on Hirshfeld Surfaces Provide Direct Insight into Intermolecular Interactions in Crystals. CrystEngComm 2008, 10, 377−388. (39) Seth, S. K.; Saha, I.; Estarellas, C.; Frontera, A.; Kar, T.; Mukhopadhyay, S. Supramolecular Self-Assembly of M-IDA Complexes Involving Lone-Pair···π Interactions: Crystal Structures, Hirshfeld Surface Analysis, and DFT Calculations [H2IDA = Iminodiacetic Acid, M = Cu(II), Ni(II)]. Cryst. Growth Des. 2011, 11, 3250−3265. (40) Seth, S. K. Tuning the Formation of MOFs by pH Influence: XRay Structural Variations and Hirshfeld Surface Analyses of 2-Amino5-nitropyridine With Cadmium Chloride. CrystEngComm 2013, 15, 1772−1781. (41) Spackman, M. A.; Byrom, P. G. A Novel Definition of a Molecule in a Crystal. Chem. Phys. Lett. 1997, 267, 215−220. (42) McKinnon, J. J.; Mitchell, A. S.; Spackman, M. A. Hirshfeld Surfaces: A New Tool for Visualising and Exploring Molecular Crystals. Chem.Eur. J. 1998, 4, 2136−2141. (43) Rohl, A. L.; Moret, M.; Kaminsky, W.; Claborn, K.; Mckinnon, J. J.; Kahr, B. Hirshfeld Surfaces Identify Inadequacies in Computations of Intermolecular Interactions in Crystals: Pentamorphic 1,8-Dihydroxyanthraquinone. Cryst. Growth Des. 2008, 8, 4517−4525. (44) Parkin, A.; Barr, G.; Dong, W.; Gilmore, C. J.; Jayatilaka, D.; Mckinnon, J. J.; Spackman, M. A.; Wilson, C. C. Comparing Entire Crystal Structures: Structural Genetic Fingerprinting. CrystEngComm 2007, 9, 648−652. (45) Wolff, S. K.; Grimwood, D. J.; McKinnon, J. J.; Jayatilaka, D.; Spackman, M. A. CrystalExplorer 2.1; University of Western Australia: Perth, Australia, 2007.

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Malonate Complexes - American Chemical Society

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