A Systematic Evaluation of the Interplay of Weak and Strong

Article pubs.acs.org/crystal

A Systematic Evaluation of the Interplay of Weak and Strong Supramolecular Interactions in a Series of Co(II) and Zn(II) Complexes Tuned by Ligand Modification Konstantina A. Kounavi,† Manolis J. Manos,‡ Eleni E. Moushi,‡ Alexandros A. Kitos,† Constantina Papatriantafyllopoulou,† Anastasios J. Tasiopoulos,‡ and Vassilios Nastopoulos*,† †

Department of Chemistry, University of Patras, 265 04 Patras, Greece Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus

‡

S Supporting Information *

ABSTRACT: A systematic investigation on a designed series of 21 transition metal complexes has been carried out with the intention to explore and assess the relative strength and the way in which intermolecular interactions, namely, weak and strong hydrogen-bonding and π−π interactions, cooperate and direct molecular association during crystallization. The complexes were prepared using the general MII/X−/L or HL′ (MII = CoII, ZnII; X− = Cl−, Br−, I−, NO3−, NO2−, ClO4−; L = 1-methyl-4,5-diphenylimidazole; and HL′ = 4,5-diphenylimidazole) reaction system and were characterized by single-crystal X-ray crystallography. Although the two ligands are structurally similar, the crystal packing organization of their complexes is markedly different. In structures with L, the 3D assembly is based only on weak C−H···X, C−H···π, and intramolecular π···π stacking interactions, whereas in those with HL′, it is the recurring N−H···X motifs that clearly dominate and guide the molecular self-assembly. The formation of such synthons has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. In parallel, the conformational flexibility of the two ligands serves a dual purpose: (i) L contributes to the stabilization of complexes via intramolecular π···π stacking interactions, and (ii) HL′ facilitates the synthon formation by adopting appropriate conformations, even at the expenses of the stabilizing intramolecular π···π stacking.

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INTRODUCTION It is well-known that the crystal packing principles, by which discrete molecules are mutually recognized and put together in periodic ordered arrays to reach an equilibrium structure, are based on various parameters such as molecular shape and symmetry, complementarity of molecular surfaces,1 as well as on the concerted action of weak intermolecular noncovalent interactions.2 In turn, through the understanding and control of these weak interactions, crystal engineering deals with the design, synthesis, and evaluation of solid-state supramolecular structures with tailored form and function,3 that is, from the designed chemistry of intermolecular forces to materials with, hopefully, desired properties. The construction of molecular assemblies through the coordination of a metal ion with organic ligands has attracted considerable attention and has evolved in an interesting research area of chemistry.4 The use of metals in supramolecular chemistry (termed metallosupramolecular) play essentially two, often complementary, roles: The first is that of purely structural components, and the second one is as a source of properties. Because of their interesting architectures and applications in diverse areas (e.g., optoelectronics, catalysis, magnetism, molecular recognition, etc.), a significant number of supramolecular metal complexes have been synthesized in the last several years.5 The two most commonly used approaches © 2011 American Chemical Society

for engineering the crystal structure of such complexes employ either coordinative bonds6 or hydrogen bonds. 7 Both approaches and their combinations have resulted in the construction of predesigned 2D or 3D supramolecular architectures. Hydrogen bonds have attracted considerable interest due to their relative strength, directionality, and ability to act synergically, thus providing a directing force for the organization of individual molecules into well-defined supramolecular assemblies. In parallel, π···π stacking interactions,8 a class of nondirectional forces, are often encountered in biological, chemical, and materials science systems; they control many self-assembly and molecular recognition phenomena, and their significance in the context of crystal engineering should not be overlooked. Initial interest on the role and importance of these weak interactions has mainly focused on purely organic systems; however, there have been a few previous reports on transition metal complexes. In this regard, it seemed interesting to conduct a systematic investigation on a designed series of transition metal complexes with the intention to understand and assess the relative strength Received: September 26, 2011 Revised: November 4, 2011 Published: December 21, 2011 429

dx.doi.org/10.1021/cg201271p | Cryst. Growth Des. 2012, 12, 429−444

Crystal Growth & Design

Article

chemistry. Specifically, (i) ZnII, and to a lesser extent CoII, are air-stable; therefore, it would not be necessary to carry out the synthetic work under inert conditions. (ii) Both metal ions are classified as intermediate according to the model of Hard and Soft Acids and Bases (HSAB); therefore, it was expected that their complexes with N, O, and other donors (e.g., Cl−, Br−) used would be stable. (iii) Both metal ions are located on the right of the Irving−Williams series, ensuring significant thermodynamic stability for their complexes, a key issue in crystal engineering. (iv) The electronic structures of the complexes of the two metal ions are different, and one would expect different tecton shapes, which could make our study more interesting and not limited to a single geometry. Thus, the small difference in the crystal field stabilization energy (CFSE) between octahedral and tetrahedral geometry in CoII [3d7] is expected to result in complexes with both geometries, whereas in the case of ZnII [3d10], the zero CFSE could lead, depending on the ligands, to a variety of stereochemistries. Three criteria were considered for the selection of the ions X− used: (i) Their tendency to act as terminal ligands, either monodentate or chelating, to avoid isolation of coordination polymers; (ii) their ability to coordinate (e.g., Cl−, Br−, I−, NO3−, NO2−) or act as counterions (e.g., ClO4−): neutral and cationic complexes were expected, respectively; both types are welcome to study the effect of charge on the supramolecular structures of the complexes; (iii) their size: In the case the anions would act as ligands, their size was expected to determine (for a given organic ligand) the stoichiometry of the complexes. We wanted to isolate different types of complexes for a given metal ion and organic ligand with the purpose to study the effect of the stoichiometry of the tectons in the formation of the supramolecular packing motifs. Regarding the methodology used, it comprises a variety of reactions of simple metal salts (MX2) with L and HL′ ligands, product isolation, crystallization, characterization by spectroscopic methods, and crystal structure determination by singlecrystal X-ray diffraction, followed by a detailed analysis of the supramolecular forces dominating the self-assembly of the complexes. The parameters studied include the nature of MII, X−, the ligand, the reaction solvent, the molar ratio of reagents, the crystallization solvent, and the crystallization method. The effect of the last two parameters could potentially lead to isolation of polymorphs. Polymorphism, although it adds complexity to a crystal engineering system, it provides on the other hand opportunities to study a specific chemical entity in different crystalline environments.18 In each group of experiments, we tried to vary only one parameter at a time, keeping most of the others constant, so as to isolate the maximum number of products for a given reaction system. We present here the results of this approach; 21 new coordination complexes have been obtained by implementing the MII/X−/(L or HL′) general reaction system presented above. Among them, 1a and 1b, as well as 11a and 11b, represent two groups of conformational polymorphs. The crystal structures of the free ligands L and HL′ have also been determined and included in this study to investigate the role of ligand conformation in the free and coordinated form. These complexes have proven to be useful starting materials for the entry to our supramolecular program.

and the way in which weak interactions cooperate and direct the supramolecular assembly of the molecular building blocks. From the dual role of metal ions, we were interested in their role as structural components, whereas from the palette of weak supramolecular forces, we focused our interest on hydrogen bonds and π···π stacking interactions, thereby excluding the study of the coordinative bond as a parameter of our efforts. It should be noted that the coordinative bond as supramolecular synthon9 has been studied extensively over the last 20 years (catenanes, rotaxanes, molecular knots, coordination polymers, metal−organic frameworks, etc.). The main advantage of using transition metal ions in crystal engineering is that the shape of the tecton can be regulated by specific metal−ligand systems with appropriate coordination geometry. Then, desired supramolecular synthons could result using certain ligand groups that cannot be coordinated and therefore can act on the supramolecular association of the tectons. Two substituted imidazoles, 1-methyl-4,5-diphenylimidazole (L) and 4,5-diphenylimidazole (HL′), were used as organic ligands in our efforts (Scheme 1). Imidazole and its derivatives Scheme 1. Neutral Monodentate Ligands L and HL′a

a

The ring numbering is denoted in circles.

have played a formative role in the development of coordination chemistry10,11 and are particularly interesting ligands in bioinorganic12,13 and metallosupramolecular9 chemistry. The presence of a donor atom (the pyridine type N3 atom) that can form a coordination bond and of a hydrogenbond donor (the pyrrolic type N1 atom), combined with the πexcessive character of the 5-membered heterocyclic ring, can lead to intermolecular assembly of metal complexes through ligand−ligand or ligand−inorganic anion interactions. The choice of the monodentate ligands L and HL′ was based on the following considerations: (i) They have similar molecular structures and therefore comparative studies are easier, (ii) both ligands have two phenyl rings that can form π···π interactions, and (iii) ligand L, in contrast to HL′, is unable to form a “classical” hydrogen bond because the N1 ring atom is connected to a −CH3 group. Thus, the determination of crystal structures of metal complexes of L and HL′ could provide important information for the comparative assessment of hydrogen bonding and π···π interactions in metallosupramolecular chemistry, especially if such a comparison took place for complexes of the same metal and the same inorganic anion with a similar structure. There is in fact relatively little known about the coordination chemistry of heavily substituted imidazoles and, in particular, about L14−16 and HL′.17 The metal ions (MII) used were CoII and ZnII, and their choice was based on known principles of their coordination

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RESULTS AND DISCUSSION Brief Synthetic Comments. Various reactions have been systematically explored with differing reagent ratios, reaction

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Scheme 2. Synthetic Routes for the CoII and ZnII Complexes Containing Ligands L and HL′

coordinated ions, and the counterions/solvents for all compounds presented herein. From the molecular point of view, the mean planes of the phenyl rings 2 and 3 of L are tilted by 29.8(1)° and 47.8(1)°, respectively, with regard to the imidazole plane (Table S1 in the Supporting Information). In the absence of groups capable of establishing strong hydrogen bonding, the molecules are associated by a mixture of weak intermolecular interactions, such as π···π, C−H···π (T-shaped), and C−H···N interactions, leading to a 3D packing (Figure 1). In the case of HL′, whose asymmetric unit contains two unique molecules A and B (Z′ = 2) with highly similar conformation (overlay rmsd: 0.059 Å), its packing organization alters decisively. The structure may be viewed as consisting of alternating slabs of A and B molecules parallel to the (1̅01) plane. A and B type molecules are linked to each other along the [101] direction by strong N−H···N bonds to form infinite −A−B− chains (Figure 2). The corresponding phenyl/ imidazole mean plane angles are −39.8(2)° and −33.8(2)° for molecule A and −35.5(2)° and −41.8(2)° for molecule B, indicating a significant conformational change compared with ligand L, presumably to reduce steric hindrance in the formation of the dominant N−H···N bonds. Inspection for other interactions shows that, unlike L, π···π interactions between the packed molecules are hampered, and only some very weak C−H···π contacts between phenyl rings of adjacent chains can be considered. It should be noted that the structure

solvents, hydro(solvo)thermal conditions, and other conditions to prepare the cobalt(II) and zinc(II) complexes of L and HL′ of this study (eq 1). In some cases, triethyl orthoformate (TEOF) was added as a drying agent. The general synthetic route as well as their individual formulas is illustrated in Scheme 2.

As expected, reactions with Co(ClO4)2·6H2O and Zn(ClO4)2·6H2O led to products with different stoichiometry (5, 10, 15, and 19) due to the weak coordinating capability of the perchlorate anion used. Compound 8, [CoI(HL′)3]I, an exception from the two general types of products (eq 1), has been isolated by conventional conditions; the anticipated [CoI 2 (HL) 2 ] compound has also been prepared (by solvothermal conditions) but is not included in the list because of its poor refinement indices. Crystal data and structure refinement parameters for all compounds are given in Tables 1 and 2. Description of the Structures of Ligands L and HL′. Note: To facilitate discussion, molecular comparison, and overlay, the same numbering scheme has been assigned (where applicable) to the ligand atoms and rings (Scheme 1), the 431



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Table 1. Crystal and Structure Refinement Parameters for the Co Compounds 1a−10 compd

1a

1b

2

3

4

formula

C32H28Cl2CoN4

C32H28Cl2CoN4

C32H28Br2CoN4

C32H28CoI2N4

C32H28CoN6O4

Mr (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z, Z′ dcalcd (g cm−3) radiation/μ (mm−1) reflns collected/ unique parameters/ restraints R1, wR2a goodness-of-fit on F2 Δρmax /Δρmin (e Å−3) compd

598.41 monoclinic P21/n 9.7672(5) 14.0066(7) 21.7244(10) 90 98.867(4) 90 2936.5(3) 4, 1 1.354 Mo Kα/0.794 24360/7030


687.33 tetragonal I41cd 28.6528(13) 28.6528(13) 14.0756(7) 90 90 90 11555.8(11) 16, 1 1.580 Mo Kα/3.389 35947/6960



C64H56CoN8·2(ClO4)· 1.26(CH3OH)·0.74(H2O) 1248.70 monoclinic C2/c 25.1956(7) 17.7799(5) 13.5452(4) 90 103.003(3) 90 5912.3(3) 4, 0.5 1.403 Mo Kα/0.449 25845/7799

354/12

354/0

354/1

354/1

390/1

413/11

0.0304, 0.0666 0.942

0.0281, 0.0661 0.981

0.0302, 0.0435 0.882

0.0297, 0.0686 1.053

0.0332, 0.0675 1.018

0.0474, 0.0974 0.942

0.47/−0.30

0.38/−0.38

0.53/−0.40

0.67/−0.59

0.30/−0.38

0.81/−0.51

formula Mr (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z, Z′ dcalcd (g cm−3) radiation/μ (mm−1) reflns collected/ unique parameters/ restraints R1, wR2a goodness-of-fit on F2 Δρmax /Δρmin (e Å−3) a

5

6

7

8

9

10

C30H24Cl2CoN4·2(CH2Cl2)·H2O 758.23 triclinic P1̅ 9.3142(7) 12.3652(8) 15.2440(7) 83.582(5) 88.587(5) 82.464(6) 1729.5(2) 2, 1 1.456 Mo Kα/0.992

C30H24Br2CoN4·CH2Cl2 744.21 monoclinic P21/n 16.3578(7) 9.8345(4) 19.5282(8) 90 104.983(4) 90 3034.7(2) 4, 1 1.629 Mo Kα/3.403

C45H36CoIN6·I 973.53 monoclinic I2/a 23.9011(8) 13.6947(5) 28.7631(12) 90 92.381(5) 90 9406.6(6) 8, 1 1.375 Mo Kα/1.712

C30H24CoN6O6 623.48 monoclinic P21/c 12.1557(4) 16.6468(5) 13.5929(4) 90 94.219(3) 90 2743.2(2) 4, 1 1.510 Cu Kα/5.392

C60H48CoN8·2(ClO4)·1.7(C3H6O)·H2O 1255.64 monoclinic P21/c 12.0949(3) 24.0933(5) 22.5656(6) 90 91.383(2) 90 6573.8(3) 4, 1 1.269 Mo Kα/0.405

12702/7179

17594/6274

9197/9197

4217/4217

14253/14253

409/6

367/2

505/135

395/50

815/36

0.0452, 0.0914 0.943

0.0282, 0.0494 0.903

0.0356, 0.0931 0.996

0.0558, 0.1479 1.065

0.0508, 0.1536 1.047

0.58/−0.55

0.54/−045

0.92/−0.59

0.80/−0.70

1.76/−0.92

R1 for I > 2σ(I), wR2 for all data.

of HL′ has been reported previously at 296 K in two polymorphic forms. The first polymorph19 [(I), P21/c, Z′ = 1, obtained by recrystallization from 2-propanol] shows significantly different phenyl/imidazole mean plane angles and packs differently; nevertheless, adjacent molecules retain the same N−H···N hydrogen bonding to form infinite chains along the b direction. The second one20 [(II), P21/n, Z′ = 2, obtained by recrystallizing polymorph (I) from acetonitrile] is the same with the structure reported herein at 100 K. Regardless of Z′, the dominance of the N−H···N motif is the main packing feature of HL′, whereas the role of π interactions

is cooperative since their directional preferences are satisfied within the geometrical constraints imposed by the strong motifs. In this aspect, the polymorph with Z′ = 2 could be seen as an attempt to optimize close crystal packing so as to increase favorable overlap of the aromatic rings. On the other hand, when the group that establishes the strong interactions is absent (ligand L), the action of the weak π interactions is more pronounced leading to an effective 3D pattern. Description of the Structures of Complexes with Ligand L. [MX2L2] Type Complexes. This group comprises complexes 1a, 1b, 2, and 3 and 11a, 11b, 12, and 13 [M = Co, 432



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Table 2. Crystal and Structure Refinement Parameters for the Zn Compounds 11a−19 and Ligands L and HL′ compd

11a

11b

12

13

14

15

formula Mr (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z, Z′ dcalcd (g cm−3) radiation/μ (mm−1) reflns collected/unique parameters/restraints R1, wR2a goodness-of-fit on F2 Δρmax /Δρmin (e Å−3) compd

C32H28Cl2N4Zn 604.85 monoclinic P21/n 9.7848(3) 14.0339(4) 21.6551(7) 90 98.583(3) 90 2940.4(2) 4, 1 1.366 Mo Kα/1.045 24573/7418 354/0 0.0282, 0.0744 1.054 0.39/−0.34 16

C32H28Cl2N4Zn 604.85 monoclinic P21/n 9.6576(2) 12.3700(2) 24.7293(3) 90 91.985(2) 90 2952.5(1) 4, 1 1.361 Mo Kα/1.040 24974/7439 354/0 0.0279, 0.0758 1.013 0.41/−0.30 17

C32H28Br2N4Zn 693.77 tetragonal I41cd 28.6569(4) 28.6569(4) 14.1002(2) 90 90 90 11579.3(3) 16, 1 1.592 Mo Kα/3.637 46446/4719 354/1 0.0336, 0.0710 0.985 1.06/−0.53 18

C32H28I2N4Zn 787.75 tetragonal I41cd 29.0876(3) 29.0876(3) 14.2312(3) 90 90 90 12040.9(4) 16, 1 1.738 Mo Kα/2.895 15756/5426 354/1 0.0239, 0.0548 1.018 0.40/−0.36

C32H28N6O4Zn 625.97 tetragonal I41cd 28.4382(5) 28.4382(5) 14.2749(4) 90 90 90 11544.6(4) 16, 1 1.441 Mo Kα/0.900 46183/6822 408/43 0.0350, 0.0875 1.070 0.93/−0.76

C64H56N8Zn· 2(ClO4)·C3H6O 1259.97 triclinic P1̅ 13.6132(3) 21.9563(4) 22.3675(4) 67.168(2) 89.266(2) 75.966(2) 5953.0(2) 4, 2 1.405 Mo Kα/0.569 90428/24553 1579/4 0.0405, 0.0560 0.810 0.78/−0.80 L HL′

formula Mr (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z, Z′ dcalcd (g cm−3) radiation/μ (mm−1) reflns collected/ unique parameters/ restraints R1, wR2a goodness-of-fit on F2 Δρmax /Δρmin (e Å−3) a

C30H24Cl2N4Zn· H2O 594.84 triclinic P1̅ 12.4444(5) 14.5245(5) 16.6375(5) 73.575(3) 86.395(3) 79.006(3) 2831.4(2) 4, 2 1.395 Mo Kα/1.086 26388/11727

C30H24Br2N4Zn· CH2Cl2 750.65 monoclinic P21/n 16.3250(8) 9.8402(6) 19.4897(10) 90 105.113(5) 90 3022.6(3) 4, 1 1.650 Mo Kα/3.661 13554/5895

709/13

C30H24N6O6Zn

19

C16H14N2

C15H12N2

629.92 monoclinic P21/c 12.1497(11) 16.6547(17) 13.6381(13) 90 94.134(9) 90 2752.5(5) 4, 1 1.520 Mo Kα/0.949 4827/4827

C60H48N8Zn· 2(ClO4)·2(C2H6O)· 2(CHCl3)·H2O 1494.22 monoclinic P21/c 12.7797(3) 12.0442(3) 44.9891(11) 90 91.257(2) 90 6923.1(3) 4, 1 1.434 Cu Kα/3.866 28761/13148

234.29 monoclinic P21/c 11.4635(2) 8.9100(2) 12.0381(2) 90 93.784(2) 90 1226.9(1) 4, 1 1.27 Mo Kα/0.076 10351/3166


367/2

395/4

873/8

164/0

313/2

0.0387, 0.1015

0.0369, 0.0646

0.0772, 0.1928

0.0665, 0.1685

0.981

0.902

1.066

1.075

0.0363, 0.0968 1.082

0.0359, 0.0983 1.055

0.96/−0.51

1.09/−0.94

1.49/−0.98

1.11/−1.07

0.31/−0.19

0.20/−0.23

R1 for I > 2σ(I), wR2 for all data.

the exception of polymorphs 1b and 11b, each complex is stabilized by two intramolecular π···π stacking interactions between aromatic rings of the two ligands: A1/B2 and B1/A2 (Table S2 in the Supporting Information). It seems that steric effects and the distorted tetrahedral geometry of the CoII and ZnII centers facilitate those interactions, providing rigidity within the complex. Similar π···π interactions have also been evidenced in a previously characterized Pd(II) complex15 and in a series of analogous complexes16 of other divalent metals with L, as well as in Cu(II) and Zn(II) complexes of 2-[2′-(4′,6′-ditert-butylhydroxyphenyl)]-4,5-diphenylimidazole.21,22 This information records a characteristic structural pattern of the complexes bearing the 4,5-diphenylimidazole moiety and supports the suitability of ligand L as a crystal engineering tool. The molecular structure of 1a is shown in Figure 3; an

Zn; X = Cl, Br, I) (Scheme 2). The X-ray analysis reveals two pairs of polymorphs: 1a−1b and 11a−11b. Furthermore, 1a− 11a, 2−12, and 3−13 are pairs of isomorphous compounds since (i) both structures of each pair have the same space group and quite similar cell dimensions and (ii) the types and the positions of atoms in both structures are the same except for a replacement of the Co atom with a Zn atom. Therefore, description will be presented mostly for one complex of each pair (Figure S1 in the Supporting Information). In all eight neutral complexes, the metal center has a distorted tetrahedral N2X2 coordination involving one pyridine type nitrogen donor atom from each ligand L and the two terminal halogen atoms. The two ligands (A and B) are mutually arranged in a syn fashion and in an “antiparallel” way with their methyl groups pointing at opposite directions. With 433



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Variation in the crystallization method yielded polymorphs 1a (reflux conditions) and 1b (solvothermal conditions). The two structures differ in conformation, notably in the coordination angle N3A−Co−N3B [105.5(1)° for 1a and 116.2(1)° for 1b] and the orientation of the phenyl rings of each ligand relative to the imidazole ring (Table S1 in the Supporting Information). The increase of the N3A−Co−N3B angle brings the two ligands of 1b at a greater distance (as compared to those of 1a), discouraging the formation of the intramolecular π···π motif and leading to an “unfolding” of the complex (Figure S2 in the Supporting Information). These conformational differences affect the supramolecular assembly of the structures: The molecules in 1a are packed into a 3D network via intermolecular C−H···Cl and C−H···π interactions, while 1b has a less efficient packing in which molecules are only connected to each other in layers parallel to the (101) plane via C−H···Cl interactions (Table 4). Each of the bromo- (2) and iodo- (3) analogous complexes has a similar molecular conformation to that of the chlorocontaining complex 1a. It is worth pointing out that in all three structures the halogeno ions act as multihydrogen-bonded acceptors. Depending on their atomic radii, this amounts to two C−H···Cl intramolecular bonds for structure 1, up to four C− H···Br bonds for 2, and up to five C−H···I bonds for 3. Overall, the intramolecular π···π stacking pattern in 1a, 2, and 3 contributes to the rigidity of the discrete complexes, while the extensive network of intermolecular C−H···X (X = Cl, Br, I) interactions play a crucial role in the formation and further stabilization of their 3D architectures (Figure 4). The importance of the combined, cooperative effect of those weak interactions to the final cohesion of the structures is manifested in polymorph 1b, where failure of the structure to establish the intramolecular π···π motif results in a 2D assembly. Substitution of Co(II) in 1a, 1b, 2, and 3 with Zn(II) does not alter the distorted tetrahedral coordination geometry of the resultant complexes 11a, 11b, 12, and 13, respectively, giving rise to isomorphous compounds with same packing organization relative to their Co(II) counterparts (Figure S1 and Table S3 in the Supporting Information). [M(NO2)2L2] Type Complexes 4 and 14. By substituting in the reaction system the monodentate halogeno ions with the nitrite anion, capable of acting as monodentate or bidentate chelating ligand, the structures of the isomorphous compounds 4 [Co(II)] and 14 [Zn(II)] were obtained. The metal cation of the complexes is in a highly distorted octahedral environment, comprising the two imidazole nitrogen donor atoms and the four nitrite oxygen atoms (Figure 5). The ligands are mutually cis. Assuming the criteria suggested by Reedijk and coworkers23 concerning the nitrate coordination modes (monodentate, anisobidentate, and bidentate), the two nitrite ions of 4 are bidentate. In complex 14, one of its nitrites is bidentate, while the second one is classified as anisobidentate. However, the latter ion is disordered over two orientations (70:30 domain ratio), and the conclusion drawn above is based solely on the major component. The severe distortion of the octahedron originates from the acute N−Co(Zn)−N bite angle of the two chelating nitrite ligands [56.9(1)° and 57.4(1)° for 4 and 46.0(1)° and 55.4(1)° for 14]. In another view, the sixcoordinate Co(II) and Zn(II) centers could be regarded as having a distorted quasi-tetrahedral coordination with bonds directed toward the nitrogen atom of the bidentate nitrite groups instead of toward its oxygen atoms; however, this approach in not without criticism.24 As mentioned, with the

Figure 1. Weak intermolecular interactions observed in ligand L. Red dashed lines, imidazole rings π···π interactions [Cg···Cgi = 3.555(2) Å]; blue dashed lines, phenyl rings T-shaped interactions [C9−H9···Cgii = 3.773(2) Å]; green dashed lines, C6−H6A···N3iii = 3.614(2) Å. Most of the hydrogen atoms have been omitted for clarity. Symmetry codes: (i) 1 − x, −y, −z; (ii) x, −1/2 − y, −1/2 + z; (iii) 1 − x, 1/2 + y, −1/ 2 − z.

Figure 2. Unique molecules A and B (colored differently) of HL′ are linked to each other by N−H···N bonds to form infinite −A−B− chains. Hydrogen bonding is indicated by red dashed lines: N1A−H1A = 0.87(1) Å, N1A···N3B = 2.886(2) Å, and N1A−H1A···N3B = 164(1)° and N1B−H1B = 0.86(1) Å, N1B···N3A = 2.850(2) Å, and N1B−H1B···N3A = 179(1)°.

overview of the interactions observed in all crystal structures is given in Table 3.

Figure 3. Complex 1a showing the two pairs of intramolecular π···π stacking interactions (colored light blue and pink). Hydrogen atoms have been omitted. 434



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Table 3. Summary of the Various Strong and Weak Intra/Intermolecular Interactions Observed in the Crystal Structures of the Studied Compounds compd 1a

intra π···π

inter π···π

weak H-boncls

2

C−H···Cl C−H···π C−H···Cl C−H···π C−H···Br C−H···π C−H···I C−H···π C−H···O C−H···N C−H···π C−H···O C−H···CI

1b 2

2

3

2

4

2

5·1.26MeOH·0.74H2O 6·2CH2Cl2· ·H2O

4 1

7·CH2Cl2

1

8 9 10·1.7Me2CO·H2O

2

11a

2

11b 12

2

13

2

14

2

15·2Me2CO 16·2H2O

3 1

17·CH2C12

1

18 19·2EtOH·2CHCl3·H2O

1

C−H···Br C−H···Cl C−H···I C−H···O C−H···O

2 2

1

C−H···Cl C−H···π C−H···Cl C−H···Br C−H··· π C−H···I C−H···π C−H···O C−H···N C−H···π C−H···O C−H···C1 C−H···π C−H···Br C−H···Cl C−H···O C−H···O C−H···π

2

strong H-bonds

network 3D 2D 3D 3D 3D

O−H···O N−H···Cl N−H···O O−H···Cl N−H···Br

3D 3D

N−H···I N−H···O N−H···O O−H···O

3D 3D 3D

3D

3D 2D 3D 3D 3D

N−H···Cl N−H···O O−H···Cl N−H···Br N−H···O N−H···O O−H···O

3D 3D

3D 3D 3D

modeled as 63% MeOH and 37% H2O. The other half of the asymmetric unit is generated by a 2-fold axis passing through the Co(II) atom. As is shown in Figure 6, the metal is coordinated through the pyridine type nitrogen donor atom from each of the four L ligands resulting in a distorted tetrahedral geometry. The four ligands of the complex form two pairs related by the symmetry axis. Within each pair, the two ligands are arranged in a syn fashion to each other as in the previous structures, forming the same stabilizing intramolecular π···π stacking motif. Despite the abundance of aromatic rings in the crystal structure, no significant intermolecular π···π or C− H···π interactions have been detected, due to the separating action of the perchlorate ions. Instead, these latter uncoordinated ions play the major role in the supramolecular 3D organization of the structure. Through their oxygen atoms acting as multihydrogen-bonded acceptors, the perchlorates link neighboring [CoL4]2+ units of the structure by means of C−H···O bonds (Figure 7). The perchlorates and the

exception of the disordered nitrite ligand of 14, structures 4 and 14 are isomorphous with a molecular overlay rmsd of 0.093 Å. The compounds also possess the structural motif of intramolecular π···π stacking and, in a manner similar to that in the previous complexes, pack in 3D by means of weak intermolecular C−H···O and C−H···N interactions mediated by the nitrite groups as well as C−H···π interactions. [ML4](ClO4)2·Solvent Type Complexes 5 and 15. It has long been established that perchlorates are anions of low coordination ability. In this perspective, we decided to include the perchlorates in our studies aiming at possible interesting changes in the structure of the products. Indeed, the X-ray analysis of the crystals produced showed that perchlorates do not coordinate to the metals but instead act as counterions leading to charged cationic complexes with different stoichiometries than those discussed so far. In particular, the asymmetric unit of 5 consists of half a [CoL4]2+, one ClO4− counterion and a mixed solvent site, close to perchlorate, 435



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Table 4. Hydrogen-Bonding Geometry (Å, °) for 1a, 1b, 2, and 3a D−H···A

D−H

H···A

D···A

∠(DHA)

2.95 2.88 2.90 2.89

3.764(2) 3.772(2) 3.613(2) 3.747(2)

143 155 134 155

2.94 2.62 2.82

3.859(2) 3.494(2) 3.520(2)

161 157 133

3.03 2.88 3.11 3.11 3.13 2.98 2.67 2.71

3.962(3) 3.817(3) 3.930(3) 3.883(3) 4.051(3) 3.732(3) 3.492(3) 3.456(3)

164 164 149 142 169 139 147 138

3.15 3.13 3.15 3.32 3.10 3.28 3.27 2.67 2.70

4.053(5) 4.060(4) 3.995(5) 4.097(4) 3.867(5) 4.176(5) 4.076(5) 3.472(3) 3.543(5)

158 164 150 143 141 163 146 144 146

1a C6A−H6A1···Cl1i C6B−H6B3···Cl2ii C10A−H10A···Cl2iii C15B−H15B···Cgiv

0.96 0.96 0.93 0.93

C6A−H6A1···Cl2v C18A−H18A···Cl2v C10A−H10A···Cl1ii

0.96 0.93 0.93

C6A−H6A3···Br1vi C6B−H6B3···Br2vii C2A−H2A···Br1vi C2B−H2B···Br2vii C17A−H17A···Br1viii C17B−H17B···Br1ix C11A−H11A···Cgx C11B−H11B···Cgxi

0.96 0.96 0.93 0.93 0.93 0.93 0.93 0.93

1b

2

Figure 5. Molecular structure of 4. The two pairs of intramolecular π···π stacking interactions are colored light blue and pink. Hydrogen atoms have been omitted.

3 C6A−H6A3···I1vii C6B−H6B3···I2vi C2A−H2A···I1vii C2B−H2B···I2vi C17B−H17B···I1xii C17A−H17A···I1xiii C15A−H15A···I1xiv C11A−H11A··Cgxv C6B−H6B2···Cgxiii

0.96 0.96 0.93 0.93 0.93 0.93 0.93 0.93 0.96

disordered water molecules of the crystal structure are linked through O−H···O bonds in discrete clusters without further substantial interference in the assembly of the structure. The asymmetric unit of 15 contains two independent cations [ZnL4]2+ A and B, four ClO4− counterions, and two acetone solvent sites. The best fit between A and B is achieved by inverting one of them prior to molecular overlay, indicating that A and B form an approximately enantiomeric pair (Figure S3 in the Supporting Information). The conformation of A and that of the inverted B are roughly similar except, possibly due to steric requirements, for two localized areas in which the orientation of the involved phenyl rings of the two complexes is significantly different, thus precluding any symmetry relation between A and B. The coordination geometry about the Zn(II) center in both A and B is distorted tetrahedral as in the structure of 5. Nevertheless, the characteristic intramolecular π···π motif observed in 5 is now disrupted: There are two such

a Symmetry codes: (i) 1/2 − x, −1/2 + y, 1/2 − z; (ii) 1 − x, −y, −z; (iii) 1 + x, y, z; (iv) 1 − x, 1 − y, −z; (v) 1/2 − x, 1/2 + y, 1/2 − z; (vi) x, 1 − y, −1/2 + z; (vii) x, 1 − y, 1/2 + z; (viii) 1/2 + y, 1 − x, −1/4 + z; (ix) y, −1/2 + x, −1/4 + z; (x) 1 − x, y, −1/2 + z; (xi) 1 − y, −1/2 + x, 1/4 + z; (xii) 1 − y, 1/2 − x, −1/4 + z; (xiii) 1 − y, 1/2 + x, 1/4 + z; (xiv) −x, 1 − y, z; (xv) −x, y, 1/2 + z. Centroids: Cgiv (C7B to C12B), Cgx (C13A to C18A), Cgxi and Cgxv (N1B to C5B), and Cgxiii (C13B to C18B).

Figure 4. View of the crystal packing of complex 1a. Hydrogen atoms have been omitted. 436



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its strength and directionality on the self-assembly of the complexes. [MX2(HL′)2]·Solvent Type Complexes. This group includes complexes 6, 7, and 8 as well as 16 and 17 [M = Co, Zn; X = Cl, Br, I) (Scheme 2). Compounds 6 and 7, as their analogues 1a and 2, respectively, have a distorted tetrahedral N2X2 coordination and similar molecular conformations (Figure S4 in the Supporting Information), and their ligands are accommodated in a syn fashion to each other. Complex 8, a rather unexpected product in terms of stoichiometry, has a distorted tetrahedral N3X coordination. Repeated attempts to crystallize [CoI2(HL′)2], the analogue of 3, yielded compound 8 and weakly diffracting crystals of complex [CoI2(HL′)2]2·2H2O; the latter is not, however, included in this study because of the poor quality of X-ray analysis. At the first level of organization, the molecules of 6 are linked to each other via strong N−H···Cl and water-mediated N− H···O and O−H···Cl hydrogen bonding into a 2D layer structure, parallel to the (001) plane (Table 5). As shown in Figure 8, the resulting centrosymmetric rings are described by the R24(8), R22(12), and R44(16) graph-set motifs.25 At the second level of assembly, the CH2Cl2 molecules located among the layers connect them via weak C−H···Cl bonds into a 3D network (Figure 9). In an analogous way, molecules of 7 are linked to layers by strong N−H···Br bonds parallel to (101)̅ plane forming dimers with an R22(12) motif. Then, the CH2Cl2 molecules located among the layers connect them via weak C−H···Cl bonds into a 3D network. The organization of [CoI2(HL′)2]2·2H2O is the same as in compound 6, a result of the action of strong N−H···I and water-mediated N−H···O hydrogen bonding, described by the same graph-set motifs as well. In the absence of solvent molecules, the layers are further connected in 3D via weak intermolecular C−H···π bonds. The [CoI(HL′)3]+ cations of compound 8 (Figure S5 in the Supporting Information) are assembled in layers parallel to (001) plane via strong N−H···Icounterion and weak C− H···Icoordinated bonds forming a R24(20) motif. The 3D

Figure 6. [CoL4]2+ cation of compound 5. The perchlorate counterions and the disordered MeOH and H2O solvent molecules of the structure are not shown. The intramolecular π···π centroid distance is 3.681(1) Å for the two pairs of rings colored pale blue and 3.549(1) Å for those colored pink. Hydrogen atoms have been omitted.

interactions in complex A and only one in B. Interestingly, albeit the structures of 5 and 15 differ in terms of Z′ (0.5 and 2, respectively), molecular conformation, and type of solvents, the molecular assembly in 15 is, similarly to 5, directed by the perchlorate counterions distributed among the bulk of the [ZnL4]2+ complexes. No intermolecular π···π interactions have been detected, and a couple of weak C−H···π interactions observed are not deemed to have any significant role. The incorporated acetone molecule is simply held in the lattice via C−H···O bonds to a neighboring perchlorate and a [ZnL4]2+ unit without any structural implication. Description of the Structures of Complexes with Ligand HL′. In the absence of strong intermolecular bonds, the complexes discussed so far are assembled solely by weak intermolecular interactions. In the second series of complexes with HL′, the N1−CH3 group in ligand L has been deliberately changed with the N1−H donor group to exploit the impact of

Figure 7. Slab of the 3D structure of 5 showing the self-assembly of the [CoL4]2+ units mediated by the oxygen atoms of the perchlorate counterions acting as multihydrogen-bonded acceptors. The disordered MeOH and H2O solvents as well as hydrogen atoms have been omitted. 437



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Table 5. Hydrogen-Bonding Geometry (Å, °) for 6, 7, and 8a D−H···A

D−H

H···A

D···A

∠(DHA)

2.35(2) 1.85(2) 2.51(3) 2.38(3) 2.67 2.90

3.198(3) 2.715(4) 3.347(3) 3.205(3) 3.555(3) 3.775(3)

167(2) 171(3) 167(2) 162(3) 152 157

2.64(2) 2.73(2) 2.86 2.87 3.05

3.459(2) 3.570(2) 3.643(3) 3.593(2) 3.799(2)

165(2) 171(2) 142 136 138

2.79(4) 2.81(3) 2.85(4) 3.14

3.551(3) 3.644(3) 3.567(4) 4.041(4)

152(4) 164(4) 143(3) 165

6 N1A−H1A···Cl1i N1B−H1B···O1ii O1−H1···Cl2iii O1−H2···Cl2iv C19A−H19A···Cl1iii C11B−H11B···Cl4v

0.86(2) 0.87(2) 0.86(3) 0.86(3) 0.97 0.93

N1A−H1A···Br1vi N1B−H1B···Br1vii C2B−H2B···Br2vii C11A−H11A···Cl1viii C16B−H16B···Cl2ix

0.85(2) 0.85(2) 0.93 0.93 0.93

N1A−H1A···I2Ax N1B−H1B···I2Axi N1C−H1C···I2Axii C10B−H10B···I1xiii

0.84(4) 0.86(3) 0.85(3) 0.93

7

8

Figure 9. Three-dimensional structure of 6. The layers of the structure parallel to the ab plane are connected to a 3D network by the intervening dichloromethane solvent molecules (red dashed lines). The noncontact hydrogen atoms have been omitted.

Symmetry codes: (i) 2 − x, 1 − y, 2 − z; (ii) x, 1 + y, z; (iii) 1 − x, 1 − y, 2 − z; (iv) −1 + x, −1 + y, z; (v) 1 − x, 1 − y, 1 − z; (vi) 2 − x, 1 − y, 1 − z; (vii) 5/2 − x, −1/2 + y, 3/2 − z; (viii) x, −1 + y, z; (ix) 3/ 2 − x, −3/2 + y, 3/2 − z; (x) x, y, z; (xi) −1/2 + x, 1 − y, z; (xii) 1 − x, 1/2 + y, 3/2 − z; (xiii) 1 − x, −1/2 + y, 3/2 − z. a

As shown in Tables 4 and S4 in the Supporting Information, the number of intramolecular π···π interactions in compounds 6, 7, 8 (with three coordinated ligands), 16, and 17 with HL′ are markedly fewer as compared to their analogues 1a, 2, 3, 11a, 12, and 13 with L. This “unfolding” of the complexes, similar to that observed in the polymorphic pairs 1a/1b and 11a/11b, results from a significant increase of the N3A−Co− N3B coordination angle (ca. 110−119° for the first group and 97−106° for the second one) and might be attributed to a kind of “stretching” of the complexes exerted in the course of formation of the dominant hydrogen-bonding motifs described above. To summarize, it is evident from complexes 6, 7, 8, [CoI2(HL′)2]2·2H2O, 16, and 17 that the self-assembly of their supramolecular architectures is clearly guided by specific recurring hydrogen-bonding motifs N−H···X (X = Cl, Br, I, O), usually termed supramolecular synthons. These dominating synthons develop between imidazole N−H groups and halogen ions (coordinated or counterions) and/or solvent water molecules (depending on the composition of each structure). At the same time, the interaction of the N−H group with potentially strong acceptors to form supramolecular synthons favors the incorporation of solvent molecules such as H2O and CH2Cl2 in the crystal lattice. By contrast, the crystal structures of the analogous complexes isolated with L (1a, 1b, 2, 3, 11a, 11b, 12, and 13) do not retain any solvent because they lack strong hydrogen-bond donors capable of guiding molecules with electronegative atoms to settle around them. [M(NO3)2(HL′)2] Type Complexes 9 and 18. Compound [Co(NO3)2(HL′)2] (9) presents an interesting case, in terms of molecular conformation and subsequent supramolecular assembly, as compared to [Co(NO2)2L2] (4) and [Co(NO3)2L2]16a complexes. The cobalt ion is in a highly distorted octahedral N2O4 environment, comprising the two imidazole nitrogen atoms and four nitrate oxygen atoms (the coordination mode of the two nitrates being classified as anisobidentate). Unlike all complexes discussed so far, the two ligands of 9 are arranged anti to each other with their N1−H groups almost parallel and pointing to the same direction

Figure 8. Part of the structure of 6 showing the layer formed by strong N−H···Cl and N−H···O hydrogen-bonding parallel to the ab plane. The resulting ring patterns described by the R24(8), R22(12), and R44(16) motifs are shown in gray. The incorporated dichloromethane molecules and noncontact hydrogen atoms have been omitted.

construction is then completed via weak intermolecular π···π interactions. Regarding the zinc complexes 16 and 17, the asymmetric unit of 16, unlike its cobalt analogue 6, consists of two independent molecules (A and B) forming an approximately enantiomeric pair. Interestingly, despite these differences, the 2D molecular assembly is directed by the same hydrogenbonding pattern as in compound 6. Because of the lack of further solvent molecules, weak intermolecular C−H···π bonds have undertaken to complete the 3D structure. On the other hand, the zinc complex 17 is isomorphous to the cobalt complex 7. Repeated attempts to crystallize the iodo compound [ZnI2(HL′)2] did not yield any diffraction-quality crystals. 438



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surrounding [Co(HL′)4]2+ units via N−H···O synthons to settle around them in a fixed and repetitive manner, despite the competitive effects of other weaker and less specific interactions such as intra/intermolecular π···π interactions. Alternatively, the perchlorate anion can be described as a template that controls the self-assembly process and is a permanent part of the product.26 Indeed, there is only one intramolecular π···π interaction in structure 10 confirming the dominating role of the synthon, while in structure 5 it appears that a balance exists between weak π···π and C−H···Operchlorate interactions, allowing thus the formation of four intramolecular π···π interactions. The [Co(HL′)4]2+ units connect, via three of their N−H groups, to the ClO4− and H2O molecules forming N−H···O synthons, while the fourth N−H group forms a hydrogen bond to the Me2CO molecule. This results in chains of alternating [Co(HL′)4]2+ and ClO4−/H2O species running parallel to the 2fold screw axes (Figure 11). Weak C−H···O interactions strengthen further the individual chains and link them together creating a 3D structure. The conformation of the [Zn(HL′)4]2+ cation in compound 19 is roughly similar to that of compound 10 (Figure S6 in the Supporting Information). Although the two complexes crystallize with different kind and amount of solvent molecules, the assembly of the [Zn(HL′)4]2+ cations is also based upon N−H···O synthons, resulting in supramolecular layers composed of alternating [Zn(HL′)4]2+, ClO4−/H2O/EtOH, and ClO4−/EtOH/CHCl3 tapes parallel to the (204̅) plane (Figure 12). Weak C−H···O interactions contribute to the rigidity of the layers, and the 3D pattern is completed via weak C−H···O and C−H···π interactions interconnecting the layers.

(Figure 10). The same applies to the nitrate ions, allowing their uncoordinated O3 and O6 atoms to acquire complementary

Figure 10. Part of the 1D chain formed by N−H···O recurring motifs in the crystal structure of 9. Only contact hydrogen atoms are shown.

geometry with respect to the N1−H groups. These tectons are recognized by neighboring complexes to form pairs of supramolecular N−H···O synthons, resulting in well-formed 1D chains. This finding, in line with the fact that the zinc analogue 18 follows the same mode of packing (complex 18 is isomorphous to 9), suggests that the effect of the synthon to the molecular conformation adopted by 9 may be important. In its turn, the trans conformation favors the formation of intermolecular π···π stacking (Table 3), which, together with weak C−H···O interactions, contribute to the 3D expansion of the structure. [M(HL′)4](ClO4)2·Solvent Type Complexes 10 and 19. As in the analogous complex 5 with L, the structure of 10 consists of [Co(HL′)4]2+ cations in a distorted tetrahedral geometry, ClO4− counterions, as well as Me2CO and H2O solvent molecules (Figure 11). In the presence of N−H groups, the uncoordinated perchlorate ions act as tectons and guide the

■

CONCLUSIONS The study of a large sample of CoII and ZnII crystal structures allowed us to disclose the cooperative and competitive role of the intermolecular interactions responsible for determining the final supramolecular structures. The selection of L and HL′ as ligands introduced the basis (i) for different hydrogen-bonding possibilities, including both classical (N−H···O) and weak (C− H···Cl/Br/I/O), and (ii) for the formation of weak π-system interactions, viz. π···π and C−H···π. The introduction of appropriate ions X− (X− = Cl−, Br−, I−, NO3−, NO2−, ClO4−), coordinated or counterions, provided the necessary acceptor

Figure 11. Chain in the crystal structure of 10 formed by alternating [Co(HL′)4]2+ and ClO4−/H2O species running parallel to the 2-fold screw axes along b. Only contact hydrogen atoms are shown. 439



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Figure 12. Supramolecular layer generated by [Zn(HL′)4]2+, ClO4−/H2O/EtOH, and ClO4−/EtOH/CHCl3 tapes connected by N−H···O synthons and water-assisted O−H···O bonding in the structure of 19. Only contact hydrogen atoms are shown.

interactions such as C−H···X hydrogen bonds, together with intermolecular π···π and C−H···π interactions also present, contribute in a cooperative manner to the 3D expansion of the structures. As can be seen in the histograms of Figure 13, illustrating the orientation of the phenyl rings relative to the imidazole ring of the ligands of all compounds studied in this work, there is enough flexibility either to help the minimization of steric hindrance or to facilitate the effective formation of synthons in the course of molecular assembly. We have no reason to believe that this particular research area is exhausted of new results. As far as feature perspectives are concerned, NiII and CuII analogues of 1−19 are not known to date, and it is currently not evident if the tectons and synthons are dependent on the particular nature of the 3Dmetal ion; it should be noted that the coordination preferences of NiII (3d8) and CuII (3d9) differ significantly from those of CoII (3d7) and ZnII (3d10) studied in this work. Indeed, ongoing studies are producing different and interesting products, and our belief is that we have scratched only the surface of the metallosupramolecular chemistry of L, HL′, and related ligands.

groups for the implementation of the designed hydrogenbonding scheme. The complexes with L are stabilized by two or more (depending on the structural type [MX2L2] or [ML4]2+, respectively) interligand intramolecular π···π stacking interactions. Furthermore, the molecular assembly is driven by a network of weak C−H···Cl/Br/I/O intermolecular interactions. In most cases, very weak C−H···π intermolecular interactions add to the stability of the resulting 3D crystal architectures. The similarity between the CoII and ZnII crystal structures with L, most of them being isomorphic pairs, confirms and reinforces the drawn conclusions on the significant role of the weak, yet steadily occurring, interactions. In parallel, the effect of the subtle balance among these interactions to the final cohesion of the structures is illustrated in polymorphs 1b and 11b, where lack of the intramolecular π···π stacking pattern leads to 2D assemblies. The construction of the crystalline structures with HL′ is clearly and overall directed (in both CoII and ZnII compounds) by the recurring N−H···X (X = Cl, Br, I, O) hydrogen-bonding synthons regardless of the structural type of the complex formed ([MX2(HL′)2] or [M(HL′)4]2+). The predominant and competitive, where necessary, role of the synthons is manifested through diversification in the crystal structures. For example, the lack of characteristic intramolecular π···π interactions (observed in complexes with L), the anti orientation of the ligands in the structures of 9 and 18, and the variation of incorporated solvents could be attributed to the priority for synthon formation at the expenses of other structural parameters. In parallel, the perchlorate in structures 10 and 19 can be regarded as ion template responsible for the formation of the skeleton of these structures. Then, weak

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EXPERIMENTAL SECTION

Materials and Instruments. Chemicals (reagent grade) were purchased from Merck and Alfa Aesar. All manipulations were performed under aerobic conditions using materials and solvents as received; water was distilled in-house. The ligand 1-methyl-4,5diphenyl-1H-imidazole (L) was synthesized as already described in a previous work.27 Microanalyses (C, H, N) were performed by the University of Ioannina (Greece) Microanalytical Laboratory using an EA 1108 Carlo Erba analyzer. IR spectra were recorded on a PerkinElmer PC 16 FT-IR spectrometer with samples prepared as KBr 440



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Figure 13. Ligand flexibility. The representation of the mean planes angles (along the x-axis) formed by phenyl rings 2 and 3 with respect to the imidazole ring 1 for the free ligands as well as for the coordinated ligands of the 21 complexes studied. pellets. Safety note: Perchlorate salts are potentially explosive; such compounds should be synthesized and used in small quantities and treated with utmost care at all times. Synthesis of [CoCl2L2] (1a). A solution of L (0.149 g, 0.63 mmol) and CoCl2 (0.033 g, 0.25 mmol) in EtOH/TEOF (28 mL/2 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, blue prismatic crystals of 1a were obtained after 1 day; yield ca. 40% [based on cobalt(II)]. Anal. calcd for 1a: C, 64.23; H, 4.72; N, 9.36%. Found: C, 64.39; H, 4.57; N, 9.48%. Selected IR bands (KBr, cm−1): 1620 m, 1519s, 1443 m, 1194 m, 1077 m, 787s, 651 m. Synthesis of [CoCl2L2] (1b). This compound was synthesized by a solvothermal reaction of L (0.060 g, 0.25 mmol) and CoCl2 (0.013 g, 0.10 mmol) in EtOH (8 mL). The resultant solution was heated at 150 °C in a Teflon-lined stainless steel autoclave for 3 days. The reaction system was then slowly cooled (5 °C/h) to room temperature. Blue prismatic crystals of 1b were obtained in a 60% yield [based on cobalt(II)]. Anal. calcd for 1b: C, 64.23; H, 4.72; N, 9.36%. Found: C, 64.36; H, 4.52; N, 9.24%. Selected IR bands (KBr, cm−1): 1602 s, 1520 s, 1442 m, 1192 m, 1074w, 786 m, 652 m. Synthesis of [CoBr2L2] (2). A solution of L (0.060 g, 0.25 mmol) and CoBr2 (0.022 g, 0.10 mmol) in EtOH/TEOF (28 mL/2 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, blue prismatic crystals of 2 were obtained after 1 day, in a 40% yield [based on cobalt(II)]. Anal. calcd for 2: C, 55.92; H, 4.11; N, 8.15%. Found: C, 55.74; H, 4.31; N, 8.26%. Selected IR bands (KBr, cm−1): 1602 w, 1516 m, 1442 m, 1194 m, 1074w, 787s, 648 m. Synthesis of [CoI2L2] (3). A solution of L (0.293 g, 1.25 mmol) and CoI2 (0.156 g, 0.50 mmol) in EtOH/TEOF (20 mL/3 mL) was refluxed for 1 h. The resultant blue solution was layered with Et2O (20 mL) to produce blue prismatic crystals in 1 day; yield ca. 50% [based

on cobalt(II)]. Anal. calcd for 3: C, 49.19; H, 3.61; N, 7.17%. Found: C, 49.33; H, 3.42; N, 7.29%. Selected IR bands (KBr, cm−1): 1516 m, 1318 w, 1192 w, 1072 w, 698 s, 648 m. Synthesis of [Co(NO2)2L2] (4). Co(ClO4)2·6H2O (0.183 g, 0.50 mmol) and L (0.293 g, 1.25 mmol) were dissolved in MeOH (5 mL). To the resulting blue solution, NaNO2 (0.086 g, 1.25 mmol) in MeOH (10 mL) was added dropwise. The reaction solution was filtered. Upon slow evaporation of the filtrate, dark pink blocks appeared after 3 days in a 40% yield [based on cobalt(II)]. Anal. calcd for 4: C, 62.04; H, 4.56; N, 13.56%. Found: C, 62.21; H, 4.36; N, 13.41%. Selected IR bands (KBr, cm−1): 1518 s, 1318 w, 1192 s, 1156 s, 1124 s, 1074 s, 786 s, 774 s, 698 s. S y n t h e s i s o f [ C o L 4 ] ( C l O 4 ) 2· 1 . 2 6 M e O H · 0 . 7 4 H 2 O (5·1.26MeOH·0.74H2O). This compound was synthesized by a solvothermal reaction of L (0.298 g, 1.25 mmol) and Co(ClO4)2·6H2O (0.183 g, 0.50 mmol) in MeOH (8 mL). The reaction procedure was similar to that of 1b. Violet prismatic crystals of 5·1.26MeOH·0.74H2O were obtained in a 60% yield (based on L). Anal. calcd for 5·H2O: C, 63.37; H, 4.82; N, 9.24%. Found: C, 63.47; H, 4.62; N, 9.41%. Selected IR bands (KBr, cm−1): 1522 m, 1100 s, 1072 s, 788 m, 774 s, 700 s, 624 m. Synthesis of [CoCl2(HL′)2]·2CH2Cl2·H2O (6·2CH2Cl2·H2O). This compound was synthesized by a solvothermal reaction (100 °C) of HL′ (0.055 g, 0.25 mmol) and CoCl2 (0.013 g, 0.10 mmol) in CH2Cl2 (8 mL). The reaction procedure was similar to that of 1b. Blue prismatic crystals were obtained in a 30% yield [based on cobalt(II)]. Anal. calcd for 6·H2O: C, 61.24; H, 4.53; N, 9.52%. Found: C, 61.39; H, 4.32; N, 9.37%. Selected IR bands (KBr, cm−1): 1508 m, 1490 m, 1074 w, 764 s, 696 s, 648 m. Synthesis of [CoBr2(HL′)2]·CH2Cl2 (7·CH2Cl2). CoBr2 (0.438 g, 2.00 mmol) in MeOH (25 mL) was treated with solid HL′ (0.220 g, 1.00 mmol), and the reaction mixture was refluxed for 1 h. The 441



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and Zn(ClO4)2·6H2O (0.074 g, 0.20 mmol) in Me2CO (8 mL). The reaction procedure was similar to that of 1b. The reaction solution was stored in a closed flask at room temperature. Colorless prismatic crystals were obtained in a 50% yield (based on L). Anal. calcd for 15: C, 63.98; H, 4.70; N, 9.33%. Found: C, 63.74; H, 4.53; N, 9.46%. Selected IR bands (KBr, cm−1): 1524 m, 1384 m, 1098 s, 788 m, 776 s, 700 s, 624 m. Synthesis of [ZnCl2(HL′)2]·H2O (16·H2O). A solution of HL′ (0.275 g, 1.25 mmol) and ZnCl2 (0.068 g, 0.50 mmol) in CH2Cl2 (20 mL) was refluxed for 1 h. The reaction solution was stored in a closed flask at room temperature. Colorless blocks were obtained after 1 day in a 40% yield [based on zinc(II)]. Anal. calcd for 16·H2O: C, 60.57; H, 4.41; N, 9.42%. Found: C, 60.72; H, 4.59; N, 9.58%. Selected IR bands (KBr, cm−1): 1508 m, 1488 m, 1444 m, 1370 m, 1130 m, 1072 m, 976 m, 764 s, 694 s, 648 m. Synthesis of [ZnBr2(HL′)2]·CH2Cl2 (17·CH2Cl2). A solution of HL′ (0.275 g, 1.25 mmol) and ZnBr2 (0.113 g, 0.50 mmol) in CH2Cl2 (20 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, colorless blocks of 17·CH2Cl2 were obtained after 3 days in a 50% yield [based on zinc(II)]. Anal. calcd for 17: C, 54.12; H, 3.63; N, 8.42%. Found: C, 54.23; H, 3.52; N, 8.51%. Selected IR bands (KBr, cm−1): 1510 m, 1488 m, 1444 m, 1368 w, 1130 w, 1074 w, 974 m, 764 s, 696 s, 644 m. Synthesis of [Zn(NO3)2(HL′)2] (18). A solution of HL′ (0.275 g, 1.25 mmol) and Zn(NO3)2·4H2O (0.131 g, 0.50 mmol) in EtOH (20 mL) was stirred for 30 min. The colorless solution was left to slowly evaporate at room temperature. Colorless rods were obtained in 2 days; yield ca. 60% [based on zinc(II)]. Anal. calcd for 18: C, 57.20; H, 3.84; N, 13.34%. Found: C, 57.34; H, 3.63; N, 13.42%. Selected IR bands (KBr, cm−1): 1590 w, 1426 s, 1384 s, 1300 s, 1132 w, 768 s, 694 m, 644 m. Synthesis of [Zn(HL′) 4 ](ClO 4 ) 2 ·2EtOH·2CHCl 3 ·H 2 O (19·2EtOH·2CHCl3·H2O). A solution of HL′ (0.441 g, 2.0 mmol) and Zn(ClO4)2·6H2O (0.186 g, 0.50 mmol) in CHCl3/EtOH (25 mL/ 2 mL) was stirred for 2 h. The colorless solution was layered with nhexane (20 mL) to produce colorless blocks of 19·2EtOH·2CHCl3·H2O after 4 days in a 40% yield [based on zinc(II)]. Anal. calcd for 19·H2O: C, 61.94; H, 4.33; N, 9.63%. Found: C, 61.78; H, 4.19; N, 9.54%. Selected IR bands (KBr, cm−1): 1510 m, 1494 m, 1311 w, 1120 s, 1091 s, 765 s, 696 s, 644 m. Crystallization of L and HL′. Solutions of L (0.293 g, 1.25 mmol) in MeOH (10 mL) and HL′ (0.275 g, 1.25 mmol) in EtOH (10 mL) were prepared and left to slowly evaporate at room temperature. After several days, prismatic crystals of L and HL′ were obtained in a ∼20% yield. Anal. calcd for L: C, 82.02; H, 6.02; N, 11.96%. Found: C, 82.13; H, 6.24; N, 11.82%. Selected IR bands (KBr, cm−1) for L: 3040 w, 1600 s, 1506 s, 1480 s, 1442 s, 1194 m, 772 s, 700 s, 648 s. Anal. calcd for HL′: C, 81.79; H, 5.49; N, 12.72%. Found: C, 81.67; H, 5.61; N, 12.63%. Selected IR bands (KBr, cm−1) for HL′: 3056 w, 2990 w, 2818 w, 2636 w, 1604 s, 1512 s, 1460 s, 1072 m, 954 s, 760 s, 698 s, 650 m. X-ray Crystallography. Suitable single-crystals were covered with paratone-N oil and attached on the tip of glass fibers. Data were collected (ω- and φ-scans) with an Xcalibur-3 and a SuperNova A Oxford Diffraction diffractometers under a flow of nitrogen gas at 100(2) K using Mo Kα radiation (λ = 0.7107 Å) except for compounds 9 and 19 where Cu Kα (λ = 1.5418 Å) was used. Data were collected and processed by the CRYSALIS CCD and RED software,28 respectively. The reflection intensities were corrected for absorption by the multiscan method. All structures were solved using SIR9229 and SHELXS-9730 and refined by full-matrix least-squares on F2 using SHELXL-97.31 All non-H atoms were refined anisotropically, and carbon-bound H-atoms were introduced at calculated positions and allowed to ride on their carrier atoms. All imidazole H-atom on the pyrrolic type N1 atom of the HL′-containing compounds, as well as the hydroxyl H-atoms of solvents in compounds 5 (H2O, MeOH), 6, 10 and 16 (H2O), and 19 (H2O, EtOH) were located in difference Fourier maps and refined isotropically applying soft distance restraints. The structures of 9 and 18 were refined as nonmerohedral twins with an 81:19 and 60:40 twin components ratio, respectively. The nitrite ligand O1−N1−O2 in complex 14 is disordered and has been

resulting solution was cooled down to room temperature, and a blue precipitate formed. Dissolution of the precipitate in CH2Cl2 (8 mL) produced a blue solution, which was left to slowly evaporate at room temperature. Blue plates formed within 4 days; yield ca. 30% (based on HL′). Anal. calcd for 7: C, 54.65; H, 3.67; N, 8.50%. Found: C, 54.43; H, 3.46; N, 8.68%. Selected IR bands (KBr, cm−1): 1508 m, 1272 s, 776 s, 764 s, 722 m, 696 s, 642 s. Synthesis of [CoI(HL′)3]I (8). A solution of HL′ (0.275 g, 1.25 mmol) and CoI2 (0.156 g, 0.50 mmol) in CH2Cl2 (20 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, blue prismatic crystals of 8 were obtained after 4 days; yield ca. 40% (based on HL′). Anal. calcd for 8: C, 55.52; H, 3.73; N, 8.63%. Found: C, 55.35; H, 3.51; N, 8.74%. Selected IR bands (KBr, cm−1): 1624 m, 1517 s, 1441 m, 1190 m, 1077 s, 784 s, 653 m. Synthesis of [Co(NO3)2(HL′)2] (9). A solution of HL′ (0.088 g, 0.40 mmol) and Co(NO3)2·6H2O (0.233 g, 0.80 mmol) in EtOH/ TEOF (20 mL/3 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, dark pink plates of 9 were obtained after 43 days; yield ca. 15% (based on HL′). Anal. calcd for 9: C, 57.79; H, 3.88; N, 13.48%. Found: C, 57.61; H, 3.61; N, 13.59%. Selected IR bands (KBr, cm−1): 1604 w, 1590 w, 1466 s, 1384 s, 1296 s, 768 s, 694 m, 642 m. S y n t h e s i s o f [ C o ( H L ′ ) 4 ] ( C l O 4 ) 2· 1 . 7 M e 2 C O · H 2 O (10·1.7Me2CO·H2O). A solution of HL′ (0.441 g, 2.00 mmol) and Co(ClO4)2·6H2O (0.183 g, 0.50 mmol) in Me2CO (20 mL) was stirred for 30 min. The resultant purple solution was layered with Et2O (20 mL) to produce dark pink prismatic blocks in 3 days; yield ca. 40% [based on cobalt(II)]. Anal. calcd for 10·H2O: C, 52.23; H, 4.36; N, 9.59%. Found: C, 52.41; H, 4.18; N, 9.68%. Selected IR bands (KBr, cm−1): 1508 m, 1490 m, 1318 w, 1120 s, 1090 s, 764 s, 696 s, 648 m. Synthesis of [ZnCl2L2] (11a) and [ZnCl2L2] (11b). A solution of L (0.293 g, 1.25 mmol) and ZnCl2 (0.034 g, 0.25 mmol) in EtOH/ TEOF (25 mL/2 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate colorless prisms of 11b formed after 1 day [20% yield based on zinc(II)], whereas colorless plates of 11a formed after 26 days [60% yield based on zinc(II)]. Anal. calcd for 11a: C, 63.54; H, 4.67; N, 9.25%. Found: C, 63.38; H, 4.41; N, 9.36%. Selected IR bands for 11a (KBr, cm−1): 1522 s, 1508 s, 1324 w, 1194 m, 978 m, 786 s, 772 s, 700 s. Anal. calcd for 11b: C, 63.54; H, 4.67; N, 9.25%. Found: C, 63.31; H, 4.37; N, 9.39%. Selected IR bands for 11b (KBr, cm−1): 1521 s, 1503 s, 1328 w, 1194 m, 977 m, 785 s, 772 s, 703 s. Synthesis of [ZnBr2L2] (12). A solution of L (0.146 g, 0.63 mmol) and ZnBr2 (0.056 g, 0.25 mmol) in EtOH/TEOF (25 mL/2 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, colorless prismatic crystals of 12 were obtained after 1 day in a 40% yield [based on zinc(II)]. Anal. calcd for 12: C, 55.40; H, 4.07; N, 8.08%. Found: C, 55.27; H, 4.21; N, 8.26%. Selected IR bands (KBr, cm−1): 1518 s, 1484 m, 1442 m, 1320 w, 1194 m, 948 m, 786 s, 772 s, 700 s, 652 m. Synthesis of [ZnI2L2] (13). A solution of L (0.293 g, 1.25 mmol) and ZnI2 (0.160 g, 0.50 mmol) in MeOH/TEOF (20 mL/3 mL) was refluxed for 1 h. The reaction solution was filtered. Upon slow evaporation of the filtrate, colorless prismatic crystals of 13 were obtained after 2 days in a 60% yield [based on zinc(II)]. Anal. calcd for 13: C, 48.79; H, 3.58; N, 7.11%. Found: C, 48.53; H, 3.31; N, 7.23%. Selected IR bands (KBr, cm−1): 1518 m, 1482 w, 1440 w, 1318 w, 1192 w, 786 m, 774 m, 698 s, 648 m. Synthesis of [Zn(NO2)2L2] (14). Zn(ClO4)2·6H2O (0.186 g, 0.50 mmol) and L (0.293 g, 1.25 mmol) were dissolved in MeOH (15 mL). To the resulting solution, NaNO2 (0.086 g, 1.25 mmol) in MeOH (10 mL) was added dropwise. The reaction solution was filtered. Upon slow evaporation of the filtrate, colorless prismatic crystals of 14 were obtained after 2 days in a 50% yield [based on zinc(II)]. Anal. calcd for 14: C, 61.40; H, 4.51; N, 13.42%. Found: C, 61.58; H, 4.34; N, 13.31%. Selected IR bands (KBr, cm−1): 1518 s, 1484 m, 1442 m, 1322 w, 1156 s, 1124 s, 1090 s, 1074 s, 978 m, 786 s, 774 s, 700 s, 654 m. Synthesis of [ZnL4](ClO4)2·Me2CO (15·Me2CO). This compound was synthesized by a solvothermal reaction of L (0.117 g, 0.50 mmol) 442



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modeled over two orientations: O1−N11−O21 and O1−N12−O22 with a 70:30 domain ratio, respectively. In the structure of 5, the solvent site close to the perchlorate counterion is disordered and was modeled as 63% MeOH and 37% H2O after detailed competitive refinement. The crystal structure of 8 contains an area of disordered solvent (dichloromethane and water molecules) and that of 10 a disordered acetone molecule with partial occupancy; attempts to model them with a chemically reasonable geometry were unsuccessful. Therefore, the SQUEEZE procedure of PLATON32 was employed to remove the contribution of the electron density associated with those solvent molecules from the intensity data. Geometric/crystallographic calculations were carried out using PLATON,32 OLEX2,33 and WINGX34 packages; molecular/packing graphics were prepared with DIAMOND35 and MERCURY.36 Crystallographic information (cif files) for each of the crystal structure determinations have been deposited at the CCDC (numbers 845564− 845586).

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(6) (a) Blake, A. J.; Champness, N. R.; Hubberstey, P.; Li, W. S.; Withersby, M. A.; Schröder, M. Coord. Chem. Rev. 1999, 183, 117− 138. (b) Robson, R. Dalton Trans. 2000, 3735−3744. (c) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629−1658. (7) (a) Meléndez, R. E.; Hamilton, A. D. Top. Curr. Chem. 1998, 198, 97−129. (b) Aakeröy, C. B.; Beatty, A. M. Aust. J. Chem. 2001, 54, 409−421. (c) Burrows, A. D. Struct. Bonding (Berlin) 2004, 108, 5595. (8) Janiak, C. Dalton Trans. 2000, 3885−3896. (9) (a) Steed, J. W.; Atwood, J. L. In Supramolecular Chemistry; Wiley: Chichester, 2009. (b) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311−2327. (10) Steel, P. G. Coord. Chem. Rev. 1990, 106, 227−265. (11) Constable, E. C. In Metals and Ligand Reactivity: An Introduction to the Organic Chemistry of Metal Complexes; Verlag Chemie: Weinheim, 1996. (12) Kraatz, H.-B.; Metzler-Nolte, N. Concepts and Models in Bioinorganic Chemistry; Wiley-VCH: Weinheim, 2006. (13) Lippard, S. J.; Berg, J. M. Principles of Bioinorganic Chemistry; University Science Books: Mill Valley, CA, 1994. (14) (a) Raptopoulou, C. P.; Paschalidou, S.; Pantazaki, A. A.; Terzis, A.; Perlepes, S. P.; Lialiaris, T.; Bakalbassis, E. G.; Mrozinski, J.; Kyriakidis, D. A. J. Inorg. Biochem. 1998, 71, 15−27. (b) Zanias, S.; Papaefstathiou, G. S.; Raptopoulou, C. P.; Papazisis, K. T.; Vala, V.; Zambouli, D.; Kortsaris, A. H.; Kyriakidis, D. A.; Zafiropoulos, T. F. Bioinorg. Chem. Appl. 2010, 2010, Article ID 168030 (10 pp). (15) Hadzovic, A.; Song, D. Organometallics 2008, 27, 1290−1298. (16) (a) Kounavi, K. A.; Papatriantafyllopoulou, C.; Tasiopoulos, A. J.; Perlepes, S. P.; Nastopoulos, V. Polyhedron 2009, 28, 3349−3355. (b) Kounavi, K. A.; Manos, M. J.; Tasiopoulos, A. J.; Perlepes, S. P.; Nastopoulos, V. Bioinorg. Chem. Appl. 2010, 2010, Article ID 178034 (7 pp). (17) (a) Yang, X.-J.; Drepper, F.; Wu, B.; Sun, W.-H.; Haehnel, W.; Janiak, C. Dalton Trans. 2005, 256−267. (b) Chłopek, K.; Bill, E.; Weyhermüller, T.; Wieghardt, K. Inorg. Chem. 2005, 44, 7087−7098. (18) (a) Bernstein, J.; Hagler, A. T. Mol. Cryst. Liq. Cryst. 1979, 50, 223−234. (b) Aakeröy, C. B. Acta Crystallogr. 1997, B53, 569−586. (19) Stibrany, R. T.; Potenza, J. A.; Schugar, H. J. Private Communication (CCDC 172750) to the Cambridge Structural Database: Cambridge, United Kingdom, 2001. (20) Stibrany, R. T; Schugar, H. J.; Potenza, J. A. Acta Crystallogr. 2004, E60, o1182−o1184. (21) Benisvy, L.; Blake, A. J.; Collison, D.; Davies, E. S.; Garner, C. D.; McInnes, E. J. L.; McMaster, J.; Whittaker, G.; Wilson, C. Chem. Commun. 2001, 1824−1825. (22) Benisvy, L.; Blake, A. J.; Collison, D.; Davies, E. S.; Garner, C. D.; McInnes, E. J. L.; McMaster, J.; Whittaker, G.; Wilson, C. Dalton Trans. 2003, 1975−1985. (23) Kleywegt, G. J.; Wiesmeijer, W. G. R.; Van Driel, G. J.; Driessen, W. L.; Reedijk, J.; Noordik, J. H. Dalton Trans. 1985, 2177−2184. (24) Addison, C. C.; Logan, N.; Wallwork, S. C.; Garner, C. D. Q. Rev. Chem. Soc. 1971, 25, 289−322. (25) (a) Etter, M. C. Acc. Chem. Res. 1990, 23, 120−126. (b) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N.-L. Angew. Chem., Int. Ed. 1995, 34, 1555−1573. (26) (a) Raehm, L.; Mimassi, L.; Guyard-Duhayon, C.; Amouri, H. Inorg. Chem. 2003, 42, 5654−5659. (b) Desmarets, C.; Policar, C.; Chamoreau, L.-M.; Amouri, H. Eur. J. Inorg. Chem. 2009, 4396−4400. (c) Amouri, H.; Mimassi, L.; Rager, M. N.; Mann, B. E.; GuyardDuhayon, C.; Raehm, L. Angew. Chem., Int. Ed. 2005, 44, 4543−4546. (d) Amouri, H.; Desmarets, C.; Bettoschi, A.; Rager, M. N.; Boubekeur, K.; Rabu, P.; Drillon, M. Chem.Eur. J. 2007, 13, 5401−5407. (e) Campos-Fernández, S. C.; Schottel, B. L.; Chifotides, H. L.; Bera, J. K.; Bacsa, J.; Koomen, J. M.; Russell, D. H.; Dunbar, K. R. J. Am. Chem. Soc. 2005, 127, 12909−12923. (f) Yang, X.; Knobler, C. B.; Zheng, Z.; Hawthorne, M. F. J. Am. Chem. Soc. 1994, 116, 7142−7159. (27) McMaster, J.; Beddoes, R. L.; Collison, D.; Eardley, D. R.; Helliwell, M.; Garner, C. D. Chem.Eur. J. 1996, 2, 685−693.

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic information files (CIFs) of all reported structures, molecular overlay figures, and tables with hydrogen-bonding and π···π stacking interactions geometries. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +30 2610 962953. Fax: +30 2610 997118. E-mail: [email protected].

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ACKNOWLEDGMENTS This work was supported by the Research Committee of the University of Patras, Greece (K. Caratheodory Program, Grant No. C.585 to V.N.). Expert advice and helpful suggestions from Professor S. P. Perlepes are greatly acknowledged.

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REFERENCES

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