from non-covalent to covalent multicentric bonding - ACS Publications

Subscriber access provided by Gothenburg University Library

Review

Contribution of different crystal packing forces in #stacking: from non-covalent to covalent multicentric bonding Kresimir Molcanov, Valentina Milasinovic, and Biserka Kojic-Prodic Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00540 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 27, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Contribution of different crystal packing forces in πstacking: from non-covalent to covalent multicentric bonding

Krešimir Molčanov*, Valentina Milašinović and Biserka Kojić-Prodić

AUTHOR ADDRESS Rudjer Bošković Institute, Bijenička 54, Zagreb, Croatia. E-mail: [email protected]

KEYWORDS π-interactions, aromatic, non-aromatic, multicentric covalent bonding'pancake' bonding, crystal engineering

ABSTRACT The present review is aimed to compare crystal packing interactions contributing to stacking arrangements of primarily non-aromatic systems referring only

ACS Paragon Plus Environment

1

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 97

briefly to classical aromatic stacking. The classical aromatic stacking is mainly based on a weak dispersion interactions (E ≤ 1 kcal mol-1) whereas heteroaromatics reveal more electrostatic (or specifically dipolar) contributions (E = 5-10 kcal mol-1). Based mainly on our charge density studies and DFT calculations, the results show that: i) all planar rings stack, regardless of aromaticity (or delocalization of π electrons), and ii) stacking interactions cover a wide continuum ranging from weak, mainly dispersion interactions (E < 5 kcal mol-1) to unlocalized two-electron multicentric (2e/mc) covalent bonds ('pancake bonds', E > 15 kcal mol-1). Our recent studies showed that quinones form face-to-face stacks and the energies of interactions exceed 10 kcal mol-1; ours and other authors' results indicate that interactions between planar radicals involve a significant contribution of covalent bonding. Thus, π-interactions cover a broad range of energies, ranging from ≤ 1 kcal mol-1 to ≥ 20 kcal mol-1, and the interactions span from weak dispersion to multicentric covalent bonding. Therefore, development of a universal model of stacking is needed. In this respect, stacking can be compared to hydrogen bonding, which also ranges between dispersion (weakest hydrogen bonds, such as C-H∙∙∙S and C-H∙∙∙Cl)


2

Page 3 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and two-electron/three-centric covalent bonding (the strongest "symmetrical" hydrogen bonds).

1. INTRODUCTION

π-Stacking, known under a variety of names, π∙∙∙π interaction, π-interaction, πstacking, stacking interaction, aromatic interaction, σ∙∙∙π interaction, aromatic∙∙∙aromatic interaction, aryl interaction, etc., is usually considered as weak interaction, which occurs between aromatic rings. It is a well-known and well-studied type of intermolecular interaction, which had made its way into textbooks of supramolecular chemistry.[1,2] It is usually considered as weak (E ≤ 1 kcal mol-1) and of secondary importance in crystal packing (since it is usually dominated by stronger interactions, such as hydrogen or halogen bonding). Nevertheless, it is commonly present in crystal packings of aromatic compounds[1-6] and double helix of DNA.[5] It also participates in molecular recognition[6-8] and can be used for catalyst design[9].


3


Page 4 of 97

The first phenomena related to stacking were observed in mid-1930's: porphyrins and similar large planar molecules comprising multiple aromatic rings form some kind of layer-like structures in aqueous solutions.[10] However, state-of-the art of the time did not allow a more detailed picture of these layers. The first organic structure with stacked organic rings were published roughly at the same time,[11-14] but it was too early to state whether such motives are common or not. Describing crystal packing of a co-crystal with stacked dimers of p-iodoaniline and trinitrobenzene in 1943, Powell et al.[11] stated that "whether this particular approach of the two molecules has any special significance, or is merely incidental to the packing of a selected pair of molecules, may be settled by detailed determination of similar structures". The model of stacking through interactions of delocalized π electron systems originated in the early 1950's.[15] Amount of experimental evidence grew quickly, particularly by X-ray crystallography; the 2019 version of the Cambridge Structural Database[16] reveals over 741100 symmetryindependent six-membered and 65300 five-membered aromatic and heteroaromatic rings. They form more than 140000 and 6636 stacking-like contacts (selected by centroid separation shorter than 4.1 Å), respectively.


4

Page 5 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


However, the nature of stacking interaction remained elusive for decades. The earliest studies dating back to the 1930's indicated a possible charge transfer,[10,15] and these models later morphed into overlap of π orbitals; however, the existence of attractive interactions with overlapping π-electron clouds has been criticized and challenged.[6,17,18] A fanciful interpretation of stacking was that the attraction is due to interaction of weak magnetic moments created by "ring currents" in aromatic π systems. Unfortunately, the only evidence supporting this model is chemical shifts of protons bound to aromatic rings observed in 1H NMR, while aromatic molecules are diamagnetic as should be expected for closed-shell chemical systems. Some authors dismiss all abovementioned models and claim that stacking of aromatic rings is nothing but dispersion.[17] The rationale is simple and difficult to dispute: dispersion interactions between two large flat surfaces (of aromatic rings) must be much stronger than between two small spherical atoms. Indeed, dispersion is at least non-negligible, if not very important, component of the total interaction, even in the case of very short contacts: while electrostatic forces are proportional to r-2, the dispersion is proportional to r-6, i.e. it is much stronger at short separations.


5


Page 6 of 97

The most convenient and generally accepted model describing aromatic stacking was proposed by Hunter and Sanders in 1990 [18] and has been somewhat refined over the time by taking into consideration direct substituent interactions and solvation/desolvation effects.[6,18-22] The aromatic ring can be considered as an electric quadrupole (Scheme 1) and the stacking geometry is such to minimize electrostatic repulsion of electron-rich π systems and maximize attraction between electron-poor σskeleton and electron-rich π-system. Since the electrostatic component is weak, dispersion contribution is considerable and in most cases dominant. Therefore, energetically the most favorable arrangements of the rings are a parallel, offset (which forms the stacks) and T-shaped (which forms the commonly observed herringbonepattern). The Hunter-Sanders model also successfully predicts energetically unfavorable arrangements, such as parallel, face-to-face and has been corroborated by

ca. 147000 intermolecular contacts found in the CSD.[16] Only a handful of outliers are found in energetically unfavorable area, and these have either been forced by stronger interactions (e.g. hydrogen bonding[23]), or they involve a face-to-face contact between an electron-rich and electron-depleted ring (such as hexafluorobenzene).[20]


6

Page 7 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


So far the research on stacking has been performed only on aromatic compounds, however, there is a growing amount of evidence that aromaticity is not necessary for stacking. Non-aromatic rings (those which do not satisfy Hückel's rule of 4n+2 or 4n πelectrons) also stack, and that their geometry is often in disagreement with HunterSanders model. According to recent computational studies, stacking interactions may be stronger between non-aromatic than between aromatic rings.[24,25] This clearly indicates that ring stacking is a broader phenomenon than previously thought and a universal model is needed.

Stacking of organic radicals and charge-transfer compounds is well known and has recently been employed in design of optoelectronics,[26-28] magnetic[29-33] and conductive molecular materials.[34-40] Recent quantum mechanical models proposed that unusually short and strong interactions between planar radicals may have a partial covalent character,[41-50] and this phenomenon has been termed 'pancake bonding'.[46,50]


7


Page 8 of 97

In this review, we will categorize types of stacking based on the dominant interaction: dispersion (the weakest one), electrostatic (medium one) and covalent (the strongest multicentric covalent bonding) exemplified by our research results.

Scheme 1 An aromatic ring can be approximated as an electrical quadrupole: the σbonded skeleton is electron-poor (partial positive charge), while the electron-rich (partial negative charge) π-clouds extend out of the ring plane.

2. WEAK STACKING: DOMINANTLY DISPERSION INTERACTIONS


8

Page 9 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The most common π-stacking interactions are the weak ones with energies mostly below 1 kcal mol-1. The dominant component here is dispersion,[17] with minor electrostatic and/or dipolar contributions. Typically, this type of weak interaction forms stacks of parallel, offset rings, with centroid distances of 3.8 - 4.2 Å, interplanar distances of 3.5 - 4.0 Å and offset 1.4 - 2.2 Å.[18,20] Dispersion-dominated

stacking

includes

the

ubiquitous

aromatic

stacks,[18,20]

heteroaromatics and aromatics with polar substituents (these form somewhat stronger interactions due to a larger dipolar contribution),[19] and also highly charged non-aromatic rings such as dianions of chloranilic[51,52] and bromanilic acid.[53] Weak contacts between pancake-bonded dimers and trimers of planar radicals[54,55] may also be included in this group. An excellent paper on stacking of aromatic rings was published a few years ago by Martinez and Iverson;[20] since then there is nothing new to be added, we discuss the aromatics

briefly,

only.

As

an

example,

we

will

show

charge

density

of

tetrachlorohydroquinone.[54] It can hardly be considered as the prototype of an aromatic compound, and its stacking geometry is not the typical one, but it has all the features of


9


Page 10 of 97

other aromatic stacks. Its electrostatic potential of carbon atoms ring (Fig. 1 a) is relatively uniform and can be approximated as a quadrupole. Despite its large offset (3.36 Å), interplanar separation is 3.40 Å and there are two relatively close contacts between the carbon atoms (3.55 Å). This offset is a consequence of the bulky, electron-rich chlorine substituents, which are also repulsed by the π system of the neighboring ring (Fig. 1 b). Topology of electron density reveals one bonding critical point (3,-1) and one ring critical point (3,+1), with maximum electron density of 0.034 e Å-3. We will also show two curious cases of stacking of N-methylpyridinium cations (Fig. 2 a) found in two polymorphs in its salt with tetrachlorosemiquinone radical anion.[54,56] In the orthorhombic phase, the cations are parallel, aligned almost face-to-face (Fig. 2 c), while in the triclinic one they are antiparallel and offset (Fig. 2 b).[56] Electron density between the rings of cations is surprisingly low (0.018 e Å-3), so these interactions are unlikely to be attractive at all.[54] The crystal packings are dominated by stacking of tetrachlorosemiquinone radical anions (see Section 4.1), whereas a heteroaromatic unit of N-methylpyridinium cations are not in an optimal arrangement for stacking. DFT calculations (B3LYP and M06-2X functionals with the def2-QZVPP basis set) indicate that


10

Page 11 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


interaction between the cations is indeed repulsive: total energy for two stacked cations in the orthorhombic polymorph is +65.7 kcal mol-1 (the dispersion component being only -4.9 kcal mol-1), and in the triclinic polymorph it is +57.1 kcal mol-1 (with dispersion component of -7.1 kcal mol-1). Therefore, these two contacts can serve as a benchmark for a stack without attractive interactions. Energies of weak π-interactions are comparable to weak hydrogen bonds, such as CH···O, C-H···S and C-H···Cl.[57-59] Weak halogen bonds, like C-Cl···O [60] can be compared to these interactions. All of them are dominated by dispersion, and their effect in crystal packing can be pronounced only in an absence of stronger interactions.


11


Page 12 of 97

Figure 1 a) Electrostatic potential of tetrachlorohydroquinone[54] plotted onto an electron density isosurface of 0.5 e Å-3 (red: –0.1, blue: +1.0 e Å-1) aromatic rings, b) arrangement of two stacked rings of tetrachlorohydroquinone.

Figure 2 a) Electrostatic potential of N-methylpyridinium cation[54] plotted onto an electron density isosurface of 0.5 e Å-3; b) pairs of stacked N-methylpyridinium cations in triclinic polymorph of N-MePy·Cl4Q (isolated dimers)[56] and c) orthorhombic polymorph of NMePy·Cl4Q (infinite stacks).[56] Ring centroids are marked by red spheres.

3. MEDUIM STRONG STACKING: DOMINANTLY ELECTROSTATIC AND POLAR INTERACTIONS


12

Page 13 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.1.Dipolar interactions: tetrachloroquinone Like many simple quinones, tetrachloroquinone (chloranil) does not form stacks, but packs in a herringbone fashion (Fig. 3), thus maximizing contact between electron-richest (carbonyl oxygen) and electron-poorest (carbonyl carbon) parts of the molecules.[54] Two symmetry-independent intermolecular C···O contacts can be identified in its crystal packing: i) between antiparallel C=O groups (angle between mean ring planes, α = 0°, C···O distance is 3.13 Å), which is probably assisted by antiparallel local dipoles and ii) a C···O contact with α = 68° and distance of 2.77 Å. Both of these contacts involve a (3,-1) critical point, with maximum electron densities of 0.080 (i) and 0.042 e Å-3 (ii), respectively. While these electron densities are comparable to weaker hydrogen bonds,[59] tetrachlorosemiquinone easily sublimates, so we expect that the interactions are not very strong. Therefore, in this system a competition exists between stacking and dipolar interactions; in contrast, in heteroaromatics, stacking and dipolar interactions are cooperative.[19]


13


Page 14 of 97

Figure 3 Interactions between molecules of tetrachloroquinone:[54] a) electrostatic potential potential plotted onto an electron density isosurface of 0.5 e Å-3 (red: –0.1, blue: +1.0) and b) topology of electron density [bonding critical points (3,-1) are depicted as red dots, ring critical points (3,+1) as light blue and cage critical points (3,+3) as violet].

3.2.

Interactions

of

electrical

multipoles:

face-to-face

stacking

of

2,5-

dihydroxyquinonate (anilate) anions We described perfect face-to-face stacks of hydrogen chloranilate anions (HCA-),[51] hydrogen bromanilate anions (HBA-),[53] 2,5-dihydroxyquinonate dianions[61] and with


14

Page 15 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


stacks comprising sequence ∙∙∙HCA-∙∙∙HCA-∙∙∙H2CA∙∙∙ [62] in their simple alkali salts; in all of them centroid and interplanar separations are about 3.3 Å. This unusually short distance (sum of van der Waals radii for carbon is 3.40 Å) and needle-like morphology of the crystals, which are elongated in the direction of stacking, led us to the conclusion that this type of stacking is unusually strong.[51] Analysis of crystal packings show that HOH···O hydrogen bonds, occurring in almost all of the studied compounds, are of secondary importance. The reason for this face-to-face arrangement is inhomogeneous distribution of electron density in HCA- and HBA- rings, with alternating electron-rich π bonds (double and delocalized) and electron-poor σ bonds (single ones) (Fig. 4). Our in-depth study of the model system, KHCA·2H2O, by a combination of X-ray charge density and quantum chemistry[63] reveal that energy of this face-to-face stacking is comparable to medium-strong hydrogen bonds, such as O-H···O and O-H···N.[58] Electrostatic potential in a pair of rings (Fig. 4) showed an excellent fit of electron-rich and electron-depleted areas of two contiguous rings, which maximizes electrostatic attraction, and minimizes repulsion. Topology of electron density revealed seven (3,-1) bond critical points between the rings, and also a (3,+3) cage critical point (i.e. a local minimum of


15


Page 16 of 97

electron density, pointing out to a cage-like distribution of electron density). However, low electron density of only 0.05 e Å-3 indicates a closed-shell interaction. Quantum chemical calculations of isolated clusters by MP2 and simulation of crystal lattice by periodic DFT estimate the energy of the stacking interaction to be greater than 10 kcal mol-1; that is, stronger than typical O-H···O hydrogen bonds.[63] Stronger halogen bonds, N-Br···N and N-I···N [64] are also of comparable strength, often exceeding 10 kcal mol-1.

Figure 4 a) Schematic drawing of a pair of stacked hydrogen chloranilate dianions from KHCA·2H2O indicates overlap of electron-poor σ bonds C-H and electron-rich π bonds C-O. b) Electrostatic potential an electron density isosurface of 0.5 e Å-3 (red: –0.1, blue:


16

Page 17 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


+1.0 e Å-1) shows excellent fit between electron-rich areas of one ring (red, orange) and electron-depleted areas of another one (blue).[63]

3.3. Electrostatic interactions between metal-chelate rings It had been noted that metal-chelate rings sometime stack.[65-72] To some authors this was an indication of their aromatic character,[73,74] but aromaticity of the metal-chelate rings, or metalloaromaticity,[75] is a contentious issue.[72,76,77] Quantum chemical calculations by Zarić et al. do not corroborate aromatic character of metal-chelate rings.[77] Metal-ligand bonds are highly polar, and usually represent a borderline case between covalent and ionic. Accurate X-ray charge density studies[78-84] of quite a few metal complexes revealed low electron density at bonding critical points ( 3.6 Å. These data nicely correspond to contacts between the dimers, whose geometry resembles stacking of aromatic rings. Since the energy barrier for electron jumping between such "quasi-closed-shell" dimers is high, crystals with Peierls-distorted stacks are diamagnetic and Mott-type insulators.[41-43] Two types of π-stacks of radicals are known: i) stacks of closely interacting pairs of radicals (also known as Peierls-distorted stacks or pancake bonded pairs) with alternating short (< 3.2 Å) and long (> 3.4 Å) interplanar separation (Fig. 6 a) and ii) stacks of equidistant radicals with interplanar separation of about 3.3 Å (Fig. 6 b). There is a correlation between separation distance and magnetic and electrical properties. Since the pancake bonded (Peierls-distorted) stacks are thermodynamically more stable, they are


22

Page 23 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


also more common, and better studied. Typically, they have coupled spins and are therefore diamagnetic and insulators. Stacks of equidistant radicals are less stable due to the lack of pancake bonding, but are more interesting from a materials chemists' and crystal engineers' point of view. Such structures have long-range (1D) ordering of spin, mostly antiferromagnetic (Fig. 6 b), so interplanar separations are still shorter than the sum of van der Waals radii for carbon, albeit longer than in pancake bonded dimers. Electronic structure of such stacks resembles 1D semiconductors, and energy barrier for electrons jumping between the radicals is often < 1 eV. For ionic radicals, conductivities are typically < 10-6 S cm-1,[3040,56,94,95]

and for some neutral radicals conductivities as high as 10-1 S cm-1 have been

observed.[ 30-40,56,94,95] A few systems were described which display bistability, i.e. ability to switch between diamagnetic and insulator (Peierls-distorted stacks) and antiferromagnetic and semiconductor state (equidistant radicals).[30,39,104] This is one of the directions for design and development of organic electronics, however, possible applications have been out of reach, yet.


23


Page 24 of 97

Figure 6 Two types of stacks of semiquinone radicals: a) Peierls-distorted stacks of radical dimers (alternating longer (>3.5 Å) and shorter ( 15 kcal mol-1). In this regard, stacking is similar to hydrogen and halogen bonding, the difference being that the latter two form local bonds, while the former is not localized. Like hydrogen

[58,134]

and halogen bonds,[64,135] stacking interactions can be roughly

separated into three categories based on the dominant contribution to the total interaction. The weakest, dispersion-dominated interactions are mostly between aromatic rings. In stronger ones, the main component of the interaction is electrostatic with important contributions of (local) dipolar attraction and dispersion. However, we have to keep in mind that electrostatic forces are proportional to r-2, while dispersion forces are proportional to r-6; therefore, electrostatic interactions are of longer range. The strongest stacking is between planar organic radicals, and here the main interaction is unlocalized covalent one, involving unpaired electrons. Electrostatic contribution is significant, especially in equidistant stacks with weaker long-range ordering. Orientation of the rings and offset are determined mostly by electrostatic attractions and repulsions. The three types of contact between stacked semiquinones and similar planar radicals can be summed up as: 1) strong 'pancake bonds', which are mainly covalent 2e/mc; 2)


44

Page 45 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


intermediate weak 'pancake bonds' with strong electrostatic contribution and long range magnetic ordering, and 3) pancake bonding between trimers of partially charged radicals. Type 1) is the most interesting from the point of theory of chemical bonding, since it represents a borderline between inter- and intramolecular interactions (similar to strong hydrogen bonding), while the type 2) is the most interesting from the applicative point of view, since it results in interesting electrical and magnetic properties. Another likely analogy between stacking and hydrogen bonding is cooperative effect, which is common for hydrogen bonds.[58,135-139] Possibilities of application in crystal engineering and design of functional materials are almost limitless. Face-to-face stacks of quinones occur regularly, whenever they are not sterically inhibited. It also determines crystal morphology: the crystals grow as needles elongated in direction of the stacking.[56,63] Stacks of equidistant radicals determine semiconductivity and magnetic properties, and these can be modified by crystal engineering. Relatively stable systems with conductivities comparable to Si or Ge have already been prepared,[30-40,94,95] as well as organic compounds which are ferromagnetic at very low temperatures.[139] Bistability allows switching of electrical and magnetic


45


Page 46 of 97

properties by external influences (temperature, pressure, irradiation by a certain wavelength).[31,39,102] Strong hydrogen bonds,[58,134,140] strong halogen bonds[72,132,141-143] and 'pancake bonds'[46,50,54,55] stretch the definition of the covalent bond and blur the border between intra- and intermolecular; this may eventually lead to a new definition of the chemical bond.[144,145] It also follows that π-stacking is in fact similar to other two common intermolecular interactions, hydrogen and halogen bonding: as summed up in Table 1, their energies are comparable, and can be phenomenologically classified as mainly dispersion (weak), mainly electrostatic (medium) or partially covalent (strong). The main difference is that the π-stacking is not localized, while hydrogen and halogen bonds are local.

AUTHOR INFORMATION

Corresponding Author


46

Page 47 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


*K. M. E-mail: [email protected]

Author Contributions The manuscript was written through contributions of all authors.

Funding Sources This work was financed by the Croatian Science Foundation, grant no. IP-2014-094079.

Notes Any additional relevant notes should be placed here.

ACKNOWLEDGMENT This work was financed by the Croatian Science Foundation, grant no. IP-2014-094079.

ABBREVIATIONS CCR2, CC chemokine receptor 2; CCL2, CC chemokine ligand 2; CCR5, CC chemokine receptor 5; TLC, thin layer chromatography.


47


Page 48 of 97

REFERENCES [1] Steed, J. W.; Atwood, J. L. Supramolecular Chemistry, 2nd ed., J. Wiley & sons, 2009.

[2] Desiraju, G. R.; Vittal, J. J.: Ramanan, A.Crystal Engineering, A Textbook, World Scientific Publishing, Singapore, 2011.

[3] Tiekink, R. T.; Zukerman-Schpector J. (Eds.), The Importance of π-Interactions in

Crystal Engineering, Wiley, 2012.

[4] Molčanov, K.; Kojić-Prodić, B. Towards understanding π-stacking interactions between non-aromatic rings, IUCrJ, 2019, 6, 156-166.

[5] Mak, C. H. Unraveling Base Stacking Driving Forces in DNA, J. Phys. Chem. B 2016,

120, 6010-6020.

[6] Salonen, L. M.; Ellermann, M.; Diedrich, F. Aromatic Rings in Chemical and Biological Recognition: Energetics and Structures, Angew. Chem., Int. Ed., 2011, 50, 4808-4842.


48

Page 49 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[7] Riley, K. E.; Hobza, P. On the Importance and Origin of Aromatic Interactions in Chemistry and Biodisciplines, Acc. Chem. Res. 2013, 46, 927-936.

[8] Makwana, K. M.; Mahalakshmi, R. Implications of aromatic–aromatic interactions: From protein structures to peptide models, Protein Science, 2015, 24, 1920-1933.

[9] Neel, A. J.; Hilton, M. J.; Sigman, M. S.; Toste F. D. Exploiting non-covalent π interactions for catalyst design, Nature, 2017, 543, 637-646.

[10] Alexander, A. E. Monolayers of porphyrins and related compounds, J. Chem. Soc., 1937, 1813-1816.

[11] Powell, H. M.; Huse, G.; Cooke, P. W. The structure of molecular compounds. Part I. The crystal structure of p-iodoaniline-s-trinitrobenzene, J. Chem. Soc., 1943, 153-157.

[12] Hertel, E.; Römer, G. Z. Phys. Chem., 1933, B22, 77.

[13] Hertel, E.; Römer, G. Z. Der strukturelle Feinbau der Trinitrobenzolderivate, Phys.

Chem., 1933, B22, 267.


49


Page 50 of 97

[14] Hertel, E.; Kleu, H. Z. Kristallstruktur eines neuen Typs von Molekülverbindungen,

Phys. Chem., 1930, B11, 59.

[15] Landauer, J.; McConnel, H. A Study of Molecular Complexes Formed by Aniline and Aromatic Nitrohydrocarbons, J. Am. Chem. Soc., 1952, 74, 1221-1224.

[16] Groom, C. R.; Bruno, I. J.; Lightfoot M. P.; Ward, S. C. The Cambridge Structural Database, Acta Cryst. 2016, B72, 171-179.

[17] Grimme, S. Do Special Noncovalent π–π Stacking Interactions Really Exist?

Angew. Chem., Int. Ed., 2008, 47, 3430-3434.

[18] Hunter, C. A.; Sanders, J. K. M. The Nature of π-π Interactions. J. Am. Chem. Soc., 1990, 112, 5525-5534.

[19] Janiak, C. A critical account on π–π stacking in metal complexes with aromatic nitrogen-containing ligands, Dalton Trans., 2000, 3885-3896.

[20] Martinez, C. L.; Iverson, B. L. Rethinking the term 'π-stacking', Chem. Sci., 2012,

3, 2191-2201.


50

Page 51 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[21] Wheeler, S. E.; Bloom, J. W. G. Toward a More Complete Understanding of Noncovalent Interactions Involving Aromatic Rings, J. Phys. Chem. A 2014, 118, 61336147.

[22] Carini, M.; Ruiz, M. P.; Usabiaga, I.; Fernandez, J. A.; Cocinero, E. J.; MelleFranco, M.; Diez-Perez, I.; Mateo-Alonso, A. High conductance values in π-folded molecular junctions, Nature Commun. 2017, 8, 15195.

[23] Sokolov, A. N.; Friščić, T.; MacGillivray, L. R. Enforced Face-to-Face Stacking of Organic Semiconductor Building Blocks within Hydrogen-Bonded Molecular Cocrystals,

Angew. Chem., Int. Ed., 2006, 128, 2806-2807.

[24] Bloom, J. W. G.; Wheeler, S. E. Taking the aromaticity out of aromatic interactions,

Angew. Chem. Int. Ed. 2011, 50, 7847-7849.

[25] Wheleer, S. Understanding Substituent Effects in Noncovalent Interactions Involving Aromatic Rings, Acc. Chem. Res., 2013, 46, 1029-1038.


51


Page 52 of 97

[26] T. Naito (Ed.), Functional Materials: Advances and Applications in Energy Storage

and Conversion, Pan Stanford Publishing, 2019.

[27] Beldjoudi, Y.; Arauzo, A.; Campo, J.; Gavey, E. L.; Pilkington, M.; Nascimento, M. A.; Rawson, J. M., Structural, Magnetic, and Optical Studies of the Polymorphic 9Anthracenyl Dithiadiazolyl Radical, J. Am. Chem. Soc., 2019, 141, 6875-6889.

[28] Beldjoudi, Y.; Nascimento, M. A.; Cho, Y. J.; Yu, H.; Aziz, H.; Tonuchi, D.; Eguchi, K.; Matsushita, M. M.; Awaga, K.; Osorio-Roman, I.; Constantinides, C. P.; Rawson, J. M., Multifunctional Dithiadiazolyl Radicals: Fluorescence, Electroluminescence, and Photoconducting Behavior in Pyren-1'-yldithiadiazolyl, J. Am. Chem. Soc., 2018, 140, 6260-6270.

[29] Hicks, R. G. Switchable materials: a new spin on bistability, Nature Chem., 2011,

3, 189–191.

[30] Sanvito, S., Molecular spintronics, Chem. Soc. Rev., 2011, 40, 3336–3355.


52

Page 53 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[31] Itkis, M. E.; Chi, X.; Cordes A. W.; Haddon, R. C. Magneto-opto-electronic bistability in a phenalenyl-based neutral radical, Science, 2002, 296, 1443–1445.

[32] Constantinides, C. P.; Berezin, A. A.; Zisimou, G. A.; Manoli, M.; Leitus, G. M.; Bendikov, M.; Probert, M. R.; Rawson, J. M.; Koutentis, P. A., A Magnetostructural Investigation of an Abrupt Spin Transition for 1 ‑ Phenyl-3-trifluoromethyl-1,4dihydrobenzo[e][1,2,4]triazin-4-yl, J. Am.Chem. Soc., 2014, 136, 11906-11909.

[33] Mills, M. B.; Wohlhauser, T.; Stein, B.; Verduyn, W. R.; Song, E.; Dechambenoit, P.; Rouzieres, M.; Clerac, R.; Preuss, K. E., Magnetic Bistability in Crystalline Organic Radicals: The Interplay of H ‑ bonding, Pancake Bonding, and Electrostatics in 4 ‑ (2'Benzimidazolyl)-1,2,3,5-dithiadiazolyl, J. Am. Chem. Soc., 2018, 140, 16904-16908.

[34] Nakano, T. (Ed.) π-Stacked Polymers and Molecules, Springer 2014.

[35] Chen, X.; Gao, F.; Yang, W. Single-Crystal X-ray Structures of conductive πStacking Dimers of Tetrakis(alkylthio)benzene Radical Cations, Sci. Rep. 2016, 6, 29314 doi:10.1038/srep29314.


53


Page 54 of 97

[36] Yu, X.; Mailman, A.; Dube, P. A.; Assoud A.; Oakley, R. T., The first semiquinonebridged bisdithiazolyl radical conductor: a canted antiferromagnet displaying a spin-flop transition, Chem. Commun., 2011, 4655–4657.

[37] Lekin, K.; Winter, S. M.; Downie, L. E.; Bao, X.; Tse, J. S.; Desgreniers, S.; Secco, R. A.; Dube, P. A.; Oakley, R. T., Hysteretic Spin Crossover between a Bisdithiazolyl Radical and Its Hypervalent σ-Dimer, J. Am. Chem. Soc., 2010, 132, 16212–16224.

[38] Yu, X.; Mailman, A.; Lekin, K.; Assoud, A.; Robertson, C. M.; Noll, B. C.; Campana, C. F.; Howard, J. A. K.; Dube, P. A.; Oakley, R. T., Semiquinone-Bridged Bisdithiazolyl Radicals as Neutral Radical Conductors, J. Am. Chem. Soc., 2012, 134, 2264–2275.

[39] Podzorov, V. π-Electron systems: Building molecules for a function, Nature Mater., 2010, 10, 616–617.

[40] Morita, Y.; Murata, T.; Nakasuji, K. Cooperation of Hydrogen-Bond and ChargeTransfer Interactions in Molecular Complexes in the Solid State, Bull. Chem. Soc. Jpn, 2013, 86, 183-197.


54

Page 55 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[41] Huang, J.; Kingsbury, S.; Kertesz, M., Crystal packing of TCNQ anion π-radicals governed by intermolecular covalent π–π bonding: DFT calculations and statistical analysis of crystal structures, Phys. Chem. Chem. Phys. 2008, 10, 2625–2635.

[42] Mou, Z.; Kertesz, M., Pancake Bond Orders of a Series of π-Stacked Triangulene Radicals, Angew. Chem. Int. Ed. 2017, 56, 10188 –10191.

[43] Cui, Z.-H.; Lischka, H.; Beneberu, H. Z.; Kertesz, M. Rotational Barrier in Phenalenyl Neutral Radical Dimer: Separating Pancake and van der Waals Interactions,

J. Am. Chem. Soc., 2014, 136, 5539-5542.

[44] Cui, Z.; Lischka, H.; Mueller, T.; Plasser, F.; Kertesz, M., Study of the Diradicaloid Character in a Prototypical Pancake‐Bonded Dimer: The Stacked Tetracyanoethylene (TCNE) Anion Dimer and the Neutral K2TCNE2 Complex, ChemPhysChem, 2014, 15, 165-178.

[45] Cui, Z.-H.; Lischka, H.; Beneberu, H. T.; Kertesz, M. Double pancake bonds, J.

Am. Chem. Soc., 2014, 136, 12958-12965.


55


Page 56 of 97

[46] Preuss, K. E. Pancake bonds: π-Stacked dimers of organic and light-atom radicals,

Polyhedron, 2014, 79, 1-15.

[47] Huang, J.; Kertesz, M. Intermolecular Covalent π−π Bonding Interaction Indicated by Bond Distances, Energy Bands, and Magnetism in Biphenalenyl Biradicaloid Molecular Crystal, J. Am. Chem. Soc., 2007, 129, 1634-1643.

[48] Tian, Y.-H.; Kertesz, M. Charge Shift Bonding Concept in Radical π-Dimers, J.

Phys. Chem. A, 2011, 115, 13942-13949.

[49] Novoa, J. J.; Stephens, P. W.; Weerasekare, M.; Shum, W. W.; Miller, J. S. The Tetracyanopyrazinide Dimer Dianion, [TCNP]22−. 2-Electron 8-Center Bonding, J. Am.

Chem. Soc., 2009, 131, 9070-9075.

[50] Kertesz, M. Pancake bonding: an unusual pi-stacking interactions, Chem. Eur. J., 2018, 24, 400-416.

[51] Molčanov, K.; Kojić-Prodić, B.; Meden, A. π-Stacking of quinoid rings in crystals of alkali diaqua hydrogen chloranilates, CrystEngComm, 2009, 11, 1407-1415.


56

Page 57 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[52] Molčanov, K.; Kojić-Prodić, B.; Meden, A. Unique electronic and structural properties of 1,4-benzoquinones: crystallochemistry of alkali chloranilate hydrates, Croat.

Chem. Acta, 2009, 82, 387-396.

[53] Molčanov, K.; Kojić-Prodić, B. Face-to-face stacking of quinoid rings of alkali salts of bromanilic acid, Acta Crystallogr. B, 2012, B68, 58-65.

[54] Molčanov, K.; Jelsch, C., Landeros-Rivera, B.; Hernández-Trujillo, J.; Wenger, E.; Stilinović, V.; Kojić-Prodić, B.; Escudero-Adán, E. C. Partially covalent two-

electron/multicentric bonding between semiquinone radicals, Cryst. Growth Des. 19 (2019), 391-402.

[55] Molčanov, K.; Mou, Z.; Kertesz, M.; Kojić-Prodić, B.; Stalke, D.; Demeshko, S.; Šantić, A.; Stilinović, V. Two-electron / multicentre - pancake bonding in 𝝅-stacked trimers in a salt of tetrachloroquinone anion, Chem. Eur. J., 2018, 24, 8292-8297.

[56] Molčanov, K.; Stilinović, V.; Šantić, A.; Maltar-Strmečki, N.; Pajić, D.; Kojić-Prodić, B. Fine tuning of π-stack separation distances of semiquinone radicals affects their magnetic and electric properties, Cryst. Growth Des., 2016, 16, 4777-4782.


57


Page 58 of 97

[57] Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and

Biology, IUCr/Oxford Science Publications, 1999.

[58] Steiner, T. Hydrogen bonding in the solid state, Angew. Chem. Int. Ed., 2002, 41, 48-76.

[59] Munshi, P.; Guru Row, T. N. Evaluation of weak intermolecular interactions in

molecular crystals via experimental and theoretical charge densities, Crystallogr. Rev., 2005, 11, 199-241.

[60] Cavalli, G.; Metrangolo, P.; Milani, R.; Pilati, T.; Priimagi, A.; Resnati, G.; Terraneo, G. The Halogen Bond, Chem. Rev., 2016, 116, 2478-2601.

[61] Molčanov, K.; Kojić-Prodić, B.; Babić, D.; Stare, J. Face-to-face stacking of dianionic quinoid rings in crystals of alkali salts of 2,5-dihydroxyquinone in view of π – system polarization, CrystEngComm, 2013, 15, 135-143.


58

Page 59 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[62] Molčanov, K.; Sabljić, I.; Kojić-Prodić, B. Face-to-face π-stacking in the multicomponent crystals of chloranilic acid, alkali hydrogenchloranilates, and water,

CrystEngComm, 2011, 13, 4211-4217.

[63] Molčanov, K.; Stare, J.; Kojić-Prodić, B.; Lecomte, C.; Dahaoui, S.; Jelsch, C.; Wenger, E.; Šantić, A.; Zarychta, B. A polar/π model of interactions explains face-to-face stacked quinoid rings: a case study in the crystal of potassium hydrogen chloranilate dihydrate, CrystEngComm, 2015, 17, 8645-8656.

[64] Stilinović, V.; Horvat, G.; Hrenar, T.; Nemec, V.; Cinčić, D. Halogen and Hydrogen Bonding between (N‐Halogeno)‐succinimides and Pyridine Derivatives in Solution, the Solid State and In Silico , Chem. Eur. J., 2017, 23, 5244-5257.

[65] Molčanov, K.; Ćurić, M.; Babić, D.; Kojić-Prodić, B. 2D and 3D supramolecular assemblies of double cyclopalladated azobenzenes realized by C-H...Cl-Pd, π···π and CH···π interactions, J. Organomet. Chem., 2007, 692, 3874-3881.


59


Page 60 of 97

[66] Babić, D.; Ćurić, M.; Molčanov, K.; Ilc, G.; Plavec, J. Synthesis and Characterization of Dicylopalladated Complexes of Azobenzene Derivatives by Experimental and Computational Methods, Inorg. Chem., 2008, 47, 10446-10454.

[67] Androš, L.; Jurić, M.; Planinić, P.; Žilić, D.; Rakvin, B.; Molčanov, K. New mononuclear oxalate complexes of copper(II) with 2D and 3D architectures: Synthesis, crystal structures and spectroscopic characterization, Polyherdon, 2010, 29, 1291-1298.

[68] Molčanov, K.; Jurić, M.; Kojić-Prodić, B. Stacking of metal chelating rings with πsystems in mononuclear complexes of copper(II) with 3,6-dichloro-2,5-dihydroxy-1,4benzoquinone (chloranilic acid) and 2,2'-bipyridine ligands, Dalton Trans., 2013, 42, 15756-15765.

[69] Molčanov, K.; Jurić, M.; Kojić-Prodić, B. A novel type of coordination mode of chloranilic acid leading to the formation of polymeric coordination ribbon in the series of mixedligand copper(II) complexes with 1,10-phenanthroline, Dalton Trans., 2014, 43, 7208-7218.


60

Page 61 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[70] Jurić, M.; Molčanov, K.; Žilić, D.; Kojić-Prodić, B. From mononuclear to linear onedimensional coordination species of copper(II)-chloranilate: design and characterization,

RSCAdv, 2016, 6, 62785-62796.

[71] Kravtsov, V. 'Metalloaromaticity' of metal chelate ring. π–π stacking interactions in solid-state supramolecular architecture of copper(II) complexes with aromatic ligands,

Acta Cryst. A, 2004, A60, s304.

[72] Malenov, D. P.; Janjić, G. V.; Medaković, V. B.; Hall, M. B.; Zarić, S. D. Noncovalent bonding: Stacking interactions of chelate rings of transition metal complexes, Coord.

Chem. Rev., 2017, 345, 318-341.

[73] Castiñeiras, A.; Sicilia-Zafra, A. G.; González-Pérez, J. M.; Choquesillo-Lazarte, D.; Niclós-Gutiérrez, J. Intramolecular “Aryl−Metal Chelate Ring” π,π-Interactions as Structural Evidence for Metalloaromaticity in (Aromatic α,α‘-Diimine)−Copper(II) Chelates:

Molecular

and

Crystal

Structure

of

Aqua(1,10-phenanthroline)(2-

benzylmalonato)copper(II) Three-hydrate, Inorg. Chem., 2002, 41, 6956-6958.


61


Page 62 of 97

[74] Karabıyık, H.; Erdem, Ö.; Agyün, M.; Güzel, B.; Gárcia-Granda, S. Ligand-to-Metal Charge

Transfer

Resulting

in

Metalloaromaticity

of

[R,R-Cyclohexyl-1,2-bis(2-

Oxidonaphthylideneiminato-N,N′,O,O′)]Cu(II): A Scrutinized Structural Investigation, J.

Inorg. Organomet. Polym. 2010, 20, 142-151.

[75] Masui, H. Metalloaromaticity, Coord. Chem. Rev., 2001, 219-221, 957-992.

[76] Feixas, F.; Matito, E.; Poater, J.; Solà, M. Metalloaromaticity, WIREs Comput. Mol.

Sci., 2013, 3, 105-122.

[77] Miličić, M. K.; Ostojić, B. D.; Zarić, Are chelate rings aromatic? Calculations of magnetic properties of acetylacetonato and o-benzoquinonediimine chelate rings, Inorg.

Chem., S. D. 2007, 46, 7109-7114.

[78] Chuang, Y. C.; Sheu, C.-F.; Lee, G.-H.; Chen, Y.-S.; Wang, Y. Charge density studies of 3d metal (Ni/Cu) complexes with a non-innocent ligand, Acta Crystallogr. B., 2017, B73, 634-642.


62

Page 63 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[79] Poulsen, R. D.; Bentien, A.; Graber, T.; Iversen, B. B Synchrotron charge-density studies in materials chemistry: 16 K X-ray charge density of a new magnetic metalorganic framework material, [Mn2(C8H4O4)2(C3H7NO)2], Acta Crystallogr. A, 2004, A60, 382-389.

[80] Gajda, R.; Wożniak, K. Charge density studies of an inorganic-organic hybrid pphenylenediammonium tetrachlorocuprate, Struct. Chem., 2017, 28, 1607-1622.

[81] Wang, Y. Charge Density Analysis and Bond Characterization of 3d‐Transition Metal Complexes, J. Chin. Chem. Soc., 2014, 61, 27-38.

[82] Vologzhanina, A. V.; Kats, S. V.; Penkova, L. V.; Pavlenko, V. A.; Efimov, N. N.; Minin, V. V.; Eremenko, I. L. Combined analysis of chemical bonding in a CuII dimer using QTAIM, Voronoi tessellation and Hirshfeld surface approaches, Acta Crystallogr. B, 2015,

B71, 543-554.

[83] Bianchi, R.; Gervasio, G.; Marabello, D. The experimental charge density in transition metal complexes, C. R. Chimie, 2005, 8, 1392-1399.


63


Page 64 of 97

[84] Pillet, S.; Souhassou, M.; Mathonière, C.; Lecomte, C. Electron Density Distribution of an Oxamato Bridged Mn(II)−Cu(II) Bimetallic Chain and Correlation to Magnetic Properties, J. Am. Chem. Soc., 2004, 126, 1219-1228.

[85] Vuković, V.; Molčanov, K.; Jelsch, C.; Wenger, E.; Krawczuk, A.; Jurić, M.; Androš Dubraja, L.; Kojić-Prodić, B. Malleable electronic structure of chloranilic acid and its species determined by X-ray charge density studies, Cryst. Growth Des., 2019, 19, 28022810.

[86] Hirshfeld, F. L. Bonded-atom fragments for describing molecular charge densities,

Theor. Chim. Acta, 1977, 44, 129-137.

[87] Spackman, M. A.; Jayatilaka, D. HIrshfeld surface analysis, CrystEngComm, 2009,

11, 13-32.

[88] 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.


64

Page 65 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[89] Blatov, V. A. Voronoi–dirichlet polyhedra in crystal chemistry: theory and applications, Crystallogr. Rev., 2004, 10, 249-318.

[90] Desiraju, G. R. Crystal Engineering: A Holistic View, Angew. Chem., Int. Ed., 2007,

46, 8342-8356.

[91] Lisac, K.; Topić, F.; Arhangelskis, M.; Cepić, S.; Julien, P. A.; Nickels, C. W.; Morris, A. J.; Friščić, T.; Cinčić, D. Halogen-bonded cocrystallization with phosphorus, arsenic and antimony acceptors, Nature Commun., 2019, 10, 61.

[92] Nemec, V.; Fotović, L.; Friščić, T.; Cinčić, D. A Large Family of Halogen-Bonded Cocrystals Involving Metal–Organic Building Blocks with Open Coordination Sites, Cryst.

Growth Des. 2017, 17, 6169-6173.

[93] Rosokha, S. V.; Kochi, J. K. Molecular and Electronic Structures of the LongBonded π-Dimers of Tetrathiafulvalene Cation-Radical in Intermolecular Electron Transfer and in (Solid-State) Conductivity, J. Am. Chem. Soc. 2007, 129, 828-838.


65


Page 66 of 97

[94] Murata, T.; Yamamoto, Y.; Yakiyama, Y.; Nakasuji, K.; Morita, Y. Syntheses, Redox Properties, Self-Assembled Structures, and Charge-Transfer Complexes of Imidazoleand Benzimidazole-Annelated Tetrathiafulvalene Derivatives, Bull. Chem. Soc. Jpn, 2013, 86, 927-939.

[95] Mercuri, M. L.; Deplano, P.; Pilia, L.; Serpe, A.; Artizzu, F. Interactions modes and physical properties in transition metal chalcogenolene-based molecular materials, Coord.

Chem. Rev. 2010, 254, 1419-1433.

[96] Rosokha, S. V.; Zhang, J.; Lu, J.; Kochi, J. K. Intermolecular π‐dimer of oxoverdazyl radicals with long‐distance multicenter (2e/8c) bonding via nitrogen atoms, J. Phys. Org.

Chem., 2010, 23, 395-399.

[97] Pal, S. K.; Itkis, M. E.; Reed, R. E.; Oakley, R. T.; Cordes, A. W.; Tham, F. S.; Siegrist, T.; Haddon, R. C. Synthesis, Structure and Physical Properties of the First OneDimensional Phenalenyl-Based Neutral Radical Molecular Conductor, J. Am. Chem.

Soc., 2004, 126, 1478-1484.


66

Page 67 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[98] Beer, L.; Brusso, J. L.; Cordes, A. W.; Godde, E.; Haddon, R. C.; Itkis, M. E.; Oakley, R. T.; Reed, R. W. Structure–property trends in π-stacked dithiazolo-dithiazolyl conductors, Chem. Commun, 2002, 2562-2563.

[99] Leitch, A. A.; Brusso, J. L.; Cvrkalj, K.; Reed, R. W.; Robertson, C. M.; Dube, P. A.; Oakley, R. T. Spin-canting in heavy atom heterocyclic radicals, Chem. Commun., 2007, 3368-3370.

[100] Rosokha, S. V.; Lu, J.; Han, B.; Kochi, J. K. Unusual structural effects of intermolecular π-bonding in the tetracyanopyrazine (ion-radical) dimer, New J. Chem. 2009, 33, 545-553.

[101] Casado, J.; Burrezo, P. M.; Ramírez, F. J.; López Navarrete, J. T.; Lapidus, S. H.; Stephens, P. W.; Vo, P. W.; Miller, J. S.; Mota, F.; Novoa, J. J. Evidence for Multicenter Bonding in Dianionic Tetracyanoethylene Dimers by Raman Spectroscopy, Angew.

Chem. Int. Ed. 2013, 52, 6421-6425.

[102] Cui, Z.-H.; Lischka, H.; Mueller, T.; Plasser, F.; Kertesz, M. Study of the Diradicaloid Character in a Prototypical Pancake‐Bonded Dimer: The Stacked


67


Page 68 of 97

Tetracyanoethylene (TCNE) Anion Dimer and the Neutral K2TCNE2 Complex,

ChemPhysChem, 2014, 15, 165-176.

[103] Novoa, J. J.; Miller, J. S. Four-Center Carbon-Carbon Bonding, Acc. Chem. Res. 2007, 40, 189-196.

[104] Molčanov, K.; Kojić-Prodić, B.; Babić, D.; Pajić. D.; Novosel, N.; Zadro, K. Temperature induced reversible structural and magnetic phase transitions in a crystal of tetrachlorosemiquinone anion radical, CrystEngComm, 2012, 14, 7958-7964.

[105] Torrey, H. A.; Hunter, W. H. The action of iodides on bromanil. Iodanil and some of its derivatives, J. Am. Chem. Soc., 1912, 34, 702-716.

[106] Molčanov, K.; Kojić-Prodić, B.; Babić, D.; Žilić, D.; Rakvin, B. Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals, CrystEngComm, 2011, 13, 5170-5178.

[107] Molčanov, K.; Kojić-Prodić, B. Spin pairing, electrostatic and dipolar interactions shape stacking of radical anions in alkali salts of 4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2dicarbonitrile (DDQ), CrystEngComm, 2017, 19, 1801-1808.


68

Page 69 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[108] Molčanov, K.; Stalke, D.; Šantić, A.; Demeshko, S.; Stilinović, V.; Mou, Z.; Kertesz, M.; Kojić-Prodić, B. Probing semiconductivity in crystals of stable semiquinone radicals: organic salts of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radical anion, CrystEngComm, 2018, 20, 1862-1873.

[109] Molčanov, K.; Babić, D.; Kojić-Prodić, B.; Stare, J.; Maltar-Strmečki, N.; Androš, L. Spin-coupling in dimer of 2,3-dicyano-5,6-dichlorosemiquinone radical anions characterised by ring separation distance of 2.81 Å, Acta Crystallogr. B, 2014, B70, 181190.

[110] Marzotto, A.; Clemente, D. A.; Pasimeni, L. Molecular structure of tetrapropylammonium-2,3-dichloro-5,6-dicyano-p-benzoquinone compared toM+ TCNQ− (M+=Rb+, K+, Cs+, or organic cations; TCNQ−=tetracyanoquinomethane) charge-transfer complexes, J. Cryst. Spectr. Res., 1988, 18, 545-554.

[111] Kazheva, O. N.; Ziolkovskiy, D. V.; Alexandrov, G. G.; Cheklov, A. N.; Dyachenko, O. A.; Starodub, V. A.; Khotkevich, A. V. Crystal and molecular structure of the new anion-


69


Page 70 of 97

radical salts—(N-Me-2-NH2-Pz)(TCNQ)2 and (N-Me-Tetra-Me-Pz)(TCNQ)2 (Pz is pyrazine), Synth. Met., 2006, 156, 1010-1016.

[112] Garcia-Yoldi, I.; Miller, J. S.; Novoa, J. J. Theoretical Study of the Electronic Structure of [Tetrathiafulvalene]22+ Dimers and Their Long, Intradimer Multicenter Bonding in Solution and the Solid State, J. Phys. Chem. A, 2009, 113, 7124-7132.

[113] Zanotti, G.; Del Pra, A. Structure of the potassium salt of p-chloranil, solvated with acetone, Acta Crystallogr. B, 1980, B36, 313-316.

[114] Molčanov, K.; Milašinović, V.; Ivić, N.; Stilinović, V.; Kolarić, D.; Kojić-Prodić, B.

Influence of cations on π-stacking of semiquinone radical anions, submitted to CrystEngComm.

[115] Oison, V.; Katan, C.; Rabiller, P.; Souhassou, M.; Koenig, C. Neutral-ionic phase transition: A thorough ab initio study of TTF-CA, Phys. Rev. B, 2003, 67, 035120.


70

Page 71 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[116] García, P.; Dahaoui, S.; Fertey, P.; Wenger, E.; Lecomte, C. Crystallographic investigation of temperature-induced phase transition of the tetrathiafulvalene-pbromanil, TTF-BA charge transfer complex, Phys. Rev. B, 2005, 72, 104115.

[117] García, P.; Dahaoui, S.; Katan, C.; Souhassou, M.; Lecomte, C. On the accurate estimation of intermolecular interactions and charge transfer: the case of TTF-CA ,

Faraday Discuss., 2007, 135, 217-235.

[118] Mayerle, J. J.; Torrance, J. B.; Crowley, J. I. Mixed-stack complexes of tetrathiafulvalene. The structures of the charge-transfer complexes of TTF with chloranil and fluoranil, Acta Cryst. B, 1979, B35, 2988-2995.

[119] Coppens, P. Direct Evaluation of the Charge Transfer in the TetrathiafulvaleneTetracyanoquinodimethane (TTF-TCNQ) Complex at 100°K by Numerical Integration of X-Ray Diffraction Amplitudes, Phys. Rev. Lett. 1975, 35, 98-100.

[120] Huang, T. Z.; Taylor, R. P.; Soos, Z. G. Electron Dipolar Linewidth of SingleCrystal TMPD Chloranil, Phys. Rev. Lett. 1972, 28, 1054-1057.


71


Page 72 of 97

[121] Dressel, M.; Peterseim, T. Infrared Investigations of the Neutral-Ionic Phase Transition

in

TTF-CA

and

Its

Dynamics,

Crystals,

2017,

7,

17.

DOI:10.3390/cryst7010017.

[122] Katan, C.; Koenig, C. J. Phys. Condens. Matter, 1999, 11, 4163-4177.

[123] Sun, D.; Rosokha, S. V.; Kochi, J. K. Reversible Interchange of Charge-Transfer versus Electron-Transfer States in Organic Electron Transfer via Cross-Exchanges between Diamagnetic (Donor/Acceptor) Dyads, J. Phys. Chem. B, 2007, 111, 6655-6666.

[124] Zaman, Md. B.; Morita, Y.; Toyoda, J.; Yamochi, H.; Saito, G.; Yoneyama, N.; Enoki, T.; Nakasuji, K. Charge-Transfer Complex of a New Acceptor Cyananilate with Tetramethyltetrathiafulvalene, (TMTTF)2HCNAL, Chem. Lett. 1997, 729-730.

[125] Lapidus, S. H.; Naik, A.; Wikstrom, A.; Massa, N. E.; Phouc, V. T.; del Campo, L.; Lebegue, S.; Angyan, J. G.; Abdel-Fattah, T.; Pagola, S. The Black Polymorph of TTFCA: TTF Polymorphism and Solvent Effects in Mechanochemical and Vapor Digestion Syntheses, FT-IR, Crystal Packing, and Electronic Structure, Cryst. Growth Des. 2014,

14, 91-100.


72

Page 73 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[126] Lieffrig, J.; Jeannin, O.; Shin, K.-S.; Auban-Senzier, P.; Formigue, M. Halogen Bonding Interactions in DDQ Charge Transfer Salts with Iodinated TTFs, Crystals, 2012,

2, 327-337.

[127] García-Orduña, P.; Dahaoui, S.; Lecomte, C. Intermolecular interactions and charge transfer in the 2:1 tetrathiafulvalene bromanil complex, (TTF)2-BA, Acta Cryst. B, 2011, B67, 244-249.

[128] Murata, T.; Morita, Y.; Yakiyama, Y.; Fukui, K.; Yamochi, H.; Saito, G.; Nakasuji, K. Hydrogen-Bond Interaction in Organic Conductors: Redox Activation, Molecular Recognition, Structural Regulation, and Proton Transfer in Donor−Acceptor ChargeTransfer Complexes of TTF-Imidazole, J. Am. Chem. Soc., 2007, 129, 10837-10846.

[129] Becker, J. Y.; Bernstein, J.; Bittner, S.; Shaik, S. S. New 'Te-TTF' dimers, arylsubstituted TCNQ and quinone derivatives: synthesis, electrochemistry and molecular structure, Pure Appl. Chem. 1990, 62, 467-472.

[130] Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π interaction: evidence, nature and

consequences, Wiley-VCH, 1998.


73


Page 74 of 97

[131] Quiñonero, D.; Frontera, A.; Garau, C.; Ballester, P.; Costa, A.; Deyà, P. M. Interplay Between Cation–π, Anion–π and π–π Interactions, ChemPhysChem, 2006, 7, 2487-2491.

[132] Newberry, R.W.; Raines, R. T. The n→π* Interaction, Acc. Chem. Res. 2017, 50, 1838-1846.

[133] Molčanov, K.; Mali, G.; Grdadolnik, J.; Stare, J.; Stilinović, V.; Kojić-Prodić, B. Iodide∙∙∙π interactions of perhalogenated quinoid rings in co-crystals with organic bases,

Cryst. Growth Des. 2018, 18, 5182-5193.

[134] Kojić-Prodić, B.; Molčanov, K. The Nature of Hydrogen Bond: New Insights into Old Theories, Acta Chim. Slov., 2008, 55, 692-708.

[135] Eraković, M.; Cinčić, D; Molčanov K; Stilinović, V., Crystallographic Charge Density Study of the Partial Covalent Nature of Strong N∙∙∙Br Halogen Bonds, manusctipt in preparation.


74

Page 75 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[136]

Saenger,

W.;

Betzel,

C.;

Hingerty,

B.;

Brown,

G.

M.

Flip‐Flop‐Wasserstoffbrückenbindungen in β‐Cyclodextrin — ein allgemein gültiges Prinzip in Polysacchariden?, Angew. Chem., 1983, 95, 908-909.

[137] Steiner, T.; Saenger, W. Geometry of carbon···oxygen hydrogen bonds in carbohydrate crystal structures. Analysis of neutron diffraction data, J. Am. Chem. Soc. 1992, 114, 10146-10154.

[138] Ohno, K.; Okimura, M.; Akai, N.; Katsumoto, Y. The effect of cooperative hydrogen bonding on the OH stretching-band shift for water clusters studied by matrix-isolation infrared spectroscopy and density functional theory , Phys. Chem. Chem. Phys., 2005, 7, 3005-3014.

[139] Winter, S. M.; Cvrkalj, K.; Dube, P. A.; Robertson, C. M.; Probert, M.R.; Howard, J. A. K.; Oakley, R. T. Metamagnetism in a π-stacked bis-dithiazolyl radical, Chem.

Commun. 2009, 7306−7308.

[140] Molčanov, K.; Jelsch, C.; Wenger, E.; Stare, J.; Madsen, A. Ø.; Kojić-Prodić, B. Experimental evidence of 3-centre, 2-electron covalent bond character of the central O-


75


Page 76 of 97

H-O fragment on the Zundel cation in crystals of Zundel nitranilate tetrahydrate,

CrystEngComm, 2017, 19, 3898-3901.

[141] Hakkert, S. B.; Erdélyi, M. Halogen bond symmetry: the N–X–N bond, J. Phys.

Org. Chem., 2014, 28, 226-233.

[142] Oliveira, V.; Kraka, E., Cremer, D. The intrinsic strength of the halogen bond: electrostatic and covalent contributions described by coupled cluster theory, Phys. Chem.

Chem. Phys. 2016, 18, 33031-33046.

[143] Robinson, S. W.; Mustoe, C. L.; White, N. G.; Brown, A.; Thompson, A. L.; Kennepohl, P.; Beer, P. D. Evidence for Halogen Bond Covalency in Acyclic and Interlocked Halogen-Bonding Receptor Anion Recognition, J. Am. Chem. Soc., 2015,

137, 499-507.

[144] Dunitz, J. D. Intermolecular atom-atom bonds in crystals? IUCrJ, 2015, 2, 157158.


76

Page 77 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[145] Lecomte, C.; Espinosa, E.; Matta, C. On atom–atom `short contact' bonding interactions in crystals, IUCrJ, 2015, 2, 161-163.

[146] Taylor, R.; Kennard, O. Crystallographic evidence for the existence of CH···O, CH···N and CH···Cl hydrogen bonds, J. Am. Chem. Soc., 1982, 104, 5063-5070.

[147] Banerjee, R.; Desiraju, G. R. Crystal Engineering: A Brief Overview, J. Chem. Sci., 2010, 122, 667-675.

[148] Gilli, G.; Gilli, P. The Nature of the Hydrogen Bond, Oxford University Press, Oxford, 2013.

[149] Gilli, P.; Gilli, G. Hydrogen bond models and theories: The dual hydrogen bond model and its consequences, J. Mol. Struct. 2010, 972, 2-10.

[150] Wilson, C. C.; Goeta, A. Towards Designing Proton‐Transfer Systems—Direct Imaging of Proton Disorder in a Hydrogen‐Bonded Carboxylic Acid Dimer by Variable‐Temperature X‐ray Diffraction, Angew. Chem., Int. Ed. 2004, 43, 2095-2099.


77


Page 78 of 97

[151] Parkin, A.; Harte, S. M.; Goeta, A.; Wilson, C. C. Imaging proton migration from X-rays and neutrons, New J. Chem. 2004, 28, 718-721.

[152] Biliškov, N.; Kojić-Prodić, B.; Mali, G.; Molčanov, K.; Stare, J. J. A partial proton transfer in hydrogen bond O–H∙∙∙O in crystals of anhydrous potassium and rubidium complex chloranilates, Phys. Chem. A, 2011, 115, 3154-3166.

[153] Molčanov, K.; Stare, J.; Vener, M. V.; Kojić-Prodić, B.; Mali, G.; Grdadolnik, J.; Mohaček Grošev, V. Nitranilic acid hexahydrate, a novel benchmark system of the Zundel cation in an intrinsically asymmetric environment: spectroscopic features and hydrogen bond dynamics characterised by experimental and theoretical methods, Phys. Chem.

Chem. Phys. 2014, 16, 998-1007.

[154] Bernal, I. The composition, charge and architecture of hydronium ions as observed in the crystalline state, C. R. Chimie, 2006, 9, 1454-1466.

[155] Cavallo, G.; Murray, J. S.; Politzer, P.; Pilati, T.; Ursini, M.; Resnati, G. Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts, IUCrJ, 2017, 4, 411-419.


78

Page 79 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[156] Androš Dubraja, L.; Molčanov, K.; Žilić, D.; Kojić-Prodić, B.; Wenger, E. Multifunctionality and size of the chloranilate ligand define the topology of transition metal coordination polymers, New J. Chem., 2017, 41, 6785-6794.

Insert Table of Contents Graphic and Synopsis Here

Crystal packing interactions contributing to stacking arrangements of aromatic and nonaromatic systems are reviewed and discussed. π-interactions cover a broad range of energies, ranging from ≤ 1 kcal mol-1 to ≥ 20 kcal mol-1, and the interactions span from weak dispersion to multicentric covalent bonding. Thus, stacking is similar to hydrogen


79


Page 80 of 97

bonding, which also ranges between dispersion and two-electron/three-centric covalent bonding.


80

Page 81 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphical abstract 395x299mm (72 x 72 DPI)



Scheme 1 314x223mm (95 x 95 DPI)


Page 82 of 97

Page 83 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60







Page 84 of 97

Page 85 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1 383x158mm (96 x 96 DPI)



Figure 2 1002x268mm (96 x 96 DPI)


Page 86 of 97

Page 87 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60







Page 88 of 97

Page 89 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60







Page 90 of 97

Page 91 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60







Page 92 of 97

Page 93 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60





Figure 10 270x385mm (72 x 72 DPI)


Page 94 of 97

Page 95 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 11 846x260mm (72 x 72 DPI)



Figure 12 632x342mm (72 x 72 DPI)


Page 96 of 97

Page 97 of 97 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13 376x257mm (96 x 96 DPI)


from non-covalent to covalent multicentric bonding - ACS Publications

Recommend Documents