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PCCP Accepted Manuscript This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/pccp Page 1 of 14Journal Name Physical Chemistry Chemical Physics Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx ARTICLE TYPE Intermolecular X…X (X = C, N and O) Dipole Interaction between Atoms in Similar Chemical Environment Karunakaran Remya and Cherumuttathu H. Suresh* Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX 5 DOI: 10.1039/b000000x Manuscript Clear evidence for intermolecular carbon-carbon (C…C), nitrogen-nitrogen (N…N) and oxygen-oxygen (O…O) interactions between atoms in similar chemical environment in homogeneous dimers of organic molecules are obtained from molecular orbital (MO), natural bond orbital (NBO) and atoms-in-molecule (AIM) electron density analyses at M06L/6-311++G(d,p) level of DFT. These X…X type interactions are 10 mainly due to local polarization effects, causing segregation of electron rich and electron deficient regions in X atoms, leading to complementary electrostatic interactions between them. NBO analysis provides evidence for charge transfer between the two X atoms. Even for symmetrical molecules such as acetylene, induced dipoles in the dimer creates C…C bonding interaction. The strength of this type of interaction Accepted increases with increase in the dipole moment of the molecule. The energy decomposition analysis (EDA) 15 shows that electrostatic component of the interaction energy (Eint) is very high (up to 95.86%). C…C interaction between similar carbon atoms are located in several crystal structures reported in the literature. Further, the MO, AIM and electrostatic potential analysis support O…O and N…N interaction between similar atoms in many molecular dimers. A good prediction of Eint is achieved in terms of total gain in electron density at the non-covalently interacting intermolecular bonds (∑ρ) and monomer dipole moment 20 (µ). A rigorously tested QSAR equation is derived to predict Eint for all dimer systems (Eint (kcal/mol) = - Physics 138.395∑ρ (au) – 0.551µ (Debye)). This equation suggests that polarization induced bonding interaction between atoms in similar chemical environment could be a general phenomenon in chemistry. The results are further validated using different density functionals and G3MP2 method. Dedicated to Professor Shridhar R. Gadre on the occasion of his 65th birthday. 45 of ‘dicarbon bond’ (similar to dihydrogen bond) between a donor 25 Introduction and an acceptor carbon atom in complexes of CO with CH3-X is Chemical described by Varadwaj et al28. Development of new theoretical as well as experimental A previous study by us on the cooperative clustering of techniques has led to better understanding of non-covalent acetonitrile33 showed that the patterns with maximum number of interactions. This led to the discovery of several new types of 50 antiparallel orientations own maximum stability and inter molecular interactions involving halogens1-8, chalcogens9-14 15-16 cooperativity. The atoms-in-molecules (AIM) analysis showed 30 and pnicogens. Non covalent interactions involving group IV 17-28 bond critical points (BCPs) and bond paths between the nitrile elements have recently gained interest . The non covalent carbon atoms of two acetonitrile molecules with antiparallel interaction of a covalently bonded group IV element with an orientations along with hydrogen bonding interactions. These electron donor site has been grouped as a σ hole4, 29 bonding 55 intermolecular C…C interactions were unusual, since they were interaction along with halogen, chalcogen and pnicogen bonds by Chemistry 8, 30-32 observed between carbon atoms of similar chemical environment. 35 Politzer et al . After that, a detailed study on the interaction The studies reported in literature so far deal with donor-acceptor of σ hole of F3MX (M = C, Si, Ge and X = F, Cl, Br, I) with the 18 type interactions where donor and acceptor atoms belong to lone pair on nitrogen of HCN is published by Bundhun et al . different chemical environments. This led us to the search for The term ‘carbon bond’ for the interaction of electron deficient 60 intermolecular interaction between atoms in similar chemical carbon with electron rich centers of molecules like H2O and H2S 19 environments in molecules with different functional groups. 40 is introduced by Arunan and Mani . They predicted the ‘carbon In this paper, dimers of several organic molecules with different bond’ to be important in hydrophobic interactions as well as in 17 functionalities, rich in multiple bonds, and most of them with an the stabilization of intermediate of SN2 reaction. Bauzá et al inherent dipole moment are studied for intermolecular C…C Physical coined the term ‘tetrel bonding’ for describing the interaction of 65 interaction between carbon atoms in similar chemical heavier group IV elements with nucleophilic centres. The concept environment. Evidence for such C…C interactions is shown This journal is © The Royal Society of Chemistry [year] [journal], [year], [vol], 00–00 | 1 Physical Chemistry Chemical Physics Page 2 of 14 using AIM and molecular orbital (MO) analyses. Strong evidence organic compounds from literature. We have also shown for such interactions is given in crystal structures of several intermolecular N…N and O…O interactions between nitrogen Manuscript 5 Accepted Figure 1. Dimers showing C…C interactions (dotted lines) between carbon atoms in similar chemical environment. Distances are given in Å. Interactions other than C…C type are not marked in the figure for simplicity Physics Chemical Chemistry 10 Figure 2. AIM plots of the dimers showing C…C interaction between similar carbon atoms. The ρ values at the bond critical point are given in au. Color code for atoms: dark blue, carbon; light blue, nitrogen; light green, fluorine; yellow, sulfur; pink, chlorine; brown, bromine; ash, hydrogen and oxygen atoms of similar chemical environments. Intermolecular chalcogen…chalcogen interactions are previously Computational Methods Physical 13, 34 described in literature as leading to the formation of tubular 37 12, 35 36 All the molecules are optimized using M06L density functional 15 structures and crystals . 2 | Journal Name, [year], [vol], 00–00 This journal is © The Royal Society of Chemistry [year] Page 3 of 14 Physical Chemistry Chemical Physics theory. The basis set used is 6-311++g(d,p). This model analyzed. This results in the departure from the idealized Lewis chemistry was previously shown to be suitable in calculating both structure description. For each pair of donor (i) and acceptor (j) geometry and interaction energy of non-covalently bound dimers NBOs, the stabilization energy E2 associated with i → j in an extensive benchmark study38 carried out by us. All the delocalization is calculated as 5 dimers are confirmed to be minima by calculating the frequency. 2 The calculations are done using Gaussian0939 suite of programs. F(i, j) 60 E2 = DEij = qi (2) Interaction energy (Eint) is calculated by subtracting twice the ej- ei energy of the constituent monomer from the energy of a dimer. The monomers are also optimized at the same level. Counterpoise where qi is the donor orbital occupancy, εi, εj are diagonal 40 10 correction is done using Boys and Bernardi method as elements (orbital energies) and F(i,j) is the off-diagonal NBO implemented in Gaussian09. Further validation of the results is Fock matrix element. done using B3LYP, CAM-B3LYP41 - the long range corrected version of B3LYP42 - and B97143 functionals. To assess the effect Results and Discussion of dispersion, B3LYP-D3 method is also employed which uses Manuscript 65 Intermolecular C…C interaction between carbon atoms in 15 Grimme’s dispersion correction along with Becke-Johnson similar chemical environment damping function44. The basis set used for all these calculations is 6-311++g(d,p). Further, the high accuracy G3MP245 method is used to get accurate binding energy values for the dimers. 46 Atoms-in-molecule (AIM) analysis considers the distribution 20 of electronic charge of atoms in the field of nuclei and its interference with external fields. In this method, critical points in topology of the charge density are related to physical information like bonds. The programs used are AIM200047-49 and AIMALL50. Accepted AIMALL generated molecular graphs are used in the manuscript 25 for illustrating the bonding interactions. MO analysis was done to confirm the bonding interactions corresponding to the intermolecular bond critical points shown by the AIM analysis. Molecular electrostatic potential (MESP), defined by equation (1) can be used as a tool for understanding intermolecular 51-54 30 interactions . It directly reflects the charge distribution in the Physics system, based upon Coulomb’s law55. The molecular electrostatic potential at a point r, V(r) is given as, N Z ρ(r¢)d 3r¢ V (r) = å A - ò (1) A r - R A r - r¢ where ZA is the nuclear charge and RA is the radius of nucleus A 35 and ρ(r') is the electron density.
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