CATION–P INTERACTION IS AN EXAMPLE OF NON-COVALENT BONDING BETWEEN A MONOPOLE (CATION) AND A QUADRUPLE (Π SYSTEM). THE CATION–P INTERACTION PLAYS AN IMPORTANT ROLE IN NATURE, PARTICULARLY IN IN PROTEIN STRUCTURES AND MOLECULAR STRUCTURE RECOGNITION [1]. IN THE PRESENT STUDY, WE WISH TO INVESTIGATE THE ELECTRONIC STRUCTURE AND BOND NATURE OF CATION–P INTERACTION BETWEEN AROMATIC BENZENE AND LI+ WITH THE THEORIES OF ATOMS IN MOLECULES (AIM) AND NATURAL BOND ORBITALS (NBO)...

BACKGROUND: CATION-P AND ANION-P INTERACTIONS REFER TO THE NONCOVALENT ATTRACTION BETWEEN THE CATION AND ANION WITH A P MOLECULE. NUMEROUS EXPERIMENTAL AND THEORETICAL WORKS SHOWS THAT THESE INTERACTIONS PLAY A PROMINENT ROLE IN SEVERAL AREAS OF CHEMISTRY AND BIOLOGY [1, 2]. IN THIS WORK, THE ROLE OF CATION-P AND ANION-P INTERACTIONS ON THE NATURE OF BORAZINE BONDS IS INVESTIGATED. CATION-P AND ANION-P INTERACTIONS HAVE BEEN STUDIED IN MODELING BY LI+, NA+, K+, F-, CL- AND BR- IONS AND BORAZINE AS Π-SYSTEM.METHODS: THE GEOMETRIES WERE OPTIMIZED WITH BSSE CORRECTION AT THE MP2/6-311++G (D, P) LEVEL USING GAUSSIAN09 PROGRAM. THE AIM AND NRT ANALYSES WERE PERFORMED AT THE SAME LEVEL USING AIM2000 AND NBO3.1 PROGRAMS.RESULTS: THE ION-P COMPLEXES OF BORAZINE ARE FOUND TO BE NOT PLANER. DUO TO FORMATION OF CATIONIC COMPLEXES, THE N-H/B-H BOND LENGTHS INCREASE/DECREASE. A REVERSE BEHAVIOR IS FOUND FOR ANIONIC ONES. THE B-NBONDS IN THE CATIONIC COMPLEXES ARE SLIGHTLY LONGER THAN THE FREE BORAZINE, WHILE THE CHANGES OF THESE BONDS ARE NEGLIGIBLE IN THE PRESENCE OF ANION-P. THE COMPLEXATION ENERGY VALUES ARE FOUND TO BE MORE NEGATIVE FOR CATIONIC COMPLEXES THAN THE ANIONIC SYSTEMS. THE AIM ANALYSIS INDICATES THE COVALENT NATURE OF N-H AND B-H BONDS AND THE PARTIALLY COVALENT NATURE OF B-N BOND. THE ION-P INTERACTIONS LEAD TO INCREMENT IN IONIC CHARACTER AND REDUCTION IN COVALENT CHARACTER OF B-N BOND. A DIRECT RELATIONSHIP IS FOUND BETWEEN THE COVALENT CHARACTER OF B-N BOND AND ION SIZE. THE COVALENT CHARACTER OF H-N BOND IS DIMINISHED/AMPLIFIED BY CATION-P/ANION-P INTERACTIONS. ALTHOUGH THE IONIC CHARACTER OF B-H BOND INCREASES BY ANION-P INTERACTIONS, THE COVALENT CHARACTER OF THIS BOND DECREASES. THIS BEHAVIOR IS REVERSED IN THE CATION-P COMPLEXATION.CONCLUSION: A STRONGER ION-P INTERACTION IS OBSERVED FOR THE BORAZINE RING WITH THE GREATER LOSS IN PLANARITY. A REVERSE RELATIONSHIP IS FOUND BETWEEN DECOMP AND DION-P. DUO TO ION-P INTERACTIONS, THE COVALENT/IONIC CHARACTERS OF B-N BOND DECREASE/INCREASE RESPECTIVELY.

BACKGROUND: ALTHOUGH MOST OF THE EXPERIMENTAL AND THEORETICAL WORKS ON CATION-P AND ANION-P INTERACTIONS HAS BEEN DONE ABOUT INTERACTIONS OF IONS WITH AROMATIC SYSTEMS [1, 2], THE ION-P INTERACTIONS ARE NOT LIMITED TO AROMATIC RINGS; OTHER P SYSTEMS SUCH AS ISOLATED DOUBLE AND TRIPLE BONDS CAN ALSO INTERACT WITH IONS [3]. IN THE PRESENT LETTER, THE NATURE OF CATION-P AND ANION-P INTERACTIONS HAVE BEEN EXAMINED IN IONIC COMPLEXES OF ETHYLENE, (E) -1, 2-DIFLUOROETHYLENE AND TETRAFLUOROETHYLENE.METHODS: THE GEOMETRIES HAVE BEEN OPTIMIZED AT MP2/6-311++G (D, P) LEVEL OF THEORY USING GAUSSIAN 09 SUITE OF PROGRAMS. BASIS SET SUPERPOSITION ERROR (BSSE) HAS BEEN CONSIDERED BY THE COUNTERPOISE (CP) METHOD IN THE GEOMETRY OPTIMIZATION. THE POPULATION ANALYSIS HAS ALSO BEEN PERFORMED USING AIM2000 AND NBO3.1 PROGRAMS.RESULTS: THE RESULTS INDICATE THAT THE DEPENDENCE BETWEEN COMPLEXATION ENERGY (DE) AND DION–P SHOULD SEPARATELY BE CONSIDERED FOR EACH ION GROUP (ALKALI, ALKALINE-EARTH OR HALOGEN). THE DION–P DECREASES WITH THE INCREASING  |DE| VALUE. THE VALUE OF ELECTRON DENSITY AT THE ION…C=C BOND CRITICAL POINT (RBCP) WAS EVALUATED. THE NBO CALCULATIONS SHOW THAT THE MOST IMPORTANT DONOR–ACCEPTOR INTERACTIONS ARE PC-C ® LP* CATION AND LPANION→ P* C-C FOR CATION-P AND ANION-P, RESPECTIVELY. THE ORDER OF ENERGY VALUES (E2) IN THESE INTERACTIONS IS SIMILAR TO |ΔE| AND RBCP. ALSO, THE CHARACTERISTICS OF C=C BOND CHANGES IN THE PRESENCE OF ION– P INTERACTIONS. FOR CATION–P INTERACTIONS, A DIRECT RELATIONSHIP IS OBSERVED BETWEEN C=C BOND LENGTH AND |DE|, RBCP AND E2 VALUES. THE C=C BOND IS MOSTLY COVALENT IN CHARACTER WITH PARTLY IONIC CHARACTER TOO. IT IS OBTAINED FROM NRT CALCULATIONS THAT THE BOND ORDER OF C=C IS DIMINISHED BY CATIONS. THE DECREASE IN C=C BOND ORDER IS DUE TO THE REDUCTION OF COVALENT CHARACTER OF BOND. THESE BEHAVIORS ARE REVERSED IN THE PRESENCE OF ANION-P. ALSO, THE IONIC CHARACTER OF C=C BOND INCREASES BY BOTH ION-P INTERACTIONS.CONCLUSION: IN THIS WORK, THE MEANINGFUL RELATIONSHIPS HAVE BEEN OBTAINED BETWEEN |DE|, RBCP AND E2 VALUES AND THE NATURE OF C=C BOND.

THE NATURE OF THE COMPLEXES OF CATION NA+WITH DIFFERENT P-SYSTEMSSUCH AS PARA-SUBSTITUTED (R= CL AND NH2) BENZENE DERIVATIVES HAVE BEEN INVESTIGATED BY UB3LYP METHOD USING 6-311++G** BASIS SET. THE NATURAL BOND ORBITAL (NBO) ANALYSIS AND THE BADER’S QUANTUM THEORY OF ATOMS IN MOLECULES (AIMS) WERE USED TO ELUCIDATE THE INTERACTION CHARACTERISTICS OF THESE COMPLEXES.FURTHERMORE, THE EFFECTS OF INTERACTIONS ON SOME NMR DATA ARE ALSO EVALUATED.

FOR SEVERAL YEARS, IT HAS BEEN WIDELY RECOGNIZED THAT NONCOVALENT INTERACTIONS ARE OF PIVOTAL IMPORTANCE IN MANY FIELDS OF BIOLOGY, CHEMISTRY, AND MATERIALS SCIENCE. IN PARTICULAR, THE INTERMOLECULAR INTERACTIONS INVOLVING AROMATIC SYSTEMS, COMMONLY CALLED P–P INTERACTIONS, PLAY A CRUCIAL ROLE IN THE INTERCALATION OF CERTAIN DRUG MOLECULES INTO DNA, …

THE P–P STACKING INTERACTIONS ARE WEAK NONCOVALENT FORCES THAT PLAY AN ESSENTIAL ROLE IN SUPRAMOLECULAR CHEMISTRY, DRUG DESIGN, BIOCHEMISTRY, CRYSTAL ENGINEERING AND MOLECULAR SCIENCE [1]...