FULL PAPER DOI:10.1002/ejic.201500030 Hydrogen Bond, π–π, and CH–π Interactions Governing the Supramolecular Assembly of Some Hydrazone Ligands and Their Mn II Complexes – Structural and Theoretical Interpretation Dipali Sadhukhan, [a,b] Monami Maiti, [a] Guillaume Pilet,* [b] Antonio Bauzá, [c] Antonio Frontera, [c] and Samiran Mitra* [a] Keywords: Hydrazone ligands / Manganese / Structure elucidation / Noncovalent interactions / Supramolecular energy calculations The hydrazone Schiff base ligands (E)-N'-(2-hydroxybenzyl- idene)acetohydrazide (HL 1 ) and (E)-N'-(2,3-dihydroxy- benzylidene)acetohydrazide (H 2 L 2 ) with a functional group variation in the aromatic moiety have been synthesized. The ligands have been used to synthesize the following Mn II complexes: the mononuclear complex [Mn(HL 1 ) 2 ]- [ClO 4 ] 2 ·2H 2 O(1), the cocrystallized discrete dinuclear com- plex {[Mn(HL 1 ) 2 ]·[Mn(L 1 ) 2 ]}[ClO 4 ] 2 (2), and the phenoxido- bridged dinuclear complex [Mn(μ-HL 2 )(H 2 O)] 2 [ClO 4 ] 2 (3). The ligands and the complexes were characterized by FTIR Introduction Supramolecular chemistry deals with weak and reversible noncovalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydro- phobic forces, van der Waals forces, π–π interactions, CH–π interactions, electrostatic effects, and so on. Supramolecular interactions are demonstrated in molecular self-assembly, peptide folding, molecular recognition, host–guest chemis- try, and mechanically interlocked molecular architectures. [1] Among these weak forces, hydrogen bonding has a signifi- cant role in molecular packing for the development of various architectures through crystal engineering. [2] [a] Department of Chemistry, Jadavpur University, Raja S. C. Mullick Road, Kolkata 700032, India E-mail: smitra_2002@yahoo.com samiranju92@gmail.com http://www.jaduniv.edu.in/profile.php?uid=19 [b] Groupe de Cristallographie et Ingénierie Moléculaire, Laboratoire des Multimatériaux et Interfaces, UMR 5615 CNRS-Université Claude Bernard Lyon 1, Bât. Chevreul, 43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France E-mail: guillaume.pilet@univ-lyon1.fr www.guillaumepilet.sitew.fr [c] Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Balears), Spain Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201500030. Eur. J. Inorg. Chem. 2015, 1958–1972 © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1958 and UV/Vis spectroscopic techniques, and their crystal struc- tures were determined by single-crystal X-ray diffraction analysis. 1 H and 13 C NMR spectroscopy shows evidence of keto–enol tautomerism of the ligands in solution. All of the compounds develop hydrogen-bonded assemblies of dif- ferent dimensionalities and architectures. CH–π and π–π in- teractions also contribute significantly to the overall binding energies of the supramolecular assemblies. The supramolec- ular interaction energies have been computed at the BP86- D3/def2-TZVPD level of theory. Hydrogen bonding is the noncovalent interaction be- tween hard acids and hard bases and has a major contri- bution from electrostatic or Coulombic interactions. Ex- change repulsion, polarization energy, charge-transfer en- ergy, covalent bonding, and dispersion forces also contrib- ute to a different extent. [3] The energy of a hydrogen bond varies from 0.25 to 40 kcal/mol depending on the polarities of the donor and acceptor atoms. [4] As hydrogen bonds are polar, they are stable in apolar solvents in the absence of competitive hydrogen bonding with the solvent. In contrast to classical hydrogen-bonding interactions, CH–π interac- tions have been recognized to be the weakest nonclassical hydrogen bond [5] and contribute significantly in various fields of chemistry such as molecular conformations, [6] self- assembly, [7] chiral recognition, [8] and crystal packing. [9] CH–π interactions occur between soft acids and soft bases and largely comprise electron correlation energy or disper- sion energy. Electrostatic interactions also contribute to a minor extent (ca. 20 %). [10] CH–π interactions are much weaker than conventional H-bonding interactions. High- level ab initio calculations for a benzene–methane complex gave a value of –1.45kcal/mol for the interaction energy, which varies to –5.64 kcal/mol for a benzene–chloroform complex, as the C–H component is significantly activated by three electron-withdrawing groups. [11] Unlike conven- tional H bonding, CH–π interactions are orientation-inde- pendent and persist in highly polar media such as water;