Phenomenal Observation of Attractive Intermolecular CH⋯HC Interaction in a Mercury (II) Complex: An Experimental and First‐Principles Study

The nature of the attractive intermolecular C@H…H@C interaction, which could affect the crystal packing and solid-state molecular structure, is yet unknown. Here, a novel mercury (II) complex including N-(2-biphenyl)pyrazine-2-carboxamide ligand, one such system, has been synthesized and characterized by a single crystal X-ray diffraction. The existence of attractive intermolecular C@H⋯H@C interaction (-2.64 to @9.30 kj/mol depending on computational levels) is a notable feature in the crystal packing of this complex, which is the first observation of intermolecular C@H⋯H@C interaction in a metal complex. From crystallographic data, this contact has a distance of 2.172 Å which is 9.5% shorter than the sum of the van der Waals radii of two hydrogen atoms, which is the primary condition of having intermolecular interactions. We study the nature C@H…H@C interaction in the synthesized mercury (II) complex using periodic/non-periodic density functional theory in conjunction with quantum theory of atoms in molecules, non-covalent interaction reduced density gradient method, natural bond orbital, and energy decomposition analysis tools. Our results suggest that C@H⋯H@C interaction has closed-shell, donoracceptor, and van der Waals nature.