Chlorine anion–π and π−–π− interactions in two tetrazolyl derivative based Cu2+ complexes and quantum chemical calculations

Two bis(tetrazolyl)amine (H2BTA) and 5,5′-azotetrazolate (AT) based Cu2+ supramolecular complexes [Cu(H2BTA)Cl2(H2O)]·2H2O (1) and [Cu2(AT)2(pn)3]·2H2O (2) (pn = 1,3-diaminopropane) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1, each Cu2+ ion displays a tetragonal pyramidal structure and an anion–π of Cl−–π interaction has been observed. The Cl−–π binding interaction together with O–H···Cl, N–H···Cl, N–H···O and O–H···N four hydrogen bonds link the complex units and lattice water molecules to form a 3D supramolecular network structure. In 2, the Cu2+ ions show an elongated octahedral structure and a 1D chain structure bridged by μ2-trans-AT2− ligands is found. An unusual face-to-face π−–π− stacking interaction between trans-AT2− anions in 2 is found. Complex 2 also exhibits a 3D supramolecular structure in which the π−–π− stacking, O–H···N and N–H···O hydrogen bonding and electrostatic interactions are responsible for the stabilization of the complex. The aqueous solution of 2 shows photochromic property. The Cl−–π and π−–π− interaction energies in 1 and 2 were calculated at MP2 level using gaussian 09 suite and demonstrated.