Screening polymorphism in a Ni(ii) metal–organic framework: experimental observations, Hirshfeld surface analyses and DFT studies

Abstract

A new polymorph of a 1D Ni(II) polymer with iminodiacetic acid (IDA), namely diaquaiminodiacetatonickel(II) [Ni(C₄H₅NO₄)(H₂O)₂]_n, is discovered one decade after the X-ray characterization of the other polymeric polymorph. The new polymorph (named form-II) is characterized by single-crystal X-ray diffraction, and its structural comparison with the previous polymorph (named form-I) is reported. The new form-II (space group Pbca) not only is a conformational polymorph, but it also exhibits packing polymorphism with the already known P2₁ca crystal form of the polymer. The intermolecular interactions generate distinct packing features in the two forms. The present study reports a detailed analysis of Hirshfeld surfaces and fingerprint plots, facilitating a comparison of intermolecular interactions in the supramolecular architectures. Moreover, the differences in the H-bonding networks of the polymorphs have been analysed using a combination of density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations.