Spodium bonds and metal-halogen•••halogen-metal interactions in propagation of monomeric units to dimeric or polymeric architectures

In this work we report on crystal structures of a heteroleptic coordination polymer [Hg-2 (HL)Cl-4](n) (1) where the nitrogen atom of the peripheral pyridine fragment is linked to another HgCl2 molecule and two discrete mononuclear heteroleptic complexes [Hg(HL)I-2] (2) and [Mn(HL)Cl-2]center dot MeOH (3 center dot MeOH), which were obtained through self-assembling of N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) with HgCl2, HgI2 or MnCl2, respectively. HL coordinates the Hg-II salts in its keto-form, while MnCl2 is chelated by a zwitterionic form of HL confirmed by the solid state IR spectroscopy. The studied here ligand molecule has a tendency to involve the 4-pyridyl nitrogen atom in coordination bonding which is correlated with the ability to transfer the electric charge and production of a zwitterionic form. The crystal structure and Hirshfeld surface data analysis show a great importance of spodium bonds and metal-halogen center dot center dot center dot halogen-metal interactions. A prominent consequence of lack of sigma- or pi-hole interactions in case of MnII ion is the isolation of metal center from the external contacts. Apart form this in 3 center dot MeOH the halogen.halogen interactions are absent. It seems that the sigma- or pi-hole regions formed at the Hg-II cation in 1 and 2 favor the participation of coordinated Cl or I atoms in the M-Hal center dot center dot center dot Hal'-M' halogen center dot center dot center dot halogen interactions, whereas in complex 3 center dot MeOH there are no metal or halogen centered sigma-hole interactions. Thus, the 1D coordination polymer in 1 is stabilized by the Hg center dot center dot center dot Cl spodium bonding. Additionally, the observed intermolecular halogen center dot center dot center dot halogen interactions in 1 provide cross-linking of the 1D coordination polymers, yielding a 2D supramolecular double-layered sheet. In 2 an additional contact between halogen and mercury atoms results in a dimeric unit. These dimers are linked into a 1D polymer by halogen center dot center dot center dot halogen interactions between metal bounded iodine atoms. The DFT theoretical studies were applied to analyze the Hg center dot center dot center dot X non-covalent spodium interactions that govern the formation of the 1D polymeric structure in 1 and self-assembled dimers in 2. (C) 2021 Elsevier B.V. All rights reserved.