Metal-organic and supramolecular lead(II) networks assembled from isomeric nicotinoylhydrazone blocks: The effects of ligand geometry and counter-ion on topology and supramolecular assembly

Abstract

A new series of six structurally diverse lead(ii) coordination compounds was assembled from two isomeric nicotinoylhydrazones as neutral ligands and three Pb(ii) salts with different monoanions (chloride, nitrate and thiocyanate) as starting materials. The products were isolated in good yields and were fully characterized, including by single-crystal X-ray diffraction and theoretical methods. Within the six compounds, three feature 2D metal-organic networks, two are 1D coordination polymers, and another one comprises discrete 0D dimeric units. The structures of the latter low dimensional compounds are extendable into 2D supramolecular networks. The topology of the coordination or supramolecular networks is primarily dictated by the geometry of the nicotinoylhydrazone used as a main building block. In contrast, supramolecular interactions are greatly influenced by the choice of the anion in the starting lead(ii) salt, which is demonstrated by Hirshfeld surface analysis. In fact, the topological analysis and classification of metal-organic or supramolecular underlying networks in the obtained compounds was performed, disclosed the hcb, 2C1, gek1, SP 1-periodic net (4,4)(0,2) and 3,4L83 topological types; the latter topology was documented for three compounds, including both coordination and supramolecular networks. In the two compounds containing thiocyanate moieties, there are supramolecular contacts between the thiocyanate anions and lead centres. These were shown by DFT calculations to be strong tetrel bonds (-15.3 and -16.7 kcal mol-1) between the σ-hole of the lead atom and the π-system of the thiocyanate S-C bond.