Impact of ligand substituents on the crystal structures, optical and conducting properties of phenylmercury(II) β-oxodithioester complexes

Highlights

• Five new Phenylmercury(II) β-oxodithioester complexes have been synthesized and characterized.

• Linear two-coordinate geometry about the Hg atom is revealed in all the complexes.

• Complex 1 show interesting intermolecular Hg···N and Hg···S interactions generating a 2-D net-like polymeric structure.

• Solution and solid phase photoluminescent properties have been investigated.

Abstract

New phenylmercury(II) complexes 1–5 with functionalized β-oxodithioester ligands, [PhHg(II) (β-oxodithioester)], β-oxodithioester = methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate L1 1, methyl-3-hydroxy-3-(p-chlorophenyl)-2-propenedithioate L2 2, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate L3 3, methyl-3-hydroxy-3-(9-anthracenyl)-2-propenedithioate L4 4 and methyl-3-hydroxy-3-(p-fluorophenyl)-2-propenedithioate L5 5, were synthesized and characterized by elemental (C, H, N) analysis, IR, UV-Vis., ¹H and ¹³C{¹H} NMR spectroscopy. Their structures have been investigated by single crystal X-ray diffraction. Linear two-coordinate geometry about the Hg atom, via ipso-C of the phenyl group and by S15 atom of the β-oxodithioester ligands is revealed in all complexes. Intramolecular Hg···O bonding at 2.622(10)–2.813(6) Å is present in all the complexes. In 1–3, the asymmetric unit contains a single discrete molecule whereas complexes 4 and 5 contain two. Except for 4 having bulky anthracene substituent, intriguing supramolecular networks are sustained through intermolecular metal assisted Hg···S and Hg···N and Cl···Cl, Cl···π, S···S, C–H···S, C–H···F, C–H···π interactions in these complexes. In 1 the pyridyl N on 4-position on the substituent is involved in Hg···N bonding interactions on the neighboring molecule at 2.938(7) Å generating a 2-D net-like polymeric structure. All the complexes showed bright green luminescent emissions both in solution and solid phase. The complexes (σ_rt values = 10⁻³–10⁻⁶ S cm⁻¹) show semiconducting characteristics with Ea values = 0.14–0.64 eV. The electronic and steric properties of the substituents on the dithioester unit significantly influence their structures and properties.

Introduction

There has been significant growth of interest in the coordination chemistry of organomercury(II) and mercury(II) compounds not only to gain understanding concerning mercury-cysteine interactions in biological processes which can lead to severe health hazards causing damage to brain and endocrine system, environmental pollution and possible chemical antidotes, but also because of their intriguing structural chemistry and material properties [1], [2], [3], [4], [5], [6], [7]. The chemistry of metal complexes including mercury with 1,1-dithiolato ligands, such as dithiocarbamate, xanthate and dithiophosphate containing identical S,S-donor atoms have been widely explored because of their multifaceted chemistry and applications in diverse areas [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Metal complexes of related dithioester ligands have been reported [18,19] but their structural investigations, study of properties and applications have gained little attention [20], [21], [22] although in recent years some main group and transition metal have been studied [20,21].

The developing interest in dithioester ligand chemistry is due to the functionalization of substituents that may substantially give rise to intriguing structures and modified physical properties. It is therefore crucial to make changes to ligand substituents with varied electronic and steric characteristics to map out the structures and properties of their complexes. With this in mind, in this contribution we report on the syntheses, crystal structures, luminescent and conducting properties of five new phenylmercury(II) complexes with pyridyl 4(N), p-chlorophenyl, 2-naphthyl, 9-anthracenyl and p-fluorophenyl functionalized β-oxodithioester ligands (Scheme 1). The important perspectives of pursuing this work are: (i) unlike 1,1-dithio ligands with soft bidentate S,S- donors, the β-oxodithioesters having both soft S and hard O donor atoms may expand their bonding ability with a variety of hard and soft metal ions. Usually the O,S-coordination mode of the β-oxodithioester ligands stabilize six-membered chelate ring in comparison to strained four-membered chelate rings formed by 1,1-dithio ligands about the metal centre; (ii) the compounds of mercury(II), with d¹⁰ electronic configuration do not feature ligand field bands and as a result their coordination numbers as well as structures are not imposed by ligand field stabilization requirements. The usual coordination numbers exhibited are 2 and 4 with linear/tetrahedral arrangements, however higher coordination numbers 3, 5 and 6 are also stabilized with weaker metal assisted bonding interactions. In-spite of the strength of Hg−S bond, the Hg···S and Hg···O interactions play crucial roles in the organization of supramolecular motifs. The incorporation of substituents on the dithioester backbone with varied steric bulk and different donor atoms N, Cl or F may induce secondary bonding interactions and increase the dimensionality of the complexes; (iii) the luminescent properties of divalent group 12 metal complexes particularly with Zn and Cd [5b,5d,[23], [24], [25], [26]] are well documented, however studies on mercury complexes are rather scant. The more electronegative oxygen with small p-orbitals and less electronegative sulfur with more diffused d-orbitals within the molecules may modify the HOMO-LUMO gap and hence vary luminescent characteristics; and (iv) the sulfur rich planar metal complexes exhibited interesting conducting properties in solid state because of effective S···S intermolecular contacts [14], [15], [16]. The non planar complexes of chalcogenocyanates though limited in number, have also displayed interesting conducting characteristics [27,28].