A series of new heteroleptic Hg(II) complexes: Synthesis, crystal structures and photophysical properties Shaikh M. Mobin a,b,c,⇑ , Anoop Kumar Saini a , Veenu Mishra a , Archana Chaudhary a,⇑ a Discipline of Chemistry, Indian Institute of Technology Indore, Simrol, Khandwa Road, Indore 452020, India b Discipline of Bioscience and Biomedical Engineering, Indian Institute of Technology Indore, Simrol, Khandwa Road, Indore 452020, India c Discipline of Material Science and Engineering, Indian Institute of Technology Indore, Simrol, Khandwa Road, Indore 452020, India article info Article history: Received 18 December 2015 Accepted 24 February 2016 Available online 4 March 2016 Keywords: Heteroleptic Bipyridine Mercury Polymer Benzoic acid abstract We report the synthesis of six new heteroleptic Hg(II) complexes (1–6) with general composition [Hg(II) (bpy)L 2 ] where bpy = 2,2 0 -bipyridine, L = benzoic acid (1), 2-amino benzoic acid (2), 3-amino benzoic acid (3), 4-amino benzoic acid (4), 2-hydroxy benzoic acid (5), 4-hydroxy benzoic acid (6). 1, 2, 4–6 are mono- mer with hexa coordinated Hg(II) center whereas 3 is a zig–zag 1D-polymer with hepta-coordinated Hg (II) ion. Unlike other substituted benzoic acids, the 3-amino benzoic acid shows both –NH 2 and –COOH groups having affinity towards Hg(II) centers. Therefore, on reaction of HgCl 2 /HgBr 2 with 3-amino ben- zoic acid it was observed that only –NH 2 group coordinates to Hg(II) center and –COOH group remains uncoordinated yielding 7 and 8. 1–6 have been characterized by elemental analysis, FT-IR, thermo gravi- metric analysis as well as single crystal X-ray studies. Their photo-physical properties were also investi- gated and maximum quantum yield was observed for 3. Polymer 3 exhibited different fluorescence spectra in different solvents with maximum emission in chloroform. The electronic communication and geometry optimization have been performed by Density Functional Theory. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Mercury is a poisonous metal and its traces may be harmful to the human body so in the recent past there is rapid development in the research of mercury sensor and detection [1–3]. Mercury has the ability of forming amalgam with almost all the metals and its copper/silver/tin amalgam is used for dental filling [4]. Generally, Hg(II) compounds find potential applications in paper industry, cosmetics, preservatives, paints, thermometers, energy efficient fluorescent light bulbs and mercury batteries [5]. Recently applica- tions such as the antimicrobial, antibacterial, and antineoplastic of some Hg(II) complexes have been found of interest for biologist and chemist [6]. DNA–Hg complex is also useful in the probing defects in DNA [7]. The d 10 configuration of Hg(II) is accompanied by a flexible coor- dination environment in such a way that the geometries of its coor- dination complexes may vary from distorted T-shape to octahedral to regular polyhedron. The d 10 metal ion complexes are generally labile and formation of coordination bonds between metal ion and donor atoms of the ligand is reversible, due to this, the ligand and metal centers may rearrange during polymerization process generating highly ordered networks [8]. Consequently, Hg(II) exhi- bits the ability of forming all kinds of architectures viz. 1D, 2D and 3D polymers [5,9–12]. Carboxylic acids are versatile ligands, show- ing different coordination modes, monodentate, chelate, and differ- ent types of bridges [13]. Complexes of Hg(II) with various aliphatic and aromatic carboxylic acids are well documented. For instance- mercury compounds containing acetic acid [14] trifluroacetic acid [15] aminomethylphosphonic acid [16] 3-hydroxypiconic acid [17] 4-pyridylthioacetic acid [18] pyridine-3-carboxylic acid [19] 2,6-pyridynedicarboxylic acid [20–21] 2-pyridinephosphonic acid [22] have been thoroughly characterized. This literature survey prompted us to carry out a systematic study on the Hg(II) com- plexes containing mixed ligands. The aromatic carboxylic acid bear- ing another acidic or basic substituents have been used to observe the role of substituent in architect formation. Herein, we report the synthesis and characterization of eight new Hg(II) complexes, with 2,2 0 -bipyridine and amino/hydroxy-benzoic acids, their photophys- ical properties and theoretical calculations. 2. Result and discussion Heteroleptic complexes 1–6 are obtained by reaction of Hg (OAc) 2 , bpy [OAc = CH 3 COO, and bpy = 2, 2 0 -bipyridine] and varying http://dx.doi.org/10.1016/j.poly.2016.02.037 0277-5387/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors at: Discipline of Chemistry, Indian Institute of Technol- ogy Indore, Simrol, Khandwa Road, Indore 452020, India (S.M. Mobin, A. Chaudhary). E-mail addresses: xray@iiti.ac.in (S.M. Mobin), archana19jpr@gmail.com (A. Chaudhary). Polyhedron 110 (2016) 131–141 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly