Isolation of a Metastable Intermediate in a Heterometallic Cu II -Hg II 1D Polymeric Chain: Synthesis, Crystal Structure, and Photophysical Properties Shaikh M. Mobin,* Veenu Mishra, and Archana Chaudhary Discipline of Chemistry, School of Basic Sciences, Indian Institute of Technology Indore, Khandwa Road, Indore 452017, India * S Supporting Information ABSTRACT: A metastable heterometallic intermediate, [Cu 2 (bpy) 2 (DIPSA) 2 Hg 2 (OAc) 4 (DIPSA) 2 ] n (1, where OAc = CH 3 COO - , bpy = bipyridine, and DIPSA = diisopropylsalicylic acid), has been isolated and characterized during the synthesis of 1D polymer [Cu 2 (bpy) 2 (DIPSA) 2 (CH 3 CN) 2 Hg 2 (OAc) 2 (DIPSA) 4 ] n (2) at ambient temperature in acetonitrile. Moreover, recrystallization of 2 in methanol results in monomeric [Cu(DIPSA)(bpy)(CH 3 OH)]·CH 3 OH (3). Complexes 1-3 have been characterized by elemental analysis, Fourier transform infrared, and UV-vis spectroscopy as well as by their single-crystal X-ray structures. The photophysical study suggests the quenching of fluorescence of DIPSA upon complexation. ■ INTRODUCTION Heterometallic transition-metal coordination polymers repre- sent an actively pursued topic in modern coordination chemistry, 1 reflecting the fact that heterometallic complexes have significant applications in catalysis, 2 electrical conductiv- ity, 3 sensing, 4 and magnetism. 5 Heterometallic catalysts, where multiple metal centers are present in close proximity to each other, exhibit better reactivity than equivalent mixtures of monometallic complexes. 2c,6 Moreover, heterometallic coordi- nation polymers are also appealing from the crystallographic point of view owing to their diverse geometrical arrangements. 7 Out of several approaches for the construction of heterometallic complexes, one is based on the idea that different metals show different affinities for a particular donor atom and, thus, the addition of a ligand possessing different donor atoms with a mixture of metals leads to self-assembled or well-ordered heterometallic systems. 8 In the 5d transition metals, Hg is known to be a good candidate for generating heterometallic complexes with various other metal ions. 9 It forms dinuclear, trinuclear, tetranuclear, and polynuclear complexes with different metals; however, it exhibits a better compatibility with Cu II metal. 10 These aspects extend the impetus to introduce newer routes for the construction of heterometallic complexes. Moreover, the isolation and structural characterization of a metastable intermediate is a formidable challenge. In the literature, there are only a few reports dealing with structurally characterized discrete meta- stable intermediates. 11 Herein, we report the isolation as well as structural characterization of a kinetically controlled metastable hetero- metallic 1D polymeric intermediate, [Cu 2 (bpy) 2 (DIPSA) 2 Hg 2 - (OAc) 4 (DIPSA) 2 ] n (1, where OAc = CH 3 COO - , bpy = bipyridine, and DIPSA = diisopropylsalicylic acid), along with the thermodynamically driven Cu II -Hg II 1D polymeric chain [Cu 2 (bpy) 2 (DIPSA) 2 (CH 3 CN) 2 Hg 2 (OAc) 2 (DIPSA) 4 ] n (2) and a monomeric Cu II complex, [Cu(DIPSA)(bpy)- (CH 3 OH)]·CH 3 OH (3), obtained during recrystallization of 2 in methanol (MeOH). To the best of our knowledge, this is the first report dealing with the structural characterization of a heterometallic 1D polymer chain intermediate. ■ RESULTS AND DISCUSSION Coordination polymer 2 was synthesized via the reaction of Hg(OAc) 2 , Cu(OAc) 2 ·H 2 O, bpy, and DIPSA in acetonitrile (ACN) at 298 K. The initial reaction mixture was dark green after 3 h and turned to light green within 12 h. A fraction of the dark-green reaction mixture was therefore extracted after 3 h, and a single spot on the thin-layer chromatography (TLC) plate ensured the presence of only one component. Its subsequent crystallization established the isolation of the kinetically driven intermediate 1. The further extension of the same reaction up to 12 h led to the isolation of the thermodynamically stable form 2 (Scheme 1). Moreover, Received: August 16, 2014 Published: January 23, 2015 Article pubs.acs.org/IC © 2015 American Chemical Society 1293 DOI: 10.1021/ic502514e Inorg. Chem. 2015, 54, 1293-1299