Self-assembly of manganese(I) and rhenium(I) based semi-rigid ester functionalized M 2 L 2 -type metallacyclophanes: Synthesis, characterization and cytotoxicity evaluation Chowan Ashok Kumar a , D. Divya a , R. Nagarajaprakash a , V. Veena b , P. Vidhyapriya b , N. Sakthivel b, ** , Bala. Manimaran a, * a Department of Chemistry, Pondicherry University, Puducherry, 605014, India b Department of Biotechnology, Pondicherry University, Puducherry, 605014, India article info Article history: Received 7 March 2017 Received in revised form 3 June 2017 Accepted 5 June 2017 Available online 6 June 2017 Keywords: Self-assembly Semi-rigid pyridyl ligand Ester functional group Metallacyclophane Manganese/rhenium Anticancer activity abstract Synthesis of M 2 L 2 -type dinuclear metallacyclophanes [M(CO) 3 Br(m-L)] 2 (1 and 2,M ¼ Mn; 3 and 4, M ¼ Re) has been accomplished using semi-rigid ester functionalized pyridine ligands with organic spacers and metal precursor containing fac-M(CO) 3 corners. The dinuclear metallacyclophanes were synthesized by the reaction of M(CO) 5 Br (M ¼ Mn, Re) and ditopic pyridine ligands (L) (L ¼ 1,2-phenylene diisonicotinate (pdi) and bis(4-(4-pyridylcarboxyl)phenyl)dimethylmethane (bpcpd)) under facile reac- tion conditions. The self-assembled compounds 1e4 were characterized by elemental analysis, IR, NMR, UVeVis absorption and emission spectroscopic techniques. Compounds 1 and 3 were structurally characterized and the molecular masses of 2 and 4 were evaluated by ESI-MS. The anticancer activities of compounds 1e4 were investigated by in vitro cytotoxicity studies against different cancer cell lines as well as on normal cells and MTT assays. Compounds 2 and 4 showed broad-spectrum inhibitory activities on cancer cells in comparison with a reference compound (cisplatin) upon irradiation at l max 365 nm. The UVeVisible absorption spectroscopy-based myoglobin assay further supported the nature of com- pound 2 as a photolabile CO releasing molecule (PhotoCORM). © 2017 Elsevier B.V. All rights reserved. 1. Introduction Over the past two decades, metallasupramolecular chemistry has been playing a prominent role in fabricating diverse shaped two- and three-dimensional metallapolygons via self-assembly strategies by exploiting predesigned organic tectons and inor- ganic metal precursors [1e8]. Among the various kinds of transition metal based metallasupramolecules, metallacyclic compounds having a fac-M(CO) 3 core (M ¼ Mn, Re) and comprising different cavity dimensions were developed by the judicious choice of diversely shaped organic building blocks [9e15]. For instance, a rhenium(I) based dinuclear metallacyclophane was synthesized by the self-assembly of [Re(CO) 5 Cl] and N-(2-hydroxybenzylidene)- benzimidazole (Hbzp) [16]. Furthermore, synthesis of the Re(I) complexes [Re(CO) 3 (SSCs)] 2 derived from Re(CO) 5 Br and N,N- disubstituted salicylaldehyde semicarbazone (SSCs) and their cytotoxicity studies were recently reported [17]. On the other hand, a rhenium(I)-based helicate was self-assembled using synthesized by treating semi-rigid bis-chelating ligand 1,4-bis(2-(2- hydroxyphenyl)benzimidazol-1-ylmethyl)benzene, flexible bis(- monodentate) nitrogen donor 1,4-bis(benzimidazol-1-ylmethyl) benzene and Re 2 (CO) 10 in a one-step process [18]. For the rational design of dinuclear metallacyclophanes, shape, flexibility, ligand donor sites and coordination sites and angles of metal centers have to be considered [19e21]. In self-assembly process, flexible linkers offer distinct advantages such as adaptive recognition properties and breathing ability to the end molecules in the solid state, whereas semi-rigid linkers offer distinguishable shape to the resulting species like molecular rotors and helicates [18,22e30]. Besides their fascinating structural features, several metal- lacyclophanes have found important applications in sensing, catalysis, luminescence tuning and host-guest chemistry [31e37]. Moreover, these self-assembled facial tricarbonyl core-based * Corresponding author. ** Corresponding author. E-mail addresses: puns2005@gmail.com (N. Sakthivel), manimaran.che@ pondiuni.edu.in (Bala. Manimaran). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2017.06.003 0022-328X/© 2017 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 846 (2017) 152e160