Crystal structures and spectroscopic behavior of monomeric, dimeric and polymeric copper(II) chloroacetate adducts with isonicotinamide, N-methylnicotinamide and N, N-diethylnicotinamide

Abstract

Substituted pyridines provide structural rigidity and thus permit the metal coordination geometry to guide the direction of propagation of the hydrogen-bonded links between building blocks. In this paper we present the crystal structures and spectroscopic properties of monomeric, dimeric and polymeric copper(II) chloroacetates with isonicotinamide (INA), N-methylnicotinamide (MNA) and N, N-diethylnicotinamide (DENA). The molecular structure of [Cu(ClCH 2CO 2) 2(INA) 2] 2 ( 1) consists of a rather interesting dinuclear molecule with copper atoms bridged by anti, anti- O, O′ bridging oxygens of two chloroacetate anions. Each copper atom is octahedrally coordinated thus forming a CuN 2O 4 core with two nitrogens, originating from two different isonicotinamide molecules, in trans positions. This complex is one of a very few examples of this rare type of structure in which both carboxylate oxygen anions are coordinated to two copper metal ions. The crystal structure of 1 revealed an infinite 1-D linear hydrogen-bonded chain formed by discrete molecules [Cu(ClCH 2CO 2) 2(INA) 2] 2 connected by strong hydrogen bonds between two amide groups. This structure is the first example, where two pairs of amide groups are involved in hydrogen bonding connecting two molecules. The X-ray structure of the complex [Cu(CCl 3CO 2) 2(INA) 2] n ( 3) revealed a tetragonal bipyramidal environment about the copper(II) atom. This structure represents the first example of copper(II) complex, where isonicotinamide acts as a bridging ligand. Strong intramolecular hydrogen bonds, N–H⋯O, create two eight-membered metallocycle rings which stabilizes the molecular structure. The crystal structure of 3 consists of 2-D sheets of a metal–organic framework. The coordination environment of the copper(II) atom in [Cu(CCl 3CO 2) 2(MNA) 2(H 2O) 2] · 2H 2O ( 6 · 2H 2O) is an elongated tetragonal bipyramid. Strong intramolecular hydrogen bond interactions involving an axial coordinated water molecule and a carboxylic oxygen atom stabilize the molecular structure. The crystal structure of [Cu 2(ClCH 2CO 2) 4(DENA)] n ( 7) shows that the complex is an extended zigzag coordination chain of alternating binuclear paddle-wheel units of the bridging tetracarboxylate type Cu 2(ClCH 2CO 2) 4 and N, N-diethylnicotinamide molecules. This complex represents the first example of copper(II) carboxylates where N, N-diethylnicotinamide molecule acts as a bidentate bridging ligand connecting binuclear paddle-wheel units. The variation in DENA coordination in the polymeric chain can be described by the following formula: –[Cu 2(ClCH 2CO 2) 4]–(DENA- N, O)– [Cu 2(ClCH 2CO 2) 4]–(DENA- O, N)–. All complexes were characterized by electron paramagnetic resonance (EPR) spectroscopy and IR spectroscopy. The present study shows that the pyridine-carboxyamides are very suitable molecules that can be employed as ligands in the construction of extended arrays of transition metal-containing molecules linked via hydrogen bonds.