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,
N-methylnicotinamide and
N,
N-diethylnicotinamide.
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.