Polyhedron 20 (2001) 899 – 904
Coordination polymers of copper(II) based on mixed N- and
O-donor ligands: the crystal structures of [CuL
2
(4,4-bipy)]
n
(L = lactate or 2-methyllactate)
Rosa Carballo
a,
*, Alfonso Castin ˜ eiras
b
, Berta Covelo
a
, Ezequiel M. Va ´zquez-Lo ´ pez
a
a
Departamento de Quı ´mica Inorga ´nica, Facultade de Ciencias -Quı ´mica, Uniersidade de Vigo, E-36200 Vigo, Galicia, Spain
b
Departamento de Quı ´mica Inorga ´nica, Facultade de Farmacia, Uniersidade de Santiago de Compostela,
E-15706 Santiago de Compostela, Galicia, Spain
Received 3 November 2000; accepted 18 December 2000
Abstract
The neutral polymeric complexes of copper(II) [CuL
2
(4,4-bipy)]
n
, where L is an -hydroxycarboxylato ligand, lactate in 1,
2-methyllactate in 2, were prepared and characterised structurally. The copper atom is in an elongated tetragonally distorted
octahedral environment in both compounds. Both -hydroxycarboxylato ligands are O,O-bidentate chelating monoanions and
4,4-bipyridine acts as an N,N-bis(monodentate) bridging ligand creating a linear polymeric arrangement. The polymeric chains
are interconnected by O
hydroxyl
H···O
carboxy
hydrogen bonds in a way that creates cavities that differ in size between 1 and 2.
Spectroscopic data are presented and discussed. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Mixed-ligand coordination polymers; -Hydroxycarboxylato ligands; 4,4-Bipyridine ligand; Copper(II) complexes; Crystal structures;
Supramolecular arrays
www.elsevier.nl/locate/poly
1. Introduction
In recent years, considerable research effort has been
focused on the crystal engineering of supramolecular
structures, which have a wide variety of network to-
pologies and potential applications in the fields of
catalysis, electrical conductivity, molecular magnetic
materials and host – guest chemistry [1 – 3]. Although
purely organic systems have been widely studied, their
inorganic counterparts based on coordination com-
plexes have only recently received significant attention
[4]. Strategies for the construction of coordination poly-
mers with two-dimensional (2D) or three-dimensional
(3D) frameworks have focused on the use of directional
interactions such as hydrogen bonding and dative coor-
dinate bonding to control the aggregation of molecular
species. So far a number of 1D, 2D and 3D infinite
frameworks have been generated using linear bidentate
N,N-donor compounds. For example, the linear chain
structures that are formed by coordination of 4,4-
bipyridine (4,4-bipy) to metal centres can be worked up
into polymers of higher dimensionality through other
connections. Generally, such polymers are formed by
just one type of organic ligand (a ‘spacer’ such as
4,4-bipy, pyrazine, 1,2-bis(4-pyridyl)ethene, etc.) to-
gether with a variety of inorganic anions [1,5 – 19].
Much less is known of systems containing two different
organic ligands, although there have been reports of
several interesting examples with the ligand combina-
tions oxalate +4,4-bipy [20], hexafluoroacetylaceto-
nate +4,4-bipy or 4,4-bipyridyl-N,N -dioxide [21],
phthalate +4,4-bipy [22], malonate +4,4-bipy [22,23],
chloranilate +pyrazine [24], pyridine-4-carboxylate +
4,4-bipy [25] and acetate +4,4-bipy [13,26].
We report here the synthesis and structures of two
mixed-ligand systems in which one component is the
spacer 4,4-bipy and the other an -hydroxycarboxylato
ligand [lactate or -hydroxyisobutyrate(2-methyllac-
tate)]. The -hydroxy acid derivatives act as bidentate
ligands and at the same time serve to construct super-
* Corresponding author. Tel.: +34-986-812273; fax: +34-986-
812382.
E-mail address: rcrial@uvigo.es (R. Carballo).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII:S0277-5387(01)00749-5