In the Laboratory
W
Network Complexes of Copper(I) Halides Robert D. Pike,* Peter M. Graham, Kathryn A. Guy, T. Jason Johnson, Jenine R. Cole, Sarah M. Stamps, and Lauren E. Klemmer Department of Chemistry, College of William and Mary, Williamsburg, VA 23187-8795; *
[email protected] In connection with the “nanotechnology” trend, there is growing interest in metal-organic materials chemistry (1, 2). It is increasingly desirable for college chemistry majors to be exposed to a variety of macromolecular systems. Undergraduate experiments in organic (3) and inorganic (4) polymers and inorganic materials (5) have been reported. However, metal-organic network experiments are lacking. This simple and inexpensive exercise introduces undergraduates to selfassembled metal-organic coordination networks. It also provides applications of many core chemical concepts: coordination chemistry, bridging versus chelating ligand behavior, crystal field theory, equilibrium, kinetic versus thermodynamic products, charge transfer, and spectroscopy. At the College of William & Mary, the experiment is carried out by secondsemester sophomores intending to major in chemistry. These students have taken one semester of general and two of organic chemistry. Nevertheless, the experiment is remarkably flexible and can be incorporated from the freshman through the senior level with slight variations in emphasis. Overview The experiment involves the synthesis, equilibration, and metal analysis of [CuX(Bpy)] and [(CuX)2(Bpy)]; X is Cl, Br, I; Bpy is 4,4′-dipyridyl (6, 7 ). The structures of these compounds are two-dimensional networks, as shown below.1 N
N
Cu X
Cu X
X
N
N
Cu X
X
N
N
N
X
X
N
N
N
Cu X
N
N
The [CuX(Bpy)] complexes (except X = I) show a slightly enhanced stability region.
N
X
X Cu
N
N
Table 1. MeCN Solution Volumes Combined in Part B
A portion of the network structure of [CuX(Bpy)] X
X Cu
N
N
Cu
X
Cu
N
N
X X
Cu
X Cu
N
N
Cu
X
Cu
N
N
X X
Cu
X Cu
N
N
Cu
X
Cu
N
N
X X
Cu
X Cu
X
N
N
Cu
Cu
N
N
X
A portion of the network structure of [(CuX)2(Bpy)]
The exercise has three discrete parts, all of which can be accomplished in a single four-hour laboratory session or which may be divided over two or more sessions. 1522
(3)
Cu X
Cu
Cu
2CuX(soln) + Bpy(soln)
CuX/ Bpy ratio ≥ 2.0. The only solid produced should be yellow [(CuX)2(Bpy)]. Any excess CuX will remain in solution.
X Cu
Cu
N
(2)
CuX/ Bpy ratio >1.0–
