Cu<sup>II</sup>-Azide Polynuclear Complexes of Three
Different Building Clusters with the Same Schiff-Base Ligand: Synthesis,
Structures, Magnetic Behavior, and Density Functional Theory Studies
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Abstract
Three
copper-azido complexes [Cu<sub>4</sub>(N<sub>3</sub>)<sub>8</sub>(L<sup>1</sup>)<sub>2</sub>(MeOH)<sub>2</sub>]<sub><i>n</i></sub> (<b>1</b>), [Cu<sub>4</sub>(N<sub>3</sub>)<sub>8</sub>(L<sup>1</sup>)<sub>2</sub>] (<b>2</b>), and [Cu<sub>5</sub>(N<sub>3</sub>)<sub>10</sub>(L<sup>1</sup>)<sub>2</sub>]<sub><i>n</i></sub> (<b>3</b>) [L<sup>1</sup> is the imine resulting
from the condensation of pyridine-2-carboxaldehyde with 2-(2-pyridyl)ethylamine]
have been synthesized using lower molar equivalents of the Schiff
base ligand with Cu(NO<sub>3</sub>)<sub>2</sub>·3H<sub>2</sub>O and an excess of NaN<sub>3</sub>. Single crystal X-ray structures
show that the basic unit of the complexes <b>1</b> and <b>2</b> contains Cu<sup>II</sup><sub>4</sub> building blocks; however,
they have distinct basic and overall structures due to a small change
in the bridging mode of the peripheral pair of copper atoms in the
linear tetranuclear structures. Interestingly, these changes are the
result of changing the solvent system (MeOH/H<sub>2</sub>O to EtOH/H<sub>2</sub>O) used for the synthesis, without changing the proportions
of the components (metal to ligand ratio 2:1). Using even lower proportions
of the ligand, another unique complex was isolated with Cu<sup>II</sup><sub>5</sub> building units, forming a two-dimensional complex (<b>3</b>). Magnetic susceptibility measurements over a wide range
of temperature exhibit the presence of both antiferromagnetic (very
weak) and ferromagnetic exchanges within the tetranuclear unit structures.
Density functional theory calculations (using B3LYP functional, and
two different basis sets) have been performed on the complexes <b>1</b> and <b>2</b> to provide a qualitative theoretical
interpretation of their overall magnetic behavior
