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Hexaazamacrocyclic Nickel and Copper Complexes and their Reactivity with Tetracyanoquinodimethane

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posted on 14.05.2007 by Loreto Ballester, Angel Gutiérrez, M. Felisa Perpiñán, Ana E. Sánchez, Marina Fonari, Maria Gdaniec
The hexaazamacrocycle 1,4,7,10,13,16-hexaazacyclooctadecane, [18]ane-N6, forms mono- and dinuclear derivatives with copper chloride depending on the reaction stoichiometries and times. The mononuclear derivative, [Cu([18]ane-N6)]Cl2·H2O, presents the macrocycle wrapped around the metal atom in a distorted octahedral coordinative environment, while the dinuclear derivative, [Cu2([18]ane-N6)Cl2]Cl2·4H2O, is formed by a central Cu2Cl2 core surrounded by an almost planar macrocycle. The crystal structure of both derivatives is stabilized by a network of hydrogen bonds involving the amine macrocyclic groups, the chloride anions, and the crystallization water molecules. The copper atoms in the dinuclear derivative show a strong antiferromagnetic coupling, as expected for the crystal structure parameters. A mononuclear nickel derivative has also been obtained from nickel nitrate by following the same synthetic procedure. These compounds react with TCNQ salts with formation of two types of derivatives, [M([18]ane-N6)](TCNQ)2 and [M([18]ane-N6)](TCNQ)4, depending on the use of radical-anionic or mixed-valence TCNQ salts in the reaction. The crystal structures of the nickel derivatives show that the former derivatives are built up by macrocyclic metal cations surrounded by dimeric dianions (TCNQ)22-, either isolated or stacked along the crystal. The derivative with four TCNQ units/formula consists of alternated chains of metallomacrocyclic cations and stacked TCNQ anions. The crystal parameters suggest that every TCNQ holds approximately 0.5 electrons and overlaps with a neighboring unit to form dimeric monoanions, (TCNQ)2-.