Electronic and Structural Variation among Copper(II) Complexes with Substituted Phenanthrolines

A series of copper(II) complexes with substituted phenanthroline ligands has been synthesized and characterized electronically and structurally. The compounds that have been prepared include the monosubstituted ligand complexes of the general formula [Cu(5-R-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub>, where R = NO<sub>2</sub>, Cl, H, or Me, and the disubstituted ligand complex [Cu(5,6-Me<sub>2</sub>-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub>. The complexes [Cu(5-NO<sub>2</sub>-phen)<sub>2</sub>(CH<sub>3</sub>CN](BF<sub>4</sub>)<sub>2</sub> (<b>1</b>), [Cu(5-Cl-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> (<b>2</b>), [Cu(o-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> (<b>3</b>), and [Cu(5-Me-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> (<b>4</b>) each crystallize in the space group <i>C</i>2/<i>c</i> with compounds <b>1</b>, <b>2</b>, and <b>4</b> comprising an isomorphous set. The disubstituted complex [Cu(5,6-Me<sub>2</sub>-phen)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> (<b>5</b>) crystallizes in the space group <i>P</i>2<sub>1</sub>/<i>c</i>. Each structure is characterized by a distorted trigonal bipyramidal arrangement of ligands around the central copper atom with approximate or exact <i>C</i><sub>2</sub> symmetry. The progression from electron-withdrawing to electron-donating substituents on the phenanthroline ligands correlates with less accessible reduction potentials for the bis-chelate complexes.