Three-coordinate [Cu(II)X(3)](-) (X=Cl, Br), trapped in a molecular crystal

Area of Science:

• Inorganic Chemistry
• Crystallography
• Computational Chemistry

Background:

• Three-coordinate copper(II) complexes with monatomic halide ligands are uncommon.
• The coordination chemistry of copper(II) is typically four-coordinate or higher.

Purpose of the Study:

• To synthesize and characterize novel three-coordinate copper(II) complexes with mixed chloride and bromide ligands.
• To investigate the structural and electronic properties of these complexes using experimental and computational methods.

Main Methods:

• Crystallization of copper(II) halide mixtures with [Ph(3)PNPPh(3)](+)Cl(-).
• Single-crystal X-ray diffraction analysis.
• Density Functional Theory (DFT) calculations.

Main Results:

• Isolation of three-coordinate copper(II) complexes with mixed chloride and bromide ligands: [Ph(3)PNPPh(3)](+)[CuCl(0.9)Br(2.1)](-) and [Ph(3)PNPPh(3)](+)[CuCl(2.4)Br(0.6)](-).
• Observation of angularly distorted trigonal-planar copper(II) coordination.
• DFT calculations reveal a soft energy surface for angle bending and a flat potential energy surface for secondary coordination by acetonitrile.

Conclusions:

• Three-coordinate copper(II) with monatomic halide ligands is considered normal.
• Steric control is not essential for enforcing three-coordination.
• Hydrophobic aryl environments stabilize these three-coordinate complexes.
• The energy difference between three- and four-coordinate copper(II) is minimal (approx. 5 kcal mol(-1)).