High-pressure single crystal X-ray diffraction study of the linear metal chain compound Co3(dpa)4Br2·CH2Cl2.

S R Madsen,B B Iversen,J Overgaard,D Stalke

doi:10.1039/c5dt00447k

Abstract

The crystal structure of the linear metal chain compound Co3(dpa)4Br2·CH2Cl2 (1) has been investigated up to a pressure of 13.6(2) GPa in a diamond anvil cell (DAC) using single crystal X-ray diffraction. The structure remains orthorhombic as the unit cell volume is reduced by 30% at 12.8 GPa. At 13.6(2) GPa the diffraction pattern is of very poor quality and not even reliable unit cell parameters can be determined. Peak broadening resulting from non-hydrostatic conditions was avoided by annealing the loaded DAC prior to data collection, allowing reliable structural models to be refined up to a pressure of 11.8(2) GPa. On increasing pressure, the disordered CH2Cl2 crystal solvent molecule gradually becomes redistributed from one site to another. Hirshfeld surface analysis suggests that the redistribution is a result of repulsive HH interactions. Pressure also affects the molecular geometry, in particular the Co-Co and Co-Br bond lengths which decrease by 4% and 12%, respectively, at 11.8(2) GPa.

Highlights

The effect of pressure on transition metal coordination complexes is a new and highly active field of research, providing interesting new knowledge about the geometric flexibility, physical properties, and high-pressure chemistry of a diverse range of compounds.[1]
The extended metal atom chain (EMAC) have been intensely studied for their resemblance to electrical wires and their peculiar metal–metal bonding properties.[2]
One of the most intensively studied compounds is Co3(dpa)4Cl2·nCH2Cl2 which is found in a symmetrical form when n = 1, and an unsymmetrical form when n = 2.2a,3 In the symmetrical form of the complex the lengths of the two Co–Co bonds are identical, whereas in the unsymmetrical form there is a difference between the two Co–Co bond lengths of 0.15 Å at ambient conditions.[4]

Summary

Introduction

The effect of pressure on transition metal coordination complexes is a new and highly active field of research, providing interesting new knowledge about the geometric flexibility, physical properties, and high-pressure chemistry of a diverse range of compounds.[1]. Much higher pressures have been applied to 1 (up to 13.6(2) GPa) using a diamond anvil cell (DAC), and the structural changes have been followed using single crystal X-ray diffraction.

Results

Conclusion