PRESSURE-INDUCED ISOMERIZATIONS IN 5-COORDINATE SOLID-STATE COPPER(II) COMPLEXES

The effects of high pressure on [Cu(phen)2(OH2)](BF4)2 (1) (phen = 1,10-phenanthroline), [Cu(bipy)2(OH2)](S2O6) (2) (bipy = 2,2'-bipyridyl), and [Cu(bipy)2Cl]X (X = ClO4 (3), NO3.3H2O (4), PF6.H2O (5), and Cl.6H2O (6) are described. The complexes contain CuN4X (X = O or Cl) chromophores and represent a series of structures along a structural pathway between trigonal bipyramidal and square pyramidal geometries. Two square pyramidal structures are possible depending on whether X occupies an apical or basal position. Elongated apical Cu-O bonds are present in distorted square pyramidal 1 and 2 at ambient pressure. Pressure tuning spectroscopy indicates apical compression and isomerization to distorted basal square pyramidal geometry in 1 and 2 at high pressure. Pressure-induced isomerizations toward regular basal square pyramidal geometries are observed in distorted basal square pyramidal 3 and regular trigonal bipyramidal 5. No significant changes were observed in 4 (distorted basal square pyramidal) and 6 (regular trigonal bipyramidal), possibly because of the extended hydrogen-bonding network present in these two complexes. As has previously been observed for other sets of complexes, the spread of chromophore configuration for various counterions is considerably less at high pressure than at ambient pressure.