X-ray and optical studies of one-dimensional bis(dimethylglyoximato)Pd(II), Pd(dmg)2 at high pressures

By use of synchrotron radiation, powder x-ray diffraction of one-dimensional bis(dimethylglyoximato)Pd(II), Pd(dmg)2 has been studied at high pressures. The lattice constants with an orthorhombic structure for Pd(dmg)2 decreased with increasing pressure up to 10 GPa. The rate of the decrease of the b-axis was lower than that of the a-axis above 3 GPa. The c-axis is very compressible. A Pd-Pd distance along the c-axis abruptly decreased from 3.255 °A at ambient pressure to 2.82 °A at 7.4 GPa. A bulk modulus was estimated from the volume vs. pressure curve fitted by a Birch equation of state. The bulk modulus and its derivative of Pd(dmg)2 were 9.9(7) GPa and 9.2(8). This complex is a very compressible compound. The electronic absorption spectra of a thin film of Pd(dmg)2 have been investigated at high pressures. The 4d–5p transition bands rapidly shifted to lower energy region with increasing pressure. This optical transition energy decreased linearly with decreasing Pd-Pd distance. The optical property of Pd(dmg)2 shows the one-dimensional character in the 0–6 GPa region.