The pressure tunning Raman and IR spectral studies on the multinuclear metal carbyne complexes

The Raman and infrared (IR) spectra of four tungsten metal carbyne complexes I, II, IV and V [Cl(CO)₂(L)WCC₆H ₄(CCC₆H₄)_nNC]₂M (L = TMEDA, n = 0, M = PdI₂ or ReCl(CO)₃; L = DPPE, n = 1, M = PdI₂ or ReCl(CO)₃) were studied at high external pressure. Their pressure-induced phase transitions were observed near 20 kbar (complexes I), 15 kbar (complexes II), 25 kbar (complex IV) and 30 kbar (complex V). The pressure-induced phase transition likely is first order in complex I and the pressure-induced phase transitions of complexes II, IV and V are mostly second order. The pressure sensitivities dν/dp of ν(WC) are high in the low-pressure phase area and very low in the high-pressure phase area due to the pressure strengthening π back-bonding from metal W to π^* orbital of CO in fragment Cl(CO)₂(L)WC. The pressure strengthening metal π back-bonding from metal Re or Pd to π^* orbital of CO or CN also happened to both of central metal centers of NCPd(I ₂)CN in complex I and NCReCl(CO)₃CN in complex II.