PHYSICAL-PROPERTIES OF QUASI-ONE-DIMENSIONAL CHARGE-TRANSFER METAL-COMPLEXES - [M(HBQD)(2)]TCNQ (M=NI, PD - H(2)BQD=1,2-BENZOQUINONEDIOXIME)

We have investigated the physical properties of [M(HBQD)(2)]TCNQ (M=Ni , Pd; H(2)BQD=1,2-benzoquinonedioxime) which consist of alternating -D -A-D-A- type stackings of transition-metal-complex donors and organic TCNQ accepters. The degree of charge-transfer for each sample was esti mated to be -0.1 from the results of IR, Raman spectra, and bond lengt h of TCNQ. From XPS measurements, the valence state of Ni or Pd was fo und to be transformed at low temperature from +II to the mixed valency of +II,+III or +II,+IV, respectively. This behavior can be considered to be due to the charge-transfer from d-orbital of the transition met al to pi-antibonding orbital of the HBQD ligands, which was confirmed by the lower-energy shift of IR stretching modes of C=N in HBQD. This temperature-induced charge-transfer between transition metal and ligan d is the first observation in the transition-metal-complex assemblies.