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Ionic liquids comprising cationic Pd II complexes with SNS-pincer ligands ([Pd(L SNS )Me] + ([ 1 ] + ) and [Pd(L SNS )Cl] + ([ 2 ] + ); L SNS = 2,6-bis( n -butylthiomethyl)pyridine) and bis(trifluoromethanesulfonyl)amide (Tf 2 N) or tetrafluoroborate (BF 4 ) anions were prepared, and the effect of ancillary ligands on their thermal properties and solvent polarities were investigated. [ 1 ]Tf 2 N and [ 2 ]Tf 2 N were liquids and exhibited glass transitions at −47 °C and −23 °C, and their solvent polarity parameters ( E N T ) were 0.51 and 0.46, respectively. [ 1 ]BF 4 and [ 2 ]BF 4 were solids with melting points of 73.2 °C and 141.5 °C, respectively. X-ray structure determination of [ 2 ]BF 4 revealed a structure with alternating ionic and non-polar alkyl chain layers.

The structural change associated with the first-order phase transition ( T C = 155.1 K) in a mixed-stack charge-transfer complex (octamethylferrocene)(2,3-dichloro-1,4-naphthoquinone) 2 was investigated crystallographically. X-ray structure determination at 90 K revealed that the transition is associated with the order-disorder of the C 5 Me 4 H ring in octamethylferrocene. In the low temperature phase, tripling of the unit cell occurred, accompanied by a change in spacegroup from P 2 1 /c to P −1, and every third octamethylferrocene molecule twists out of the plane to minimize steric interactions.

Organometallic charge-transfer salts composed of decamethyl-, octamethyl-, and dimethylferrocene with N,N′-dicyano-1,4-benzoquinonediimine (DCNQI) derivatives were prepared. [Fe(C5Me5)2][(MeO)2DCNQI] (1) and [Fe(C5Me4H)2][Me2DCNQI] (2) were 1:1 DA salts with mixed-stack structures, whereas [Fe(C5Me4H)2][(MeO)2DCNQI]2 (3) and [Fe(C5MeH4)2][DCNQI]2 (4) were 1:2 DA salts. 3 exhibited a segregated-stack structure, in which charge separation was observed in the acceptor column. 1 became a metamagnet below TN = 5.0 K, whereas the other salts were paramagnets. Valence states and charge-transfer (CT) transitions in these complexes are discussed based on the neutral–ionic (NI) phase diagram.

Decamethylferrocenium salts with perfluoroalkylsulfonate anions ( C n F 2 n + 1 SO 3 − ; n = 1, 4, and 8) and perfluoroalkylcarboxylate anions ( C n F 2 n + 1 CO 2 − ; n = 1–4) were prepared to investigate the effects of the anion on the thermal behaviors of the salts. Differential scanning calorimetry (DSC) measurements revealed that all the salts exhibited phase transitions in the solid state. Salts with an octamethylferrocenium cation or decamethylcobaltocenium cation exhibited different phase sequences from those of the corresponding decamethylferrocenium salts. Structural changes associated with the phase transitions were investigated crystallographically for two salts. The phase transition in [Fe(C 5 Me 5 ) 2 ](CF 3 SO 3 ) at −121.6 °C was accompanied by ordering of the cation conformations into eclipsed and staggered conformations in different ratios. The unit cell volume became six times larger and the space group changed from P mn2 1 to P 1 in the low-temperature phase. The phase transition in [Fe(C 5 Me 5 ) 2 ](C 3 F 7 CO 2 ) at −115 °C was not accompanied by any change in the unit cell or the space group ( P 2 1 / c ). The libration or displacements of the anions that existed in the high-temperature phase was suppressed in the low-temperature phase, associated with a slight rotational displacement of the molecules. Anions with longer perfluoroalkyl chains exhibited disorder in the solid state even at low temperatures.