The complexes [Fe(CCR)(L–L)(η-C₅R′₅)][R = Bu^t, CO₂Me, CO₂Et, SiMe₃, Ph or CH₂OMe, L–L = Ph₂PCH₂PPh₂(dppm), R′= H; R = Bu^t or Ph, L–L = Ph₂PCH₂CH₂PPh₂(dppe), R′= Me] undergo reversible one-electron oxidation at a platinum electrode in CH₂Cl₂. Chemical oxidation with [Fe(η-C₅H₅)₂][PF₆] gave the isolable salts [Fe(CCR)(dppe)(η-C₅Me₅)][PF₆](R = Bu^t or Ph) which Mössbauer spectroscopy suggests to be complexes of Fe^III. The ESR spectra of these salts, and of the cations [Fe(CCR)(dppm)(η-C₅H₅)]⁺(R = Bu^t, CO₂Me, CO₂Et or Ph), generated by in situ oxidation with [Fe(η-C₅H₅)₂][PF₆], are similar to those of low-spin d⁵ complexes of Cr^I, Mn^II and Fe^III.

Treatment of [Cu(MeCN)₄] BF₄ with 2-(diphenylphosphino)pyridine (dppy) at room temperature in acetonitrile or dichloromethane gives [Cu₂(µ-dppy)₂(MeCN)_x][BF₄]₂, x= 4 or 2, respectively. Reaction with an excess of dppy in refluxing acetone leads to the formation of [Cu₂(µ-dppy)₃]-[BF₄]₂, which gives [Cu(µ-dppy)₃(MeCN)][BF₄]₂ upon recrystallization from acetonitrile. This complex can also be obtained from [Cu(MeCN)₄]BF₄ by reaction with an excess of dppy in refluxing acetonitrile. Substituted complexes [Cu₂(µ-dppy)₃L_x][BF₄]₂[x= 1, L = 2-methylpyridine, x= 2, L = 4-methylpyridine, P(OMe)₃, or PMe₃] are also described. Variable-temperature ¹H and ³¹P-{¹H} n.m.r. studies show that MeCN and dppy dissociation and rapid ligand-exchange processes take place in solution. The crystal structure of [Cu₂(µ-dppy)₃(MeCN)][BF₄]₂ has been determined by X-ray methods. Crystals are monoclinic, space group P2₁/c with Z= 4 in a unit cell of dimensions a= 21.424(7), b= 13.186(6), c= 18.232(6)Å, and β= 99.77(2)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by blockmatrix least squares to R= 0.0657 for 6 539 observed reflections [I 2σ(I)]. The structure consists of [Cu₂(µ-dppy)₃(MeCN)]²⁺ cations and of BF₄ ^– anions. In the cations the two copper atoms are held in close proximity [2.721(3)Å] by three dppy ligands acting as bridges through the P and N atoms. One copper atom is three-co-ordinate, being bonded to two N and one P atom from dppy ligands, the other is four-co-ordinate, being bonded to two P and one N atom from dppy ligands and to an additional N atom from an acetonitrile molecule. As expected, the Cu–P and Cu–N bonds for the three-co-ordinate copper are shorter than these of the four-co-ordinate copper.