Photochemistry of dithiocarbamate complexes of Ni(IV). II. Mechanism of photochromic transformations

A study of the soft X-ray photoreduction of [NiIV(S2CNEt2)3][BF4] and soft X-ray photoisomerisation of [PPh4][NiII(S2COEt)3] at the Ni L-edge †

“…47 A previously soft X-ray irradiated sample of [Ni IV (S 2 CNEt 2 ) 3 ][BF 4 ] showing a considerable extent of photoreduction was left in the dark (both visible and soft X-ray) for ca. 1 h. Subsequent scanning over the Ni L-edge at the same sample position showed no detectable reversion to the Ni IV state, implying the absence of the so-called 'dark reaction' previously observed when the dark colour of the Ni IV species returned to give a product spectroscopically identical to the starting material when the acetonitrile, ethanol and methanol solutions 47, 48 and solid PMMA matrices 48 were left in the dark. However, it should be noted that no such 'dark reaction' was reported when frozen methanol matrices were used.…”

“…This was interpreted to imply that the photochemical processes were occurring in an excited triplet state rather than in a singlet state. 47,48 To assess the effect of photon flux, spectra of [Ni IV (S 2 -CNEt 2 ) 3 ][BF 4 ] were recorded just before and directly after a fresh electron beam was introduced into the storage ring. This was the only practical means of reducing the total flux whilst maintaining the same spot size and resolution, as both of these would be affected by a change in the position of the exit slits.…”

“…47,48 In solution,[Ni IV -(S 2 CNR 2 ) 3 ]Br (R = n Bu,42,47,48 CH 2 Ph 45 ) have been shown to be photoreduced to [Ni II (S 2 CNR 2 ) 2 ], NiBr 2 and the corresponding thiuramdisulfide (tds), with a dark reaction resulting in the re-formation of [Ni IV (S 2 CNR 2 ) 3…”