Cu—S distance

The interatomic distances found are V—S = 2.186 0.040 A and Cu—S — 2.285 i 0.014 A. The Cu—S distance is somewhat smaller than the sum of the tetrahedral radii2) for sulfur and univalent copper, 2.39 A. As in the case of chalcopyrite, this probably indicates that the valence states are not well defined as CuIiVvSi, but fluctuate, the copper resonating between cuprous and cupric states and the vanadium between quinquivalent and lower states. 

Structure type LaCuPbSa (Brermarr arrd Ibers, 1992) (Figure 103, Table 53). SG Pnma, Z = A, a = 0.8091, b = 0.4093, c = 1.5996 nm. The rarrdomly distributed La and Pb atoms (M) are located in monocapped trigonal prisms formed by the S atoms. The shortest M-S distance is 0.2864 run. The sulfur atoms create a tetrahedral arrangement around the single independent copper atom, and the shortest Cu-S distance is 0.2334 run. 

Rusticyanin has a high reduction potential (680 mV), which is similar to that for the Type 1 Cu center in fungal as opposed to tree laccase (785 mV) (73). This trend is so far unexplained. From the sequence and EXAFS studies, His-Cys-His-Met coordination is a reasonable possibility for rusticyanin (55). It may well be that the reduction potential is determined by effects of a polypeptide backbone on Cu—S(Cys) and Cu—S(Met) bond distances and the Cu ligand field (74). If this is the case, however, rusticyanin would be expected to have one or both Cu—S distances shorter than in other blue copper proteins, which is not borne out by information from EXAFS (Table IV). A further possibility that the Cu(I) form is three-coordinate, as in the case of plasto-cyanin at low pH (Fig. 2), has no strong support at present (75). 

Even if the evolution is less spectacular, the spectra at copper edge confirm that dehydration induces the onset of disorder. In particular, the fourth peak at about 4A in Fig. 22 a attributable to the Cu—S distances within the stack ofCuS4 units (Fig. 20) shifts towards longer distances in the 3 H2O compound. This may be attributed to a disorder within these stacks. Once more no ordered bringing together of metallic ions belonging to different chains is observed. 

The calculated Mn—S distances are close to (although slightly larger than) the corresponding distance (2.60 A) found in MnPSj but the Cu—S distances are abnormally short compared to values estimated from the literature on Cu(I)-sulfur compound Finally, the P—S bond length agrees with the values usually encountered in the MPS3 family. 

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