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Preliminary results of an extended X-ray absorption fine structure (e.x.a.f.s.) and X-ray absorption near edge structure study of jack bean urease have recently been reported [Hasnain & Piggott (1983) Biochem. Biophys. Res. Commun. 112, 279]. These results indicate that the environment of the nickel ion in the enzyme is similar to that in the model compounds Ni(L)2(L')1(ClO4)1 (where L is 1-n-propyl-2-alpha-hydroxybenzylbenzimidazole and L' is the deprotonated form) and Ni(HMB)3(Br)2 (where HMB is 2-hydroxymethylbenzimidazole), the closest similarity being with Ni(L)2-(L')1(ClO4)1. A detailed e.x.a.f.s. analysis has now been carried out and the crystal structures of the two model compounds solved. These results are reported here.

As part of our work on the chemistry of the heavier members of group 13, we recently synthesized and structurally characterized [ bis(hydroboratotris(3,5-dimethylpyrazolyl)}indium(III)]iodide (2) and [bis(methylgallatotris(pyrazolyl))indium(III)]- [In141 (3).1 Recognizing the formal analogy between the hydroboratotrispyrazolyl anion HB(Pz)3-(and its pyrazolylsubstituted derivatives) and the cyclopentadienyl anions C5R5-(R = H, CH3),2 we were led to claim 2 and 3 as analogues of the unknown "indocene" cations [$-(C5R5)2In]+. A characteristic of the cyclopentadienyl anions is their ability to stabilize metals in low oxidation states, e.g., In(CsH5)3and the recently synthesized Ga(C5H5)4 and A14(C~R5)4.5 It seemed to us that synthesis of an In1 complex with HB(Pz")~-(Pz" = a substituted pyrazole) would strengthen the analogy between hydroboratotris(pyrazoly1) anions and cyclopentadienyl anions and also significantly extend the chemistry of In a previous study, we observed thegradual disproportionation of In1 to In111 and In in the presence of HB(PZ*)~-(Pz* = 3,s-dimethylpyrazole) on slowly raising the temperatureofthe reactantsfrom-30 OC to ambient.' We argued that use of a more sterically hindered pyrazole than Pz* might facilitate the isolation of a stable In1 species. On reacting indium iodide with HB(Pz**),-(Pz** = 3-phenylpyrazole) in tetrahydrofuran at -50 OC, we were able to isolate colorless, blocklike crystals. The mass spectra, lH and 13C N M R spectra, and elemental analyses indicated these crystals to be [I~-(HB(Pz**)~)] (1). This was confirmed by an X-ray structural study.'The structure of 1 is shown in Figure l a and b, and comparisons between it and related compounds are shown in Table 1. Whereas the geometry about the metal in 2 and particularly 3 is very close tooctahedral, in 1 the In adopts a pyramidal geometry with respect to the coordinated nitrogen atoms. This arrangement is also seen in 5. The In-N distance in 1 is longer than the corresponding distances in 2 and 3, as expected, and exceeds the sum of the covalent radii by about 8%. There is no In-In interaction in 1, the closest contacts being 6.5 A. The In-In distance in In(CSH5) ( 1 ) Frazer, A.; Piggott, B.; Harman, M.; Mazid, M.; Hursthouse, M. B. A, a = fi = 90°; y = 120°, V = 1255.66 A', and Z = 2(d,ld= 1.471 gmcm-'),p(MoKa) =9.353cm-';absorptioncorrection DIFABS; 5963 reflections, 1910 unique; 1837 with Fo > 3u(F0) were used in the refinement; R = 2.6, R, = 3.5. (8) Cowley, A. H.; Carrano, C. J.; Geerts, R. L.; Jones, R. A.; Nunn, C. M. Angew. Chem., Ini. Ed. Engl. 1988, 27, 277-278. (9) Cowley,A.H.;Geerts, R.L.;Nunn,C.M.;Trofimenko,S.J. Organomet. Chem. 1989, 365, 19-22.U Figure 1. (a, top) Structureof hydroboratotris(3-phenylpyrazolyl)indium, showing the atom-labeling scheme. (b, bottom) Hydridoboratotris(3-phenylpyrazoly1)indium viewed down the 3-fold axis.Table 1. Selected Bond Lengths and Angles for 1 and Related Compounds compd In-N distance (A) N-In-N angle (deg) 1 2.430(4) 78.2(2) 2 2.225(5) 94.6(2), 85.4(2) 2.273(5) 96.1(2), 8...

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Extended X-ray absorption fine structure (EXAFS) spectra at the Cu K-edge have been recorded of the oxidized and reduced form at pH 3.5 of rusticyanin, the type-l or 'blue'-copper protein from Thio6acillusferrooxidans. The EXAFS of oxidized rusticyanin is well simulated with models assuming a ligand set of 2 N(His) and 1 S(Cys) at 1.99 and 2.16 A, respectively. Upon reduction, the average Cu-N ligand distance increases by approx. 0.08A. For both redox states studied, the fit by the simulation is significantly improved by including a contribution of an additional sulfur ligand at approx. 2.8 A. From comparison with structural data of other blue-copper proteins, it is concluded that the copper coordination environment is relatively rigid, which may be a clue to its high redox potential.