An x-ray diffraction study of the crystal structure of Cu2B10H10 shows that the earlier proposal that the B10H10—2 ion has D4d symmetry is correct, and further establishes the covalent nature of the interactions of CuI with B atoms forming the edges of the polyhedron. There are eight Cu2B10H10 in a unit cell having dimensions a = 10.11, b = 11.36, and c = 14.50, and the space group is Pcab. Bonds within a tetragonal pyramid are 1.73 Å (to apex) and 1.86 Å (along base), while B–B bonds between the tetragonal pyramids are 1.81 Å in length. The closest Cu···B distances range from 2.14 to 2.33 Å in length.

Recent studies have extended the chemical principles' of boron hydrides to include boron-boron bonds between polyhedra or polyhedral fragments2 and rearrangements3 4 of boron frameworks. We report here results, suggesting new areas of research, including a condensation reaction to form B20H18-' from BioH,0-o, a substitution reaction on BioH,0-2 to form BoH90H-2, a suggestion of polyhedral isomerization, the presence of essentially covalent metal bonds to B in BloH1o-2, and a new type of free radical.The B2,H18-2 Ion.-Reaction of dilute aqueous BloHio(HNEt3)2 solutions with 1eCl3 yields nearly white crystals of B2eH,8(HNEt3)2, insoluble in cold water but soluble in several polar organic solvents, melting with decomposition at 175-1740C, and having a density of 0.941 gm cm-3. The rough molecular weight of 420 from the vapor pressure depression of CH30H solutions allowed the number of molecules per unit cell of the crystal to be fixed at two and led to the crystallographically determined molecular weight of 437 i: 2 in agreement with the expected value of 439. Moreover, the ion is centrosymmetric, since the space group is P21/a. The B1' nuclear magnetic resonance (NMR) spectrum ( Fig. 1) is related to that2 of BcH10-' in a way which suggests that one apex' B atom and one equatorial B atom of each Bo unit are involved in the formation of B20H18-. The only structure' consistent with the present valence theory is now being tested by X-ray diffraction methods in this laboratory. The ultraviolet spectrum has intense bands at 293 and 230 my, neither of which is present in the BoHlo -2 spectrum in noticeable intensity.The chemical reaction 2B0oH10-2 + 4Fe+3 B20H18-2 + 4Fe+2 + 2H+ goes to 95 per cent yield in aqueous solution with slight excess of Fe +3. Analytical results for the HNEt3+ salt and the NMe4+ salt (mp > 300°C) are shown in Table 1.The BoH9OH-2 Ion.-A quantitative reaction of B2oH18(HNEt3)2 with aqueous base, B2oH18(HNEt3)2 + 40H -> 2BXH9OH-2 + 2NEt3 + 2H20, establishes a substituted BHio -2 ion. The salt K2B,,HOH 2H20 loses water at room temperature to form a stable monohydrate (Table 1) but is stable as high as 300°C except for further loss of H20. The BioHO9H-2 ion may be the same as that prepared by quite different methods by Knoth et al.,5 whose research we became aware of after completion of our own. Polyhedral Isomerization.-Upon initial deuteration in strong acid, BioHlo-is apex5 substituted. Also, when freshly prepared, BioH90H-2 is apex substituted.The large high field doublet, initially like7 that in BioH1o , of the B"1 NMR spectrum becomes unsymmetrical after a few hours at room temperature, thus suggesting an apparent partial migration of the substituent. A probable transformation process is shown in Figure 2. If this process is more general, it may occur in B12HIOX2-2, where two X atoms on adjacent B atoms may wander to nonadjacent 729

Methods for the solution of three-dimensional crystal structures from the three-dimensional Patterson function have been further developed by use of (a) the Symmetry Minimum Function which is based upon all symmetry interactions (e.g. :Harker lines and planes), (b) a simultaneous high order superposition function which makes use of all the symmetry of the space group, and (c) a combined high order superposition function in which the Symmetry Minimum Function is included to reduce the number of spurious peaks. These functions introduce a more direct method for the analysis of somewhat more complex structures than methods which have previously been described.

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A single-crystal three-dimensional x-ray diffraction study has established the chemical composition and molecular structure of B20H16, which has D2d symmetry. Two B10H14 cages are joined together at the open faces, with the loss of all bridge H atoms, and loss of terminal H atoms on the four B atoms which join these cages. There are eight molecules in the tetragonal unit cell which has dimensions of a=9.650 and c=29.64 Å. The space group is I41/acd, and the molecules occupy sites of symmetry S4.