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261spectively. The boron atom for each of these BF4-groups was placed at coordinates calculated by averaging the corresponding fluorine coordinates. These coordinates were not refined but were recalculated periodically (final boron-boron separation = 0.50 A). The isotropic temperature factors for the boron atoms were refined. The populations for the groups refined to final values of 0.71 and 0.29.The final refinement of the structure was done by block-diagonal least-squares with two matrices. All nonhydrogen positional parameters were included in one matrix; the second contained all nonhydrogen thermal parameters, the BF4-population factor, and the scale factor. No reflections were omitted from this refinement. The final R was 0.051 for the 665 reflections with F:

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