In the low-temperature reaction of B10H14 with C5H5N, a new product, identified as arachno-6,6-(C5H5N)(2)B10H12, was formed in high yield and purity. The proposed 6,6-L(2)B(10)H(12) compound represents the first known report of this decaborane substitution pattern. The formation of an asymmetric 6,5-(C5H5N)(2)B10H12 isomer was unexpected on the basis of literature precedent describing the synthesis and structural elucidation of numerous 6,9-L(2)B(10)H(12) species (where L = Lewis base). The observed reaction sequence in the formation of the 6,6-(C5H5N)(2)B10H12 compound proceeded through an initially observed [H . C5H5N](+)[B10H13](-) intermediate. In addition to the formation of the 6,6-isomer, the synthesis of the 6,9-(C5H5N)(2)B10H12 isomer is also reported from the reflux of nido-B10H14 in pyridine. Refluxing the 6,6-(pyridine)(2)B10H12 isomer in pyridine was also found to convert this isomer into the 6,9-isomer. Both isomers were characterized by B-11 NMR, FTIR, UV-vis, mass spectroscopic, and elemental analyses. The structure of the 6,6-isomer was established by 2D B-11-B-11 COSY NMR data and by the first application of a pure phase B-11-B-11 2Q correlation NMR (double-quantum) experiment to the elucidation of a borane cluster framework. This latter NMR technique was very successful in greatly simplifying the NMR assignments of the 6,6-substituted decaborane cluster species and should be a very powerful tool in cluster structure elucidation in general.