Ten-vertex [6,6-(PMe2Ph)2-arachno-6-PdB9H12-9-(PMe2Ph)] 1a and eleven-vertex [7,7-(PMe2Ph)2-nido-7-PdB10H12] 2a have been isolated as occasional by-products from an extension to palladaborane chemistry of the one-pot route for the preparation of the nine-vertex platinaborane [(PMe2Ph)2PtB8H12] 3b from [PtCl2(PMe2Ph)2] and B10H14, but using [PdCl2(PMe2Ph)2] instead of [PtCl2(PMe2Ph)2] to generate [4,4-(PMe2Ph)2-arachno-4-PdB8H12] 3a in yields of upto 75%. The two by-products 1a and 2a are each characterized by single-crystal X-ray diffraction analysis. Space group and cell parameters are as follows: for 1a, triclinic, $$P\bar 1 $$ , a = 10.1139(2) Å, b = 10.3955(2) Å, c = 31.5086(7) Å, α = 94.4720(12)°, β = 91.6420(10)°, and γ = 105.3790(11)°; for 2a, monoclinic, P21/n, a = 14.6059(3) Å, b = 10.9988(2) Å, c = 15.1516(3) Å, and β = 93.0000(14)°. Whereas 1a and 1b are isomorphous, Compounds 2a and 2b are not, and show significant differences in intramolecular conformation.