Synthesis and nuclear magnetic resonance study of the auranonaborane and diauradecaborane arachno-type compounds, [4-(S2CNEt2)-arachno-4-AuB8H12] and [6,9-(S2CNEt2)2-arachno-6,9-Au2B8H10]; crystal and molecular structure of [6,9-(S2CNEt2)2-arachno-6,