Crystal structures of bis(5,6-dihydro-1,4-dithiin-2,3-dithiolato)gold and tetrabutylammonium bis(5,6-dihydro-1,4-dithiin-2,3-dithiolato)nickelate(1-) and the ligandlike character of the isoelectronic radicals [Au(DDDT)2]0 and [Ni(DDDT)2]-