[Cu$_{24}$S$_{12}$(PMeiPr$_2$)$_{12}$], [Cu$_{28}$S$_{14}$(PtBu$_2$Me)$_{12}$],[Cu$_{50}$S$_{25}$(PtBu$_2$Me)$_{16}$], [Cu$_{70}$Se$_{35}$(PtBu$_2$Me)$_{21}$], [Cu$_{31}$Se$_{15}$(SeSiMe$_3$)(PtBu$_2$Me)$_{12}$] and [Cu$_{48}$Se$_{24}$(PMe$_2$Ph)$_{20}$]: New Sulfur- and Selenium-Bridged Copper Clusters