 If the central carbon were to be tetrahedral, it would have the form of spiropentadiene, but with additional bonds between the two cyclopropyl rings rather than double-bonds within them.The analogous germa- and stannapyramidanes, with trimethylsilyl groups bonded to the corners, Ge[C4(SiMe3)4] and Sn[C4(SiMe3)4] on the other hand have been synthesised.These adopt a square pyramidal geometry analogous to the trigonal pyramid of tetrahedrane, with the germanium or tin atom at the vertex.