Zeolites and related molecular sieves, which contain rigid frameworks and accessible internal channels and/or cages, have been dominating the porous material world for a long time, because of their widespread applications in catalytic and separation science.[1,2] Although there is an increasing demand for materials with tunable structures, the structural design of zeolites is limited by their requirement for If one Si atom causes pyramidalization, two of them should enhance the effect. We have calculated the Si2BH5 structure at various levels and found it to have a Cs structure (7) with a pyramidal boron atom. The corresponding C2v structure (8) with a planar boron center is found to be higher in energy. The calculated value of q is larger than that of 1. The energy differences are also found to be considerably higher (Table 5). The heavier group 14 elements, Ge and Sn, must also influence the pyramidalization of boron. Calculations at the B3LYP/LANL2DZ level show that q decreases as Si (14.18) is replaced by Ge (7.78) or Sn (6.58 ; Table 6). However, the inversion barrier increases in going from Si (0.7) to Ge (7.5) to Sn (12.7 kcalmol 1). The unexpected nonplanar arrangement of the tricoordinate boron center in 1 provides another demonstration of the many novel structural patterns that the heavier elements of the main group can contribute to the firstrow elements, and invites experimental verification.