The new cyclic silanes [(C5H3N)(CH2O)(2)SiMe(2)](2) (1) and (C5H3N)(CH(2)CPh(2)O)(2)SiMe(2) (2) containing 16-membered and 10-membered rings, respectively, were prepared by the condensation reaction of Me(2)SiCl(2) with an appropriate pyridine diol in the presence of Et(3)N. X-ray studies show that the dimeric formulation for 1 represents a tetracoordinate cyclic silane, whereas 2 has a geometry halfway from a tetrahedron toward a trigonal bipyramid (TBP) as a result of Si-N-ax donor action. Si-29 and H-1 NMR indicate retention of the coordination geometry for 2 in solution that undergoes rapid Si-N cleavage and ring rearrangement. In comparison with other silanes containing five- and six-membered rings that exhibit nitrogen or oxygen coordination, the presence of larger rings, as in 2 and related silanes having sulfur coordination, indicates that retention of donor action persists, thus largely ruling out ring size as a dominant factor controlling the possibility of donor action at silicon. The dimeric silane 1 crystallizes in the triclinic space group P (1) over bar with a = 6.347(3) Angstrom, b = 12.455(4) Angstrom, c = 14.289(5) Angstrom, alpha = 101.63(3)degrees, beta = 102.99(3)degrees, gamma = 104.71(3)degrees, and Z = 2. The cyclic silane 2 crystallizes in the triclinic space group P (1) over bar with a = 9.733(4) Angstrom, b = 10.938(2) Angstrom, 14.312(3) Angstrom, alpha 89.03(2)degrees, beta = 74.59(3)degrees, gamma = 79.24(3)degrees, and Z = 2. The final conventional unweighted residuals are 0.040 (1) and 0.039 (2).