The new monomeric azaaluminatrane Al(tert-BuMe(2)SiNCH(2)CH(2))(3)N, 6, was prepared by the reaction of [Al(NMe(2))(3)](2), 7, and (tert-BuMe(2)SiNHCH(2)CH(2))(3)N, 11, and was characterized by H-1, C-13, Al-27, and Si-29 NMR, and IR spectroscopies and mass spectrometry. Its analogue Al(Me(3)SiNCH(2)CH(2))3N, 3, was structurally characterized and shown to contain a trigonal monopyramidal aluminum center. The dimeric azaaluminatrane [Al(Me(3)SiNCH(2)CH(2))(2)(HNCH2CH2)N](2), 5, possesses an unusual cis configuration of the central four-membered ring, and the aluminum atoms display a distorted trigonal bipyramidal coordination sphere. Crystal data : 3, a = 13.503(5) Angstrom, b = 10.621(4) Angstrom, c = 17.840(6) Angstrom, beta = 93.29(3)degrees, V = 2554(2) Angstrom(3), Z = 4, space group P2(1)/c, R = 5.2%; 5, a = 12.134(3) Angstrom, b = 17.049(4) Angstrom, c = 18.297(5) Angstrom, beta = 100.02(2)degrees, V = 3726(2) Angstrom 3, Z = 4, space group P2(1)/n, R = 4.6%. Al-27 NMR chemical shifts for a series of Al-N compounds with aluminum coordination numbers ranging from three to six show increased shielding with increasing coordination number.