The structural characterization of the "magnesylamine" compound [(Et(2)O)Mg(Cl){N(SiMe(3))(2)}](2), 1, and the novel species Mg{N(SiMePh(2))(2)}(2), 2, by X-ray crystallography is described. The structure of 1 features dimeric molecules with two four-coordinate magnesium centers. Each magnesium is coordinated in a distorted tetrahedral fashion by terminally bound -N(SiMe(3))(2) and Et(2)O ligands and by two symmetrically bridging chlorides. It represents the first such data for a magnesylamine species of the general formula R(2)NMgX.n ether (R = alkyl, aryl, or related group; X = halide). The structure of 2 is composed of monomeric molecules with the magnesium bonded to two terminal amide groups with an average Mg-N bond length of 1.966(6) Angstrom. The 2-fold coordination at the magnesium is distorted from linearity, and an N-Mg-N angle of 162.8(3)degrees is observed. This structure is the first for a magnesium bis(amide) of formula Mg(NR(2))(2) (R = alkyl, aryl, or related group) in the solid state. The deviation from linear geometry is attributed to weak Mg-aromatic ring interactions. Crystal data for 1 (Mo K alpha, lambda = 0.710 69 Angstrom) or 2 (Cu K alpha, lambda = 1.541 78 Angstrom) at 130 K : 1, a 10.483(2) Angstrom, b = 13.558(3) Angstrom, c = 13.133(4) Angstrom, beta = 104.04(2)degrees, V = 1810.8(8) Angstrom(3), space group P2(1)/c, Z = 2,2753 (I > 3 sigma(I)) data, R = 0.052; 2, a = 10.951(2) Angstrom, b = 15.350(2) Angstrom, c = 26.890(5) Angstrom,beta = 91.92(2)degrees V = 4517.2(15) Angstrom(3), space group P2(1)/c, Z = 4, 3611 (I > 2 sigma(I)) data, R = 0.069.