Metallacrown ether complexes of the type PtCl2(Ph2P(CH2CH2O)nCH2CH2PPh2} (n = 3-5) have been prepared and characterized by 13C and 31P NMR spectroscopy. A single complex is formed with the n = 3 and 4 ligands, and one major and two minor complexes are formed with the n = 5 ligand. X-ray crystal structures of the n = 4 and major n = 5 complexes have been obtained (n = 4: monoclinic space group P21/n; a = 12.798 (1), b = 16.4875 (9), c = 16.726 (1) Å β = 104.003 (6)° V = 3424.4 Å3; Z = 4. n = 5: monoclinic space group P21/c; a = 12.9220 (9), b = 15.5925 (8), c = 18.3271 (5) Å β = 92.540 (5)°, V= 3689.0 Å3; Z = 4). The metallacrown ether rings in both complexes exhibit similar conformations. The cavity in the n = 4 complex appears to be of the appropriate size for binding Li+ and that in the n = 5 complex appears to be of the appropriate size for binding Na+. The complexes do appear to coordinate alkali metal cations, but these reactions are complicated by solubility differences and by loss of the chlorides. The n = 4 complex reacts with AgBF4 to yield the cationic [Pt(Ph2P(CH2CH2O)4CH2CH2PPh2-P, P', O)(H2O)](BF4)2 complex. The X-ray crystal structure of this complex has been determined (triclinic space group Pi; a = 9.971 (2), b = 10.293 (2), c = 20.212 (5) Å; α = 80.92 (2), β = 84.92 (2), γ = 75.48 (1)° V = 1980.3 Å3; Z = 2). The Ph2P(CH2CH2O)4CH2CH2PPh2 ligand is coordinated to the platinum through both phosphines and one ether oxygen and is also hydrogen bonded to the platinum-coordinated water through two other ether oxygens. © 1992, American Chemical Society. All rights reserved.