CROWN-ETHER COMPLEXES OF LEAD(II) NITRATE - CRYSTAL-STRUCTURES OF THE 12-CROWN-4, 15-CROWN-5, BENZO-15-CROWN-5 AND 18-CROWN-6 COMPLEXES

The straightforward reaction of common crown ethers with Pb(NO3)2 in CH3CN and CH3OH mixtures has produced several crystalline complexes which have been structurally characterized. Crystallographic analysis reveals the following formulations: [Pb(NO3)(12-crown-4)2][Pb(NO3)3(12-crown-4)] (1), [PbL2][Pb(NO3)3L]2 (L = 15-crown-5 (2) or benzo-15-crown-5 (3)), and [Pb(NO3)2(18-crown-6)] (4). As anticipated the cavity size of 18-crown-6 matches the ionic radius of Pb2+ and the lead ion resides exactly in the center of the crown ether. For all four structures, the Pb-O separations range from 2.645(8)-3.06(1) angstrom (crown ether) and 2.53(1)-2.809(8) angstrom (nitrate). Variations in bond distances are noted relating to differences in coordination number, geometry and ionic charge, however, a lone pair effect is not distinguished. The crystallographic parameters are as follows: 1: monoclinic, P2(1)/c with (at 22-degrees-C) a = 8.237(5), b = 28.464(9), c = 16.331(8) angstrom, beta = 93.77(7)-degrees, D(calc) = 2.07 g cm-3 for Z = 4 formula units, and R = 0.038 utilizing 4596 independent observed (F(o) greater-than-or-equal-to 5-sigma(F(o))) reflections; 2: orthorhombic, Pccn with (at 22-degrees-C) a = 37.462(5), b = 9.586(2), c = 17.378(4) angstrom, and D(calc) = 2.00 g cm-3 for Z = 4 (severe disorder precluded a complete structure determination); 3: triclinic, P1 with (at 22-degrees-C) a = 10.392(2), b = 18.799(6), c = 21.069(8) angstrom, a = 112.11(3), beta = 98.01(2), gamma = 104.32(2)-degrees, D(calc) = 1.92 g cm-3 for Z = 2, and R = 0.052 (8505 reflections); 4: monoclinic, P2(1)/c with (at 22-degrees-C) a = 8.171(8), b = 15.499(9), c = 7.856(8) angstrom, beta = 105.08(7)-degrees, D(calc) = 2.06 g cm-3 for Z = 2 and R = 0.034 (1018 reflections).