Cesium complexes of naphthalimide substituted carboxylate ligands: Unusual geometries and extensive cation-π interactions

The reactions of (1,8-naphthalimido)ethanoic acid (HLgly), and (S)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (HLser), protonated forms of ligands that contain a carboxylate donor group and a 1,8-naphthalimide pi. . .pi stacking supramolecular tecton, with cesium hydroxide followed by solvothermal treatment in ethanol led to the formation of crystalline Cs(L-gly) (1) and Cs(L-ene) (2), where the L-ene(-) ligand, 2-(1,8-naphthalimido)acrylate, is formed from the dehydration of the User starting material. The X-ray studies show that I crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 30.430(7) angstrom, b = 4.9820(12) angstrom, c = 16.566(4) angstrom, beta = 101.951(4)degrees and 2 in the monoclinic space group P2(1)/n with unit cell dimensions a = 13.6049(15) angstrom, b = 6.8100(8) angstrom, c = 14.4187(16) angstrom, beta = 105.345(2)degrees. The solid state structure of 1 contains two types of 6-coordinate cesium cations linked into sheets by bridging carboxylate oxygen atoms. One cation has a distorted octahedral environment, while the other is in an unusual planar, hexagonal O-6-coordination geometry. The latter geometry is stabilized on both sides of the plane by eta(2)-coordination of naphthalimide rings. The 1,8-naphthalimide rings are involved in intra-sheet pi. . .pi stacking interactions. The O-6 coordination sphere of complex 2 is distorted and only half-filled with the oxygen atoms, which link the cations into rods that are further linked into sheets by bridging interactions of naphthalimide carbonyls with cesium cations from adjacent rods. The open face on the cation has unique eta(2):eta(1) interactions with two methylene groups in the ligands. These sheets are linked into a 3D supramolecular structure by interdigitated 1,8-naphthalimide rings involved in strong pi. . .pi interactions. Both complexes show naphthalimide based fluorescence. (C) 2015 Elsevier B.V. All rights reserved.