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

• Solvent free cesium structures of 1,8-naphthalimide substituted carboxylate ligands.
• Bridging carboxylate oxygen atoms forming rod and 2D sheet structures.
• Hexagonal planar cesium with η2-coordination interactions of naphthalimide rings.
• Cesium cations bridged by η2:η1 interactions from methylene groups in the ligands.
• Supramolecular 3D structure supported by strong π⋯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 π⋯π stacking supramolecular tecton, with cesium hydroxide followed by solvothermal treatment in ethanol led to the formation of crystalline Cs(Lgly) (1) and Cs(Lene) (2), where the Lene− ligand, 2-(1,8-naphthalimido)acrylate, is formed from the dehydration of the HLser starting material. The X-ray studies show that 1 crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 30.430(7) Å, b = 4.9820(12) Å, c = 16.566(4) Å, β = 101.951(4)° and 2 in the monoclinic space group P21/n with unit cell dimensions a = 13.6049(15) Å, b = 6.8100(8) Å, c = 14.4187(16) Å, β = 105.345(2)°. 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 O6-coordination geometry. The latter geometry is stabilized on both sides of the plane by η2-coordination of naphthalimide rings. The 1,8-naphthalimide rings are involved in intra-sheet π⋯π stacking interactions. The O6 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 η2:η1 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 π⋯π interactions. Both complexes show naphthalimide based fluorescence.

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