Cadmium() carboxyphosphonates based on mixed ligands: syntheses, crystal structures and recognition properties toward amino acids

Three novel cadmium( ii ) carboxyphosphonates with three-dimensional (3D) frameworks and supramolecular structures, namely, Cd 3 [(L) 2 (1,10-phen) 1.5 ]·H 2 O ( 1 ), Cd[(L′)(H 2 biim)] ( 2 ), and Cd[(L′)(H 2 biim)(H 2 O)]·H 2 O ( 3 ) (L = OOC-C 6 H 4 -CH 2 PO 3 , L′ = OOC-C 6 H 4 -CH 2 PO 2 (OC 2 H 5 ), 1,10-phen = 1,10-phenanthroline, H 2 biim = 2,2′-biimidazole), were synthesized under hydrothermal conditions and were structurally characterized. For compound 1 , the Cd(1)O 6 , Cd(2)O 4 N 2 , Cd(3)O 2 N 2 , Cd(4)O 4 and CPO 3 polyhedra were interconnected in a one-dimensional (1D) chain along the b -axis via corner- and edge-sharing. The adjacent chains were connected with each other by sharing the L 3− anions, giving rise to a 3D framework structure. Compound 2 adopted a 3D supramolecular structure. The interconnection of two Cd(1)O 4 N 2 polyhedra and two CPO 3 tetrahedra via corner-sharing formed a structure unit, with such units further connected in the bc -plane by sharing the L′ 2− anions to exhibit a 2D layer, and then the neighboring layers were further assembled into a 3D supramolecular structure by π-π stacking interactions. In compound 3 , the Cd(1)O 4 N 2 and CPO 3 polyhedra were interconnected to form a unit, and then the interconnection of multi-units were assembled into two kinds of 1D chains, whereby chains and other chains are further connected by π-π stacking interactions to present a 3D supramolecular structure. The luminescence properties of compounds 1-3 were investigated. Meanwhile, the excellent abilities of compounds 2 and 3 for the selective recognition of tryptophan (Trp) were demonstrated. Three novel cadmium( ii ) carboxyphosphonates have been hydrothermally synthesized. The luminescence properties of compounds 1-3 have been investigated. Meanwhile, the excellent abilities of compounds 2 and 3 for selective recognition of tryptophan (Trp) have been demonstrated.