Syntheses, structures and properties of group 12 element (Zn, Cd, Hg) coordination polymers with a mixed-functional phosphonate-biphenyl-carboxylate linker

Abstract

The new phosphonate-carboxylate ligand from 4-phosphono-biphenyl-4′-carboxylic acid (H 2 O 3 P-(C 6-H 4) 2-CO 2 H, H 3 BPPA) is based on the rigid biphenyl system and is studied toward the coordination behavior of group 12 elements zinc, cadmium and mercury. The crystalline products from hydrothermal syntheses highlight the versatile and different coordination modes with the (partially) deprotonated H 3 BPPA ligand to give coordination polymeric 3D-[Zn 5 (μ 3-OH) 4 (μ 4-O 3 P-(C 6 H 4) 2-CO 2-μ 2) 2 ] n (5), 2D-[Zn(μ 6-O 3 P-(C 6 H 4) 2-CO 2 H)] n (6), 3D-[Cd 3 (μ 5-O 3 P-(C 6 H 4) 2-CO 2-μ 2)(μ 6-O 3 P-(C 6 H 4) 2-CO 2-μ 3)] n (7) and 2D-[Hg(μ 3-HO 3 P-(C 6-H 4) 2-CO 2 H)] n (8). The cobalt complex, 2D-[Co(μ 4-O 3 P-(C 6 H 4) 2-CO 2 H)] n (9) is isostructural to 6. Through additional classic strong carbonyl O-H⋯O hydrogen bonding the dimensionality of the 2D coordination networks increases to 3D supramolecular frameworks. The carboxy-phosphonate ligand shows five different coordination modes which can be described as μ 4-O 3 P-CO 2-μ 2 (5), μ 6-O 3 P-(6), μ 5-O 3 P-CO 2-μ 2 , μ 5-O 3 P-CO 2-μ 3 (7), and μ 3-O 3 P-(8), that is, the ligand bridges altogether between 3 to 8 metal atoms with the phosphonate group alone connecting already 3 to 6 metal atoms. Layers of metal-oxygen polyhedra are interconnected via the biphenyl linker, which either coordinates metal atoms with both donor groups or the-COOH end forms tail-to-tail hydrogen bonds to create 3D or 2D coordination networks, respectively. In the flat {MO x } layers in 6 and 7 the Zn and Cd metal nodes represent a honeycomb and an mcm net, respectively. The coordination polyhedra of the Cd atoms in compound 7 were analyzed towards a trigonal-prismatic coordination environment. The complexes are hydrolytically very stable due to their hydrothermal preparation from aqueous solution at 180-200°C. The compounds could be stored in water or air for months without apparent decomposition. Compounds 5 and 7, where the ligand is fully deprotonated, start to decompose at ∼400°C. The fluorescence emission spectrum of the ligand, 4, shows an intense peak at 365 nm (λ ex = 316 nm). The fluorescence emission of the metal complexes 5, 7 and 9 is shifted towards larger wavelengths with values of 417 nm, 415 nm and 410 nm, respectively (λ ex = 354 nm for 5, λ ex = 350 nm for 7, λ ex = 400 nm for 8, λ ex = 360 nm for 9). In addition, the crystal structures of the H 3 BPPA ligand precursors 4-iodo-4′-biphenylcarboxylic acid methyl ester, and 4-diethylphosphono-4′-biphenylcarboxylic acid methyl ester are described here for the first time.

Excimer and Red Luminescence Due to Aggregation‐Induced Emission in Naphthalene Based Zinc Phosphonate

“…These chains are interconnected through PO 3 C tetrahedrons along c : each ZnO 4 tetrahedron shares two apices with two PO 3 C tetrahedrons and two other apices with four polyhedrons (two PO 3 C and two ZnO 4 tetrahedrons) (Figure S3c). Compared with other phosphonates containing a metal ion with a tetrahedral coordination, and to Zn‐phosphonate containing conjugated molecules or ligands, this layered structure is unique, due to the fact that strong infinite “Zn–O–Zn” and “Zn–O–P–O–Zn” ionocovalent bonds are observed along b and along b and c , respectively, within the inorganic layers.…”

“…Zinc phosphonates containing aryl moieties may provide a potential source for the realization of luminescent materials, since Zn 2+ , due to its d 10 electronic configuration, does not quench the fluorescence emission of aromatic rings. Nevertheless, the number of zinc phosphonates containing conjugated molecules or ligands that show PL properties is rather limited, and the relative role of each partner in this type of material (zinc or organic ligands) or the structural features (chemical bonding, etc.) is still a matter of debate.…”

Charge-Assisted Hydrogen-Bonded Networks of NH4+ and [Co(NH3)6]3+ with the New Linker Anion of 4-Phosphono-Biphenyl-4′-Carboxylic Acid

“…Diffractograms were obtained on flat layer sample holders with a beam scattering protection blade installed, which led to the low relative intensities measured at 2θ < 7˝. Details of the synthesis of 4-phosphono-biphenyl-4 1 -carboxylic acid (H 2 O 3 P-(C 6 H 4 ) 2 -COOH, H 3 BPPA) will be given elsewhere [62]. …”

Fluorenyl Zinc Phosphonate Zn(H2O)PO3-C13H9·H2O: Hybrid Columnar Structure with Strong C-H···π Interactions

“…Metal phosphonates were reported for the first time almost forty years ago by Alberti et al opening the route to the discovery of hundreds of compounds with an extremely rich chemistry (see for a review) and covering a wide range of applications, such as biotechnology, catalysis, gas storage, and photoluminescence , . In contrast, the number of zinc phosphonates containing conjugated molecules or ligands, which show PL properties is quite limited. These compounds are either phosphono‐biphenyl carboxylates, or triazine‐based phosphonates, or contain terephthalate linkers, naphthyl groups, phenyl‐sulfonyl groups or pyrazine groups, or even more simply benzyl groups .…”

“…In contrast, the number of zinc phosphonates containing conjugated molecules or ligands, which show PL properties is quite limited. These compounds are either phosphono‐biphenyl carboxylates, or triazine‐based phosphonates, or contain terephthalate linkers, naphthyl groups, phenyl‐sulfonyl groups or pyrazine groups, or even more simply benzyl groups . The primordial role of the organic ligand, especially the π–π stacking, and the C–H ··· π interactions in the PL properties of these phosphonates has been emphasized by most of the authors, whereas in contrast the role of the 3d 10 zinc cation is still not elucidated and requires further investigation as suggested for the phenyl phosphonate Zn(O 3 PC 6 H 5 ) · H 2 O …”