The largest known zirconium cluster with an idealized formula of [Zr26O18(OH)30(HCOO)38] was obtained via solvolysis of ZrOCl2 in DMF/HCOOH.

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.

Abstract:The new linker molecule 4-phosphono-biphenyl-4 1 -carboxylic acid (H 2 O 3 P-(C 6 H 4 ) 2 -COOH, H 3 BPPA) has been structurally elucidated in hydrogen-bonded networks with the ammonium cation NH 4 (H 2 BPPA)(H 3 BPPA) (1) and the hexaamminecobalt(III) cation [Co(NH 3 ) 6 ](BPPA)¨4H 2 O (2). The protic O-H and N-H hydrogen atoms were found and refined in the low-temperature single-crystal X-ray structures. The hydrogen bonds in both structures are so-called charge-assisted; that is, the H-bond donor and/or acceptor carry positive and/or negative ionic charges, respectively.The H-bonded network in 1 consists of one formally mono-deprotonated 4-phosphonato-biphenyl-4 1 -carboxylic acid group; that is, a H 2 BPPA´anion and a neutral H 3 BPPA molecule, which together form a 3D hydrogen-bonded network. However, an almost symmetric resonance-assisted hydrogen bond (RAHB) bond [O¨¨¨H = 1.17 (3) and 1.26 (3) Å, O¨¨¨H¨¨¨O = 180 (3)˝] signals charge delocalization between the formal H 2 BPPA´anion and the formally neutral H 3 BPPA molecule. Hence, the anion in 1 is better formulated as [H 2 BPPA¨¨¨H¨¨¨H 2 BPPA]´. In the H-bonded network of 2 the 4-phosphonato-biphenyl-4 1 -carboxylic acid is triply deprotonated, BPPA 3´. The [Co(NH 3 ) 6 ] 3+ cation is embedded between H-bond acceptor groups, -COO´and -PO 3´a nd H 2 O molecules. The incorporation of sixteen H 2 O molecules per unit cell makes 2 an analogue of the well-studied guanidinium sulfonate frameworks.

The bifunctional compounds 3,5-dimethyl-4-(4-phosphonophenyl)-1H-pyrazole 1 and 4-(4-phosphonophenyl)-1H-pyrazole 2 were synthesized via Suzuki-Miyaura coupling, starting from a Boc-protected pyrazolylboronic acid ester and the iodoarylphosphonate. The target compounds were isolated after acidic hydrolysis in the form of the hydrochloride salts 1 · HCl and 2 · HCl · H 2 O with a yield of 81% and 86%, respectively. Pd(dppf)Cl 2 was found to be superior to Pd(PPh 3 ) 4 as a catalyst; dry 1,4-dioxane as a solvent, Cs 2 CO 3 as a base, and no co-ligands were the best found conditions. The alternative routes through iodoarylphosphonate of iodoarylpyrazole, with the crucial steps based on the copper-catalyzed coupling with acetylacetone or the Arbuzov reaction were proven inefficient. The structures of the isolated hydrochloride salts 1 · HCl and 2 · HCl · H 2 O feature hydrogenbonded networks involving the chloride anions.