Structural Variety within Gallium Diphosphonates Affected by the Organic Linker Length

Abstract

Three new gallium diphosphonates: Ga(3)(OH)(O(3)PC(3)H(6)PO(3))(2) (1), Ga(4)(O(3)PC(5)H(10)PO(3))(3)(C(5)H(5)N)(2) (2), and Ga(HO(3)PC(10)H(20)PO(3)) (3), in which the diphosphonate bridging ligands have 3, 5, and 10 methylene units, respectively, have been synthesized using solvothermal methods and their structures determined using single-crystal laboratory and synchrotron X-ray diffraction data. All three materials contain Ga-centered tetrahedra and octahedra linked together through the -PO(3) groups of the diphosphonate ligands to form two-dimensional pillared slab (1) and three-dimensional pillared (2 and 3) materials. Compound 1 contains bridging hydroxide anions that connect Ga-centered octahedra and tetrahedra, and contains pillared slabs in which one side of the Ga-P-O/OH/CH hybrid layers are connected by the propylenediphosphonate groups only. This slab also contains propylenediphosphonate groups arranged orthogonally to the pillaring direction in the outermost layer of the Ga-P-O/OH/CH hybrid layers. Compound 2 is a framework structure that contains framework pyridine molecules between alternate layers of diphosphonate-pillared Ga-P-O layers and is structurally stable to loss of 1 equiv of pyridine molecules from the structure. Compound 3 is a partially condensed pillared framework structure with one P-O-H bond per diphosphonate group remaining in the resulting material. The structural changes observed as the alkylene chain in the diphosphonate ligand is increased in these compounds is compared to other members of the gallium diphosphonate family synthesized in a similar manner, and other metal diphosphonate series, to gain some general oversight of the structural trends observed in series of metal diphosphonate materials in which the alkylene chain length is varied systematically.

Conventional and Unconventional Metal–Organic Frameworks Based on Phosphonate Ligands: MOFs and UMOFs

“…Attfield and co-workers recently reported a series of gallium alkylbisphosphonates in which they attempted to systematically vary the chain length from n = 3 to n = 10 . The results of their research combined with our own confirm that the structures of these compounds are quite diverse.…”

“…Attfield and co-workers recently reported a series of gallium alkylbisphosphonates in which they attempted to systematically vary the chain length from n = 3 to n = 10. 35 The results of their research combined with our own confirm that the structures of these compounds are quite diverse. However, identical reaction conditions can produce some materials that appear to be capable of isoreticular extension whereas others appear to be limited by the conformation of the ligands.…”

Isoreticular Investigation into the Formation of Four New Zinc Alkylbisphosphonate Families

“…A recent review paper outlined the various work conducted in alkyl(phosphonic acid)-based frameworks . Two main examples stand out that have attempted systematic investigation of these materials with modification of chain length, one by Zubieta and co-workers using vanadium and one by Attfield and co-workers using gallium. , Combining our work with the aforementioned, we can come to the conclusion that these alkylbisphosphonates can vary greatly in structure; however, with careful control over reaction conditions, isoreticular extension is possible. For some frameworks, this conclusion is true regardless of the ligand length; for others, it is limited by the conformation of the ligands due to the odd vs even length.…”

“…The difference between the carboxylates and the phosphonates has been the ability not only to form crystalline materials but also to design bonding models, both of which are significantly easier for carboxylates, and subsequently both being difficult for phosphonates. For phosphonate materials, authors make claims of rational design and structural control, , and no subclass has been more subject to these generalizations than the alkylbisphosphonates. It has in the past been suggested that the chain length determines structural type.…”