Novel building units in the construction of materials of the oxomolybdate–organodiphosphonate/copper(II)–dipodal-organonitrogen ligand system: Structural influences of dipodal ligand tether length and flexibility

The hydrothermal reactions of copper(II) acetate, MoO3, 1,4-butylenediphosphonic acid and a ligand of the N,N,N′,N′-tetrakis(pyridine-2-ylmethyl)alkyl-α,ω-diamine (Ln, where n is the number of methylene groups) in the presence of HF provided crystals of [{Cu2(L7)(H2O)2}Mo5O15{O3P(CH2)4PO3}]·2H2O (1·2H2O) and [{Cu2(L5)}Mo6O18(H2O){O3P(CH2)4PO3}]·14H2O (2·14H2O). Compound 1 contains the common pentanuclear cluster building block {Mo5O15(O3PR)2}4−, extending into one-dimensional chains through the alkyl tethers of the diphosphonate ligand. Each pentanuclear subunit bonds to four copper(II) sites of the {Cu2(L7)(H2O2)}4+ subunits that serve to link each chain to five adjacent chains to propagate the structure in three dimensions. The Cu/Mo/P/O inorganic substructure which arises from this juxtaposition of building motifs is a one-dimensional {Cu2Mo5O15(O3P−)2} unit consisting of clusters linked through Cu(II) sites. The alkyl arms of the diphosphonate and nitrogen ligands radiate outward to link to adjacent chains and propagate the structure in three-dimensions. In contrast, compound 2 exhibits a hexanuclear building unit {Mo6O18(H2O)(O3P−)2}4−, which again extends into a chain through the tethering diphosphonate ligands. Each cluster bonds to four Cu(II) centers to generate one-dimensional inorganic substructures of the type {Cu2Mo6O18(H2O)(O3P−)2}n. In contrast to 1, the {Cu2(L5)}4+ subunits of 2 associate with a single chain, rather than radiating outward to link to adjacent chains. Consequently, the three-dimensional expansion is effected through the diphosphonate tethers.