Molybdenum Bisphosphonates with Cr(III) or Mn(III) Ions

The synthesis of Mo-VI bisphosphonates (BPs) complexes in the presence of a heterometallic element has been studied. Two different BPs have been used, the alendronate ligand, [O3PC(C3H6NH3)(O)PO3](4-) (Ale) and a new BP derivative with a pyridine ring linked to the amino group, [O3PC(C3H6NH2CH2C5H4N)(O)PO3](4-) (AlePy). Three compounds have been isolated, a tetranuclear Mo-VI complex with Cr-III ions, (NH4)(5)[(Mo2O6)(2)(O3PC(C3H6NH3)(O)PO3)(2)Cr]center dot 11H(2)O (Mo-4(Ale)(2)Cr), its Mn-III analogue, (NH4)(4.5)Na-0.5[(Mo2O6)(2)(O3PC(C3H6NH3)(O)PO3)(2)Mn]center dot 9H(2)O (Mo-4(Ale)(2)Mn), and a cocrystal of two polyoxomolybdates, (NH4)(10)Na-3[(Mo2O6)(2)(O3PC(C3H6NH2CH2C5H4N)(O)PO3)(2)Cr](2)[CrMo6(OH)(6)O-18]center dot 37H(2)O ([Mo-4(AlePy)(2)Cr](2)[CrMo6]). In this latter compound an Anderson-type POM [CrMo6(OH)(6)O-18](3-) is sandwiched between two tetranuclear Mo-VI complexes with AlePy ligands. The protonated triply bridging oxygen atoms bound to the central Cr-III ion of the Anderson anion develop strong hydrogen bonding interactions with the oxygen atoms of the bisphosphonate complexes. The UV-Vis spectra confirm the coexistence in solution of both POMs. Cyclic voltammetry experiments have been performed, showing the reduction of the Mo centers. In strong contrast with the reported Mo-VI BP systems, the presence of trivalent cations in close proximity to the Mo-VI centers dramatically impact the potential solid-state photochromic properties of these compounds.