Quo vadis niobium? Divergent coordination behavior of early-transition metals towards MOF-5

Abstract

Despite its prevalence, cation exchange is not the only immobilization pathway for foreign cations in the epochal MOF-5 metal–organic framework.

New Solids in As-O-Mo, As(P)-O-Mo(W) and As(P)-O-Nb(W) Systems That Exhibit Nonlinear Optical Properties

“…Thus, in the case of the compound 1, a broad signal with g = 1.643, which is typical for coupled isotropic Nb(IV) ions, was recorded ( Figure 3 ). The observed spectrum is in line with other data for magnetically coupled Nb(IV) centers in the EPR spectra [ 49 , 50 , 51 ].…”

Two-dimensional, conductive niobium and molybdenum metal–organic frameworks

“…The rising edge energy for 1-Nb is 18999.6(2) eV, between the rising edge energies of NbCl 4 (THF) 2 and NbO 2 , while the rising edge energy of 2-Mo is 20015.3(2) eV, higher than the rising edge energies of both MoCl 4 (CH 3 CN) 2 and MoO 2 . 36 , 55 Because rising edge energies are highly dependent on the nature of the coordinated ligands, and because of the lack of molecular analogues for 1-Nb and 2-Mo with well-characterized oxidation states, absolute oxidation state assignment from XAS data alone is challenging. Metal–ligand covalency in these frameworks further complicates oxidation state assignment, as in the case of molecular dithiolene complexes.…”

“…11,12 The formation of crystalline 2-Mo at a much lower temperature supports the importance of the metal-toligand electron transfer in promoting framework formation. Notably, 1-Nb is the rst monometallic niobium metal-organic framework, [35][36][37] and 2-Mo is the rst monometallic molybdenum framework that is not constructed from paddlewheel building units. 11,38 If metal-to-ligand electron transfers occur exclusively through inner-sphere processes, the use of a trivalent precursor complex should yield charge-neutral frameworks of the general formula M 2 (Cl 2 dhbq) 3 , regardless of the nal redox states of the metals and ligands.…”

Deliberate Construction of Polyoxoniobates Exploiting the Carbonate Ligand

“…Interest in niobate‐based materials including inorganic frameworks [23] and hybrid frameworks (i.e. MOFs) [24] is growing, due to their unique basic (alkaline) character and expected stability, attributed to bond strength between a highly charged metal center and an organic linker. The biggest challenge with hybrid PONb‐heterometal materials has been and continues to be devising and executing synthetic strategies that enables assembly of phase‐pure materials without hydrolysis byproducts.…”