Structural parameters for the incomplete cuboidal cluster cation: [Nb3(μ3-Cl)(μ-O)3(OH2)9]4+ in solutions of acid hydrolysed trivalent niobium from Nb K edge EXAFS

Preparation, Properties, and Reactivities of Unprecedented Oxo-Sulfido Nb(IV) Aqua Ions and Crystal Structure of (Me2NH2)6[Nb5(μ3-S)2(μ3-O)2(μ2-O)2(NCS)14]·3.5H2O

“…This is a general feature for metal ions with low d-electron populations, which is the case for Nb(IV), and has been observed with d 1 and d 2 hexa-aqua metal ions such as [Ti(H 2 O) 6 ] 3+ , [Mo(H 2 O) 6 ] 3+ , and [V(H 2 O) 6 ] 3+ . Interestingly, water-exchange reaction on the Nb(III,IV 2 ) aqua ion, [Nb 3 (Cl)O 3 (H 2 O) 9 ] 4+ , shows no conjugate-base labilizating effect either, and an associative mechanism has been deduced from activation parameters. , The π-electron donation from the S 2 2- to the Nb(IV) in Nb 2 (S 2 ) 2 4+ , which increases the electron density at the Nb atoms, may be responsible for the anomalous behavior.…”

“…Sometimes, a small amount of the yellow [Nb 2 (μ 2 -S 2 ) 2 (H 2 O) 8 ] 4+ aqua ion (hereafter, Nb 2 (S 2 ) 2 4+ ) closely preceded these two species. The Nb 3 ClO 3 4+ and Nb 2 (S 2 ) 2 4+ species were identified by comparison of the observed and published UV−visible spectra. , Upon the column being washed with 3 M HCl, the highly charged yellow-brown aqua ion [Nb 5 (μ 3 -S) 2 (μ 3 -O) 2 (μ 2 -O) 2 (H 2 O) 14 ] 8+ eluted. A dark brown band remained on the column and eluted very slowly with 4−5 M HCl.…”

“…The aqueous solution chemistry of niobium, on the other hand, remains largely unexplored. Since the report on the first aqua ion of niobium, purportedly the green [Nb 3 O 4 (H 2 O) 9 ] 3+ ion (later evidence favors the formulation of [Nb 3 (Cl)O 3 (H 2 O) 9 ] 4+ ), which was crystallized as thiocyanate derivative (NH 4 ) 3 (Me 4 N) 3 [Nb 3 SO 3 (NCS) 9 ]·MeOH in 1986, , the dimeric [Nb 2 (μ 2 -S 2 ) 2 (H 2 O) 8 ] 4+ aqua ion is the only other aqua complex of niobium reported . Very different synthetic approaches were employed, with the trimeric complex being synthesized by treatment of [Nb 2 Cl 6 (tht) 3 ] (tht = tetrahydrothiophene) with concentrated hydrochloric acid, whereas the dimeric complex was obtained from the polymeric NbS 2 Cl 2 lead-in compound by reaction with potassium thiocyanate followed by treatment of the melt with water.…”

Ligand Substitution Reactions at Inorganic Centers

“…Reactions on the corresponding homotungsten clusters show similar reactivity trends to the molybdenum species above but with slower rates (factor of 10) . With characterization of [Nb 3 (μ 3 -S)(μ-O) 3 (NCS) 9 ] 6- 266 and [Nb 3 (μ 3 -Cl)(μ-O) 3 (H 2 O) 9 ] 4+ , − examples of such trimetal clusters extend into group 5. [Nb 3 (μ 3 -Cl)(μ-O) 3 (H 2 O) 9 ] 4+ is moreover interesting in that no conjugate base labilizing effect is apparent for exchange at the d-H 2 O's 267 although they remain much more labile (factor of 10 4 ) than the c-H 2 O's.…”

An Unprecedented Tetranuclear Niobium Aqua Ion with a Capping μ4-Sulfido Ligand

“…Upon reaction of the green aqua ion with thiocyanate, crystals of (NH 4 ) 3 (Me 4 N) 3 [Nb 3 SO 3 (NCS) 9 ]·MeOH were obtained, and the structure determined by X-ray crystallography revealed the presence of a μ 3 -S. The μ 3 -S is believed to originate from the thiocyanate. However, EXAFS studies suggested the formula [Nb 3 (μ 3 -Cl)O 3 (H 2 O) 9 ] 4+ rather than [Nb 3 O 4 (H 2 O) 9 ] 3+ for the aqua ion . Although there is still a lack of direct structural proof for this niobium aqua ion, it has provided indications that niobium can form species similar to molybdenum in acidic aqueous solutions, where the triangular [Mo 3 O 4 - x Q x (H 2 O) 9 ] 4+ (Q = S, Se) aqua ions are very well characterized .…”