Novel Ti−O−Ti Bonding Species Constructed in a Metal−Oxide Cluster:  Reaction Products of Bis(oxalato)oxotitanate(IV) with the Dimeric, 1,2-Dititanium(IV)-Substituted Keggin Polyoxotungstate

Abstract

The preparation and structural characterization of a novel Ti-O-Ti bonding complex constructed in a dilacunary alpha-Keggin polyoxometalate (POM), [[{Ti(ox)(H2O)}4(mu-O)3](alpha-PW10O37)](7-) (H2ox = oxalic acid) (1a), are described. The water-soluble, crystalline complex with a formula of K6H[1a].0.5KCl.10H2O (1p) was prepared as the bulk sample in 28.0% (0.51 g scale) yield in a 1:4 molar-ratio reaction of the dititanium(IV)-substituted, dimeric form of an alpha-Keggin POM, K10[(alpha-1,2-PW10Ti2O39)2].18H2O, with the titanium(IV) source K2[TiO(ox)2].2H2O in HCl-acidic solution (pH 0.08). Prior to formation of 1p, the KCl-free crystalline compound (1c) obtained was characterized with X-ray crystallography. The compound 1p was unequivocally characterized with complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, and solution (31P, 183W, and 13C) NMR spectroscopy. The molecular structure of 1a was determined. The POM 1a in the solid state was composed of the four octahedral Ti groups (four guests), i.e., the two Ti-O-Ti groups linked with the mu-O atom, incorporated to the two adjacent, octahedral vacant sites (two hosts) in the dilacunary Keggin POM. The formation of 1a, as well as the recently found POM [{Ti(ox)(H2O)}2(mu-O)](alpha-PW11O39)](5-) (2a), was strongly dependent on the reaction with [TiO(ox)2](2-), i.e., the anionic titanium(IV) complex as the titanium(IV) source. The POM 1a is contrasted to most titanium(IV)-substituted POMs consisting of a combination of a monolacunary site (one host) and an octahedral Ti group (one guest) and also contrasted to 2a as a combination of a monolacunary site (one host) and two octahedral Ti groups or a Ti-O-Ti group (two guests).

Chemistry of Group IV Metal Ion‐Containing Polyoxometalates

“…The formation of this complex can be represented in Equation (2). It should be noted that the dissociation process of the two host‐four guest type POM was not observed 24 …”

Transformation of Tri-Titanium(IV)-Substituted α-Keggin Polyoxometalate (POM) into Tetra-Titanium(IV)-Substituted POMs : Reaction Products of Titanium(IV) Sulfate with the Dimeric Keggin POM Precursor under Acidic Conditions

“…Although, in 1 , the Ti 4 center contained in the Keggin POM half unit may be also considered as a kind of three host-four guest coordination, it is only a combination of two Ti IV atoms based on one host-one guest coordination and two Ti IV atoms based on one host-two guest coordination. The previously reported, two host-four guest coordination can be also reconsidered as a combination of one host-two guest coordination [22]. The two sulfate ions bridged between the terminal positions of two Ti octahedra (central Ti4 octahedron and peripheral Ti1 or Ti2 octahedron).…”

“…From the viewpoint of host-guest chemistry of Ti-substitution in POM, in contrast to most Ti IV -substituted Keggin POMs consisting of a combination of a mono-lacunary site (one host) and an octahedral Ti group (one guest), an unusual host-guest relationship has been found in some recent POMs, [[{Ti(ox)(H 2 O)} 4 (μ-O) 3 ](α-PW 10 O 37 )] 7- (H 2 ox = oxalic acid) 3 [22] and [{Ti(ox)(H 2 O)} 2 (μ-O)](α-PW 11 O 39 )] 5- 4 [23]. The two host-four guest POM 3 [22] in the solid state is composed of four octahedral Ti groups (four guests), i.e.…”

“…The two host-four guest POM 3 [22] in the solid state is composed of four octahedral Ti groups (four guests), i.e. , the two intramolecular Ti-O-Ti bonds linked with the μ-O atom, incorporated to the two adjacent, octahedral vacant sites (two hosts) within the di-lacunary Keggin POM.…”

Novel Phosphotungstate-titania Nanocomposites from Aqueous Media

“…Notably, composites between polyoxometalate (POM) and titania have been studies widely in this regard. [5][6][7][8][9][10] The general synthetic method of this class of materials is the sol-gel reactions starting from metal alkoxides in alcoholic solvents.11-14 On the contrary, there have been quite few examples of producing porous metal oxides from aque ous systems probably because most of the metal ions of the oxides of interests are highly reactive in water so that their aqueous chemistry is practically uncontrollable.…”