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-) (H(2)ox=oxalic acid) (1a), are described. The water-soluble, crystalline complex with a formula of K6H[1a]center dot 0.5KCl center dot 10H(2)O (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, K-10[(alpha-1,2- PW10Ti2O39)(2)]center dot 18H(2)O, with the titanium(IV) source K-2[TiO(ox)(2)]center dot 2H(2)O 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 (P-31,W-183, and C-13) 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).