Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol–gel preparation of nano-sized titania: Crystal and molecular structure of [Ti{ONC 10 H 16 } 4 2CH 2 Cl 2 ] Archana Chaudhary a , Veena Dhayal a , Meena Nagar a , Rakesh Bohra a,⇑ , Shaikh M. Mobin b , Pradeep Mathur b,c a Department of Chemistry, University of Rajasthan, Jaipur 302 004, India b National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India c Indian Institute of Technology Indore, M-Block, Institute of Engineering and Technology, Devi Ahilya Vishwavidyalaya Campus, Khandwa Road, Indore 452 017, Madhya Pradesh, India article info Article history: Received 25 July 2010 Accepted 16 December 2010 Available online 31 December 2010 Keywords: Oximato complexes Dihapto g 2 -(N, O) manner Hypercoordination Dimeric Monomeric Nano-sized abstract Reactions of [Ti(OPr i ) 4 ] with various oximes, in anhydrous refluxing benzene yielded complexes of the type [Ti{OPr i } 4n {L} n ], where, n = 1–4 and LH = (CH 3 ) 2 C@NOH (1–4), C 9 H 16 C@NOH (5–8) and C 9 H 18 C@NOH (9–12). The compounds were characterized by elemental analyses, molecular weight mea- surements, FAB-mass, FT-IR and NMR ( 1 H, 13 C{ 1 H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC 10 H 16 } 4 2CH 2 Cl 2 ](8A) suggests that the oximato ligands bind the metal in a dihapto g 2 -(N, O) manner, leading to the formation of an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decomposition with the formation of TiO 2 as the final product in each case, at 900 °C. Low temperature (600 °C) sol–gel transformations of ( 2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Composi- tions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two rep- resentative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recently, considerable attention has been paid on the synthesis of nano-structured titania due to its wide range applications, such as in highly specific chemical sensors [1], photocatalysis [2], optical coatings [3] and solar cells [4]. Sol–gel method using metal alkoxides or related precursors ap- pears to be one of the established routes for the preparation of pure titania [3b,5,6]. Search for more stable alkoxide precursors, have led to the development of chemical modification of parent alkox- ides, which can be achieved by replacing some or all of the alkoxy groups with chelating ligands, such as oximes, b-diketones, carbox- ylic acid and Schiff’s bases [5a,7]. It appears that the modification of the parent alkoxide with che- lating ligands not only controls the hydrolysis and condensation reactions but also give rise to new molecular precursors exhibiting interesting structural variations [8]. Understanding of the struc- tural and chemical aspects of the modified precursors is essential to tailor the materials with desired properties using sol–gel pro- cess [9]. Oximes, including functionalized oximes are excellent chemical modifiers [10–12]. They display the tendency of changing the coor- dination mode from side-on [10] to end-on [11] to bridging [12] as per the steric demand and chemical composition of the central me- tal leading the system towards maximum stability. Oxime func- tionalities also act as structure directing agents offering a precise control over the size of the synthesized materials. The growth of nanoparticle upon calcination is strongly inhibited when oximato ligands are present [12b]. Our recent results on the crystal struc- ture analyses of some oximato complexes of Zr(IV) [10a] and V(V) [10b,10c] indicate preferential binding of the oximato group to the transition metal via N and O in a dihapto g 2 -(N, O) manner. It is worthwhile to mention here that Mehrotra et al. [13] re- ported the syntheses and characterization of some oximato com- plexes of Ti(IV) and assumed monomeric, tetrahedral structure 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.12.025 ⇑ Corresponding author. Tel./fax: +91 0141 2700364. E-mail address: rkbohra@sifymail.com (R. Bohra). Polyhedron 30 (2011) 821–831 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly