Nona-coordinated MO 6 N 3 centers M = Zr, Hf as a stable building block for the construction of heterometallic alkoxide precursors Gerald I. Spijksma a,b , Lars Kloo c , Henny J.M. Bouwmeester a , Dave H.A. Blank a , Vadim G. Kessler b, * a Inorganic Materials Science, Faculty of Science and Technology and MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands b Department of Chemistry, SLU, Box 7015, 75007 Uppsala, Sweden c Inorganic Chemistry, Royal University of Technology, 100 44 Stockholm, Sweden Received 20 March 2006; received in revised form 12 October 2006; accepted 20 October 2006 Available online 27 October 2006 In memory of Professor Liliane G. Hubert-Pfalzgraf – a protagonist in the solution and gas phase stability studies of heteroleptic heterometallic alkoxide precursors of oxide materials. Abstract The modification of zirconium or hafnium alkoxides with diethanolamine, H 2 dea, leads to the formation of unique nona-coordinated M{l-g 3 -NH(C 2 H 4 O) 2 } 3 cores. The mechanism is used to develop a self-assembly approach to the first thermodynamically stable zirco- nium–titanium and hafnium–titanium precursors, Zr{l-g 3 -NH(C 2 H 4 O) 2 } 3 [Ti(O i Pr) 3 ] 2 (1) and Hf{l-g 3 -NH(C 2 H 4 O) 2 } 3 [Ti(O i Pr) 3 ] 2 (2). Mass spectrometric characterization of these compounds demonstrates their volatility. In addition to the solution stability of these com- pounds the volatility makes them attractive single source precursors for MOCVD and ALD applications. These precursors are also inter- esting candidates for application in sol–gel synthesis of microporous materials as the stability of the core prevents self-assembly of ligands on the outer surface of the primary particles formed during the hydrolysis. A n-propoxide analog of 1 can be prepared from zir- conium n-propoxide but does not yield any crystalline material. It is demonstrated that 1 can be prepared from [Zr(O n Pr)(O i Pr) 3 ( i PrOH)] 2 , however, with a lower yield compared to the use of zirconium isopropoxide. The single crystals obtained from systems con- taining zirconium isopropoxide, titanium isopropoxide and triethanolamine H 3 tea turned out to be Ti 2 (O i Pr) 2 ({l-g 4 -NH(C 2 H 4 O) 3 } 2 ) 2 (4). Theoretical calculations indicate that the octacoordinate M{l-g 4 -N(C 2 H 4 O) 3 } 2 core, anticipated in reaction with H 3 tea, will have metal–nitrogen bonds that are too long for its stabilization. This explains why the formation of 4 is thermodynamically favored over the formation of heterometallic species. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Precursor design; Hetrometallic alkoxides; Solution stability; Gas phase stability; X-ray single crystal study 1. Introduction Sol–gel materials based on zirconium, hafnium and tita- nium oxides are used in a broad spectrum of applications, ranging from mesoporous materials for catalyst supports and membranes [1,2] to high-tech applications as thin films, fibers [3,4], aerogels [5] and (nano-) particles [6–8]. Thin films can be applied as a micro-membrane layer [9–11], high-temperature thermal barrier coatings or ferroelectrics [12]. Interest in materials containing both titanium and its heavy analogs (zirconium and hafnium) in their composi- tion has grown, such as PZT, PLZT and especially recently – the lead-free BZT [13–15]. The mineral srilankite, ZrTi 2 O 6 , has shown very attractive dielectric properties [16]. A strong difference in reactivity and volatility between 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.10.022 * Corresponding author. E-mail address: Vadim.Kessler@kemi.slu.se (V.G. Kessler). www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 2045–2055