Quantum chemical calculations on the stability of dierent conformations of silicate building block structures in relevance to zeolite synthesis Sailaja Krishnamurty a , Sourav Pal a , Annick Goursot b , Rajappan Vetrivel a, * a National Chemical Laboratory, Pune 411 008, India b Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 CNRS-ENSCM, 8 rue de l' Ecole Normale, F-34296 Montpellier Cedex 5, France Received 6 August 2000; received in revised form 3 December 2000; accepted 23 December 2000 Abstract The relative in¯uence of various geometric parameters such as bond lengths, bond angles and dihedral angles on the energetics of silicate structures is studied. The in¯uence of dihedral angles, in particular, on the preferred conformation and energy of silicate building blocks is highlighted. The possibility of formation of ring structures and the diameters of the rings will depend on these Si±O±Si±O and O±Si±O±Si dihedral angles. Dierent conformations were obtained for a dimer cluster model by varying the two types of dihedral angles and their relative stability was studied using quantum chemical calculations. The study of variation of the dihedral angles on the stability of silicate structures is further extended to larger cluster models. The importance of dihedral angles is discussed in the context of formation of silicate building blocks during the synthesis of zeolites. The combinations of Si±O±Si±O and O±Si±O±Si dihedral angles, such as 0° and 60°, 120° and 300° etc., leading to staggered adjacent SiO 4 groups are energetically preferred. The energetic preference of the staggered structures over eclipsed structures is an order of magnitude higher for pentamers cluster models than for dimers cluster models. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Zeolite synthesis; Quantum chemical calculations; Building blocks; Si±O±Si±O angle; O±Si±O±Si angle 1. Introduction The knowledge on various processes that are involved during the nucleation of solids from the gel is important not only in the context of synthesis of dierent zeolites, but also for ceramics and many other novel materials [1]. Recent studies on the formation of zeolite structures have high- lighted the role of small molecular entities as sig- ni®cant species participating in the synthesis of various zeolite structures [2,3]. In this context, there have been several experimental [4±6] and computational [7±12] attempts to understand the exact role of these small molecular species and their condensation leading to larger units dur- ing the formation of regular 3-d framework. It has been proposed that the nucleation process is followed by growth process [13,14]. The growth Microporous and Mesoporous Materials 48 2001) 383±390 www.elsevier.com/locate/micromeso * Corresponding author. Present address: GE India Tech- nology Centre, White®eld Road, Bangalore 560 066, India. E-mail address: rajappan.vetrivel@geind.ge.com R. Vetri- vel). 1387-1811/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S1387-181101)00361-4