Construction rules and structure prediction of zeolite frameworks containing 482 nets and spi

精品论文Construction rules and structure prediction of zeolite frameworks containing 4.82 nets and spiro-5 building units GUO Min1, LI Yi25(1. Jilin University Library, ChangChun 130012;2. State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, ChangChun 130012)Abstract: 4.82 nets and spiro-5 units have been found in several zeolite framework types, includingJOZ, NAB, WEI, LOV, RSN, and VSV. The different arrangement of spiro-5 units between the 4.8210nets leads to different framework types. By varying the locations of the spiro-5 units between the 4.82 nets, a number of hypothetical zeolite structures with feasible framework energies have been predicted. Keywords: inorganic chemistry; zeolite; 4.82-net; spiro-5; structure prediction0Introduction15Zeolites find widespread applications in catalysis, adsorption, and separation due to their unique pore architectures.1-2 Their 3-dimentional framework structures are constructed from tetrahedral coordinated Al and Si atoms (T atoms) bridged via O atoms. Different ways of connections between T atoms lead to different zeolite framework types. Up to now, 206 zeolite framework types have been approved by the International Zeolite Association.3 However, the20number of known zeolite framework types is far from enough to satisfy various industrial demands. During the past decades, many more efforts have been made on the synthesis of new zeolite framework types.4 One successful approach is to introduce new substituent elements, suchas Ge, Be, Zn, and Ga, etc., into the zeolite frameworks.5 These elements might play an importantstructure-directing role in the formation of specific building unit-containing zeolites.625Some structures feature structure building units of 4.82 nets and the rarely occurred spiro-5, which are linked together to form 3-D open-frameworks, which are frequently found in Be-containing zeolite types, such as in JOZ (beryllosiliacate)7, LOV (beryllosiliacate)8, WEI (beryllophosphate)9, and NAB (beryllosiliacate)10 and Zn containing zeolites, such as RSN (zincosilicates)11, and VSV (zincosilicates)12. This might be due to the fact that the smaller30Be/ZnOSi angle compared to typical SiOSi angle, that favors the formation of 3-rings.13Upon investigation of the construction regulations of this type of structures, a number of hypothetical structures containing 4.82 nets and spiro-5 units have been predicted by varying the locations of spiro-5 units between 4.82 nets. Energy calculations are performed on both hypothetical and known structures. The framework energies are used to evaluate the feasibility of35the proposed hypothetical structures. This structure prediction will provide feasible structures with specific structure building units and will be helpful for a synthetically oriented chemist.1MethodsStructure models were built up using the Cerius2 software package on an SGI O2+workstation.14 The geometry optimizations and the potential energy calculations were performed40using Burchart 1.01 force field assuming SiO2 compositions.15-16 The framework density (FD)was calculated as the number of T atoms per 1000 3.Foundations: Specialized Research Fund for the Doctoral Program of Higher Education (20090061120023) Brief author introduction:GUO Min, (1982-), femail, Librarian, Main research: chemical informatics. Correspondance author: LI Yi , (1978-), male, associate professor, Main research: structural chemistry of inorganic materials. E-mail: yili- 6 -2Results2.1 Construction RulesThe structures of 4.82 net and spiro-5 unit were given in Fig. 1. In the known zeolites, the 4.8245nets and the spiro-5 linkages could be found in only Be or Zn containing zeolite frameworks, such as, JOZ (beryllosiliacate)7,LOV (beryllosiliacate)8,WEI (beryllophosphate)9, NAB (beryllosiliacate) 10, RSN (zincosilicates) 11, and VSV (zincosilicates)12. The structures of WEI, NAB, and JOZ are constructed from typical 4.82 nets (as seen in Fig. 1), named single 4.82 nets here (designated as s), connected together via spiro-5 linkages. Whilst, in zeolite LOV, VSV, and50RSN, there exist double 4.82 nets (designated as d) and spiro-5 linkages. As shown in Fig. 2, thereare two types of double 4.82 nets found in known structures, denoted as d1 and d2, respectively. In LOV, two adjacent single nets stack together by bridging oxygen atoms to form a double 4.82 net (d1) which contains 4-rings inside; in VSV, two single nets form a double 4.82 net (d2) containing5-rings; while in RSN, both d1 and d2 could be found. All of the known zeotype frameworks55featuring 4.82 nets and the spiro-5 linkages are illustrated in Fig. 3. Oxygen atoms are omitted for clarity, and the 3-rings in spiro-5 units are highlighted with trigonal planes.Fig.1 The 4.82 net and spiro-5 unit. T atoms are designated as yellow balls. Oxygen atoms are omitted for clarity.60Fig.2 Two types of double 4.82 nets: (a) d1 containing 4-rings; (b) d2 containing 5-rings.Upon investigation of the construction regulation, its found that different arrangements of65spiro-5 units between 4.82 nets lead to different structures. Schematic drawings of the three types of spiro-5 arrangements between 4.82 nets in known structures are shown in Fig. 4 as types IIII. For clarity, only one periodically repeated unit of the 4.82 net is given. Each vertex stands for a TO4 tetrahedron. Each pair of tetrahedra forms a spiro-5 unit with another tetrahedra pair above or below this 4.82 net. Tetrahedra forming a spiro-5 unit above this net are shown as filled circles,70while those forming a spiro-5 unit below this net are shown as empty circles. Each connection between a pair of filled circles is shown as a empty line which stands for a spiro-5 unit above the net, while an empty line connecting a pair of empty circles stands for a spiro-5 unit below the net.It could be easily seen that different arrangements of filled and empty lines, i.e., upward and downward spiro-5 units, lead to different structure types. NAB, LOV, RSN, and VSV belong to75type I; while WEI and JOZ belong to types II and III, respectively (Fig. 4).Fig.3 Topologies of LOV, VSV, RSN, WEI, NAB, and JOZ, showing the different stacking ways of 4.82 nets and different arrangements of spiro-5 units. s and d represent single 4.82 net and double 4.82 net, respectively. Sprio-580units are shown as trigonal plane.Fig.4 Schematic drawings of the arrangements of spiro-5 units around one periodically repeated unit of the 4.82 net. I: LOV, VSV, RSN, NAB; II: WEI, H5; III: JOZ, H6, H7; IV: H1; VI: H2; V: H3; VII: H4. Filled circles and lines85stand for spiro-5 units above the 4.82 net; empty circles and lines stand for the spiro-5 units below the 4.82 net.2.2 Structure PredictionSimilarly, a number of hypothetical structure models could be built up from 4.82 nets (single4.82 nets or double 4.82 nets) and the spiro-5 units according to their different arrangements.90Theoretically, there are numerous feasible arrangements that can be used to construct the structures. Here, only four hypothetical arrangements types of IVVII are taken as examples (Fig.4). First, hypothetical structures were built up according to the above construction regulations.95100105110115Then, geometry optimization and energy calculation for each structure model were performed to refine the bonding geometries. The symmetry for each hypothetical structure model was rechecked after refinement. The feasibility of each hypothetical structure model was evaluated by comparing the framework energy with those of the known structures.17-19 The energy calculations for both hypothetical and known structures were based on the assumption that the composition of eachframework was SiO2. Structure modeling and energy calculations were performed using Accelrys Cerius2 software. Our calculation results show that all reasonable structure models have low framework energies. The framework energies for known structures and parts of our hypotheticalstructures (Hn) are listed in Tab. 1. It could be seen that these hypothetical structures have low framework energies ranging from -427.29 to -436.03 kcal/mol/T, which are comparable to those of the known structures.Fig.5 Hypothetical topologies of H1H7, showing the different stacking ways of 4.82 nets and different arrangements of spiro-5 units. s and d represent single 4.82 net and double 4.82 net, respectively. Sprio-5 units are shown as trigonal plane.H1 to H4 were built up by single 4.82 net (s) according to hypothetical arrangements of types IVVII, respectively; H5 and H6 were built up by double 4.82 net (d) according to arrangements of types II and III, respectively; while H7 was built up by the alternation of single 4.82 nets (s) and double 4.82 nets (d) according to arrangements of type III (Fig. 4 and Fig. 5). After structure refinement, H1 has a unit cell of a = 10.176 , c = 11.900 , space group of P-42m (no. 111), with FD of 16.11 T/ 10003. Its framework consists of intersecting 10-ring channels running along the 100 and 010 directions (Fig. 5, H1a). Besides, there are10-ring channels, look like9-ring channels running along the 110 direction. H2 and H3 are constructed with the same4-ringspiro-5 chain as in JOZ, whereas the location of spiro-5 units between two 4.82 nets are different from each other. Thus, unlike JOZ, only 2D interconnecting channel systems are found in H2 and H3 (H2, 010 8 2.7 3.3 * 001 8 4.5 4.9 *, H3, 010 10 1.1 5.9 * 120125130001 8 3.9 4.6 *). The refined framework of H4 has a unit cell with a = 12.185 , b = 9.396, c = 9.636 , = 102.72 in the space group of C2 (no. 5). Fig. 5 shows its framework with10-ring channels along the 001 direction.H5 has refined cell parameters of a = 10.044 , b = 21.536 , c = 10.098, space group of Cmma (no. 67), FD = 16.48 T/10003. Its framework contains 10-ring channels and 8-ring channels along the 100 direction. H6 and H7 have the same arrangement of spiro-5 between 4.82 nets as that in JOZ. The difference among them lies in the type of 4.82 net. H6 consists of double4.82 nets (d); H7 consists of alternately arranged single 4.82 nets (s) and double 4.82 nets (d1);while JOZ, as shown above, consists of only single 4.82 nets.Code4.82 netSequenceFDEnergyJOZsIII16.06-435.04WEIsII16.18-435.06NABsI16.24-435.32LOVd1I17.07-436.41RSNd2I17.54-436.38VSVd1, d2I17.16-436.24H1sIV16.11-435.04H2sV16.26-434.86H3sVI19.48-427.29H4sVII18.58-433.22H5d1II16.48-436.03H6d1III19.97-431.03H7s, d1III18.15-433.07Tab.1 Different 4.82 Nets, Sequences, Framework Densities (T/10003), and Framework Energies (kcal/mol /T) of the Known and Some Selected Hypothetical Structures.1351403ConclusionThe different arrangements of spiro-5 units between 4.82 nets lead to different framework structures. By varying the arrangement of the spiro-5 units between 4.82 nets, a number of feasible hypothetical structure models have been successfully built. It is believed that these hypothetical zeolite frameworks will be accessed synthetically by selecting suitable non-traditionalcomposition elements, such as Be and Zn atoms.References1451501551601 Breck D W. Zeolite Molecular Sieves Structure Chemistry and UsesM, New York: John Wiley & Sons Inc,1974.2 Davis M E. Ordered porous materials for emerging applicationsJ. Nature, 2002, 41: 813-821.3 Baerlocher C, McCusker L B, Database of Zeolite Structures. 2012. http:/www.iza-structure.org/databases.4 Yu J H. Synthesis of zeolites; Cejka J, van Bekkum H, Corma A, Schueth F. Ed, Elsevier Science: Amsterdam2007, 168: 39.5 Corma A, Diaz-Cabaas M J, Martinez-Triguero J, Rey F, Rius J. A large-cavity zeolite with wide pore windows and potential as an oil refining catalystJ. Nature, 2002, 418: 514-517.6 Wilson S T. 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Design of Chiral Zeolite Frameworks with Specified Channels through Constrained Assembly of AtomsJ. Chem. Mater., 2005, 17: 4399-4405.含有 4.82 网层和螺-5 结构单元的分子筛骨架构筑规则 和结构设计郭敏1，李乙2（1. 吉林大学图书馆，长春 130012；2. 吉林大学无机合成与制备化学国家重点实验室，长春 130012） 摘要：在已知分子筛中，有一些骨架结构是由 4.82 网层和螺-5 为基本的结构单元构筑而成 的，包括 JOZ、NAB、WEI、LOV、RSN、VSV。这些分子筛骨架结构的区别主要在于 4.82 网层和螺-5 结构单元的排列方式的不同。在此基础上，通过变换这两个结构单元的位置和 连接方式，可以预测结构多样的假象分子筛骨架结构类型。同时，通过理论计算获得这些假 想结构的骨架能量，并与已知分子筛结构相互比较。关键词：无机化学；分子筛；4.82 网层；螺-5；结构预测中图分类号：O611.2