Published: September 15, 2011r2011

Published: September 15, 2011
r2011 American Chemical Society 675 dx.doi.org/10.1021/cr200205j |Chem. Rev. 2012, 112, 675–702
REVIEW
pubs.acs.org/CR
Deconstructing the Crystal Structures of Metal
Organic Frameworks and Related Materials into Their Underlying Nets Michael O’Keeffe*,†,‡ and Omar M. Yaghi*,‡,§ †Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States ‡Center for Reticular Chemistry, Center for Global Mentoring, Department of Chemistry and Biochemistry, University of California
Los Angeles, 607 Charles E. Young Dr. East, Los Angeles, California 90095, United States§ Graduate School of EEWS, Korea Advanced Institute of Science and Technology, Daejeon, Korea
CONTENTS
1. Introduction 675 2. Identi fi cation, Description, and Characterization of Nets 676 3. Edge Nets, Augmented Nets, and the Underlying Topology 677 4. The Deconstruction of Crystal Structures 678 4.1. Crystals with Corundum Net (cor) 678 4.2. Some Symmetrical Metal-Containing SBUs 679 4.3. Some Simple Organic SBUs 680 4.4. Some Structures with the pts Topology 683 4.5. Two MOFs Whose Preferred Description Is Not the pts Topology 684 4.6. MOFs with Multiple Links between SBUs 685 4.7. Examples of Lower-Symmetry Metal- Containing SBUs 686 5. Some Case Studies 687 5.1. A MOF with ubt Topology 687 5.2. MOFs with Hexatopic Carboxylate Linkers 687 5.3. MOFs with Octatopic Linkers 689 5.4. More on Metal Cluster SBUs 690 5.5. More Structures with Linked MOPs 691 5.6. A Cyclodextrin MOF 694 5.7. The Hierarchical Underlying Nets of MIL-101 and MIL-100 694 6. MOFs with Rod SBUs 696 6.1. SBUs as Zigzag Ladders 696 6.2. A MOF with a Twisted Ladder Rod SBU 697 6.3. A MOF with Rod SBUs of Linked Tetrahedra 697 6.4. Two-Way Rod SBUs of Linked Tetrahedra 697 6.5. MOFs with Rod SBUs of Linked Octahedra 698 6.6. Rod SBUs That Resist Simpli fi cation 698 7. MOFs with Ring SBUs 698 7.1. Coda 699 8. Concluding Remarks 699 Author Information 699 Biographies 699 Acknowledgment 700 References 700
1. INTRODUCTION The synthesis and characterization of metal
organic frame- works (MOFs) is one of the most rapidly developing areas of chemical science. These materials have unquestionably enor- mous potential for many practical applications, as detailed else- where in this issue, but they also often have exceptionally beautiful structures. It is the identification and description of the nets that describe the underlying topology of these structures that is the main topic of this review. In particular we emphasize that this is not a review of MOF structures per se. Why should we care about nets and related structural aspects of crystals? First and foremost, as chemists we recog- nize that the very core of our science lies in describing, and perhaps understanding, how atoms organize themselves, sometimes with our help, in chemical compounds. Such knowledge is also essential to designed (“rational”) synthesis of MOFs and related materials from component parts, as has beenstressedrecently.1 For this, of course, one needs to know the principal possibilities, which, as discussed below, have been established systematically only in the past few years. By deconstruction, we mean simply the reverse of the thought process that goes into designed synthesis, that is, breaking down a complex structure into its fundamental units with- out losing their chemical significance. One can think of it as reverse engineering. Another reason for knowing about nets and their occurrences is a result of the dramatic advances in methods of computer simulationofMOF
adsorbateinteractions,especiallycalculated adsorption isotherms, which makes the computer prescreening of potential materials an attractive procedure.2 Of course, to do this usefully it must be performed for materials for which there is a reasonable prospect of actual synthesis, which in turn will be done by design. From the very earliest days of crystallography, simple inor- ganic structures were shown as “ball-and-stick” models in which the balls were the atoms and the sticks corresponded to bonds presumed to exist between nearest-neighbor atoms.3 It was early realized, particularly by Wells,4 that such models could be considered as representations or embeddings of special kinds of abstract graphs called nets (defined below) with the vertices of thegraphcorrespondingtotheatomsandtheedges(links)ofthe
Special Issue: 2012 Metal-Organic Frameworks
Received: June 6, 2011
676 dx.doi.org/10.1021/cr200205j |Chem. Rev. 2012, 112, 675–702
Chemical Reviews REVIEW
graph corresponding to the bonds. Wells devoted much effort to enumerating nets, but he focused almost entirely on structures with three- and/or four-coordinated vertices and placed special emphasis on structures with shortest cycles (closed paths around the net) of all the same size; he called these structures uniform nets. Although he correctly recognized the importance of struc- tures with symmetry-related vertices and edges, in fact, he found only very few of those now known. It also became apparentthatthesametopology(net) was found in many different chemical contexts. It was also realized that the edges and vertices of the net could be respectively polyatomic linkers andclusters.Thework of theIwamotogroup oncyanides is notableinthisrespect.Complexcyanideswithnetsofformsofsilica (cristobalite, tridymite and keatite) of other binary compounds such as rutile (TiO2), pyrite (FeS2), and cooperite (PtS) were prepared and their nets identified.5 The term “mineralomimetic” was coined to describe this kind of chemistry. An important next step was the realization that, in fact, certain topologies could be targeted, especially for cyanides, by assem- bling appropriately shaped components.6,7 The wide variety of chemical compounds amenable to this approach was subse- quently emphasized in several reviews.7,8 It should be empha- sized,however, thatit was ingeneral rare for an underlyingnetto be identified in the older literature, and furthermore, when a net was identified, it was often done incorrectly. This last criticism applies far too often also to recent work. Indeed, the diligent reader will find that some of the examples adduced in this review were originally assigned either to no topology or to an incorrect one. However, it is less the purpose here to correct errors than to point the way to better analyses in the future. The discovery of MOFs, a term used here particularly to describe robust and highly porous metal
organic frameworks, led to the recognition that, in order to truly obtain structures by design, one had first to identify the principal topological possi- bilities for nets. These, which were termed default structures,9,10 were identified as those with high point symmetry at the vertices and with a small number of different kinds of vertex and edge— two conditions that are, of course, highly correlated. Subsequent analysis of published structures confirmed the predominance of these default topologies.11 The discipline of preparing materials of targeted geometry by design is termed reticular chemistry10 and a series of com- pounds with the same underlying topology (net) is called an isoreticular series.12 As already mentioned, for successful reti- cular chemistry one needs to know the principal topologies, and a concerted effort was made to enumerate them.13 The most important of the these are nets with one kind of edge (edge transitive) most of which were unknown prior to this work but are now realized to be of special importance. A review under the rubric “Taxonomy of Nets and the Design of Materials” has been published.14 Data for many of the nets most important for reticular chemistry are collected in a searchable database known as the Reticular Chemistry Structure Resource (RCSR).15 There nets are assigned three-letter symbols such as abc, or symbols with extensions as in abc-d (see below). This database is rather small (about 2000 entries). A much larger database is being developed in the EPINET project, which currently contains about 15000 three-periodic nets.16 The computer program TOPOS recog- nizes even more, about 70000.17 In this connection, mention should also be made to the extensive enumerations of sphere packingsbyFischerandassociates.18 The nets ofthesestructures
have just one kind of vertex and have an embedding in which all the shortest (and equal) intervertex distances correspond to edges of the net. Most of these are incorporated in the RCSR.
2. IDENTIFICATION, DESCRIPTION, AND CHARACTER- IZATION OF NETS A net is just a special sort of graph. It is simple, meaning that thereisatmostoneundirectededgethatlinksanypairofvertices, and there are no loops (edges linking a vertex to itself). A net is also connected, meaning that every vertex is linked to every other by a continuous path of edges. The net of a polyhedron is finite. In crystals we will have infinite nets that are one-, two-, or three- periodic (“dimensional”). The emphasis here will be on three- periodic nets. Graph-theoretical aspects, in particular terminol- ogy and definitions, have been given elsewhere.19 By “underlying topology” we mean the innate structure of the net associated with the crystal structure. Topology is really a branch of mathematics (or several branches as some would have it). However, here we use the term, following common usage, to refer to the combinatorial structure of a graph that is invariant in different embeddings.20 In this review we show how a net is extracted from a crystal structure. The first question is, what is the identity of the net? Thiscanbeansweredinameaningfulwayonlybysayingthatitis identical to a previously known net that has an identifier (such as a RCSR symbol). Otherwise, the net is new. The only algorithm devised to do this in a mathematically rigorous way is realized in Olaf Delgado
Friedichs’ program Systre.21 It should be men- tioned, though, that in practice the program TOPOS17

Kết quả (Việt) 1:

Được đăng: Ngày 15 tháng 9 năm 2011r2011 Mỹ hóa học xã hội 675 dx.doi.org/10.1021/cr200205j |Chem. Rev 2012, 112, 675-702ĐÁNH GIÁpubs.acs.org/CRDeconstructing cấu trúc tinh thể của kim loại hữu cơ khung và các vật liệu có liên quan vào tiềm ẩn của lưới Michael O'Keeffe *, †, ‡ và Omar M. Yaghi *, ‡, § †Department hóa học và hóa sinh, đại học bang Arizona, Tempe, Arizona 85287, Hoa Kỳ ‡Center Reticular hóa học, Trung tâm tư vấn toàn cầu, vùng hóa học và hóa sinh, đại học California tại Los Angeles, 607 Charles E. Young tiến sĩ East, Los Angeles, California-90095 , Vương States§ tốt nghiệp trường EEWS, Hàn Quốc nâng cao Viện khoa học và công nghệ, Daejeon, Hàn QuốcNỘI DUNG1. giới thiệu 675 2. Identi fi cation, mô tả, và đặc tính của lưới 676 3. Cạnh lưới, lưới tăng cường, và tô pô tiềm ẩn 677 4. Deconstruction Crystal cấu trúc 678 4.1. Tinh thể với Corundum Net (màu) 678 4.2. Một số đối xứng có chứa kim loại SBUs 679 4.3. Một số, đơn giản SBUs hữu cơ 680 4.4. Một số cấu trúc với điểm tô pô 683 4.5. Hai MOFs Whose ưa thích mô tả là không điểm tô pô 684 4.6. MOFs với nhiều liên kết giữa SBUs 685 4.7. Ví dụ về đối xứng thấp hơn kim loại - có SBUs 686 5. Một số trường học 687 5.1. Một MOF với ubt tô pô 687 5.2. MOFs với Hexatopic Carboxylate Linkers 687 5.3. MOFs với Octatopic Linkers 689 5.4. Biết thêm về kim loại cụm SBUs 690 5.5. Thêm cấu trúc với liên kết MOPs 691 5,6. Một Cyclodextrin MOF 694 5.7. Lưới phân cấp cơ bản của MIL-101 và MIL-100 694 6. MOFs với Rod SBUs 696 6.1. SBUs như Zigzag Thang đoạn 696 6.2. Một MOF với một cây gậy bậc thang xoắn SBU 697 6.3. Một MOF với Rod SBUs của tứ diện liên kết 697 6.4. Hai chiều Rod SBUs của tứ diện liên kết 697 6.5. MOFs với Rod SBUs của liên kết Octahedra 698 6.6. Rod SBUs rằng chống lại Simpli fi cation 698 7. MOFs với vòng SBUs 698 7.1. Coda 699 8. Kết luận nhận xét 699 tác giả thông tin 699 tiểu sử 699 thừa nhận 700 tham chiếu 7001. INTRODUCTION The synthesis and characterization of metal
organic frame- works (MOFs) is one of the most rapidly developing areas of chemical science. These materials have unquestionably enor- mous potential for many practical applications, as detailed else- where in this issue, but they also often have exceptionally beautiful structures. It is the identification and description of the nets that describe the underlying topology of these structures that is the main topic of this review. In particular we emphasize that this is not a review of MOF structures per se. Why should we care about nets and related structural aspects of crystals? First and foremost, as chemists we recog- nize that the very core of our science lies in describing, and perhaps understanding, how atoms organize themselves, sometimes with our help, in chemical compounds. Such knowledge is also essential to designed (“rational”) synthesis of MOFs and related materials from component parts, as has beenstressedrecently.1 For this, of course, one needs to know the principal possibilities, which, as discussed below, have been established systematically only in the past few years. By deconstruction, we mean simply the reverse of the thought process that goes into designed synthesis, that is, breaking down a complex structure into its fundamental units with- out losing their chemical significance. One can think of it as reverse engineering. Another reason for knowing about nets and their occurrences is a result of the dramatic advances in methods of computer simulationofMOF
adsorbateinteractions,especiallycalculated adsorption isotherms, which makes the computer prescreening of potential materials an attractive procedure.2 Of course, to do this usefully it must be performed for materials for which there is a reasonable prospect of actual synthesis, which in turn will be done by design. From the very earliest days of crystallography, simple inor- ganic structures were shown as “ball-and-stick” models in which the balls were the atoms and the sticks corresponded to bonds presumed to exist between nearest-neighbor atoms.3 It was early realized, particularly by Wells,4 that such models could be considered as representations or embeddings of special kinds of abstract graphs called nets (defined below) with the vertices of thegraphcorrespondingtotheatomsandtheedges(links)oftheSpecial Issue: 2012 Metal-Organic FrameworksReceived: June 6, 2011676 dx.doi.org/10.1021/cr200205j |Chem. Rev. 2012, 112, 675–702Chemical Reviews REVIEWgraph corresponding to the bonds. Wells devoted much effort to enumerating nets, but he focused almost entirely on structures with three- and/or four-coordinated vertices and placed special emphasis on structures with shortest cycles (closed paths around the net) of all the same size; he called these structures uniform nets. Although he correctly recognized the importance of struc- tures with symmetry-related vertices and edges, in fact, he found only very few of those now known. It also became apparentthatthesametopology(net) was found in many different chemical contexts. It was also realized that the edges and vertices of the net could be respectively polyatomic linkers andclusters.Thework of theIwamotogroup oncyanides is notableinthisrespect.Complexcyanideswithnetsofformsofsilica (cristobalite, tridymite and keatite) of other binary compounds such as rutile (TiO2), pyrite (FeS2), and cooperite (PtS) were prepared and their nets identified.5 The term “mineralomimetic” was coined to describe this kind of chemistry. An important next step was the realization that, in fact, certain topologies could be targeted, especially for cyanides, by assem- bling appropriately shaped components.6,7 The wide variety of chemical compounds amenable to this approach was subse- quently emphasized in several reviews.7,8 It should be empha- sized,however, thatit was ingeneral rare for an underlyingnetto be identified in the older literature, and furthermore, when a net was identified, it was often done incorrectly. This last criticism applies far too often also to recent work. Indeed, the diligent reader will find that some of the examples adduced in this review were originally assigned either to no topology or to an incorrect one. However, it is less the purpose here to correct errors than to point the way to better analyses in the future. The discovery of MOFs, a term used here particularly to describe robust and highly porous metal
organic frameworks, led to the recognition that, in order to truly obtain structures by design, one had first to identify the principal topological possi- bilities for nets. These, which were termed default structures,9,10 were identified as those with high point symmetry at the vertices and with a small number of different kinds of vertex and edge— two conditions that are, of course, highly correlated. Subsequent analysis of published structures confirmed the predominance of these default topologies.11 The discipline of preparing materials of targeted geometry by design is termed reticular chemistry10 and a series of com- pounds with the same underlying topology (net) is called an isoreticular series.12 As already mentioned, for successful reti- cular chemistry one needs to know the principal topologies, and a concerted effort was made to enumerate them.13 The most important of the these are nets with one kind of edge (edge transitive) most of which were unknown prior to this work but are now realized to be of special importance. A review under the rubric “Taxonomy of Nets and the Design of Materials” has been published.14 Data for many of the nets most important for reticular chemistry are collected in a searchable database known as the Reticular Chemistry Structure Resource (RCSR).15 There nets are assigned three-letter symbols such as abc, or symbols with extensions as in abc-d (see below). This database is rather small (about 2000 entries). A much larger database is being developed in the EPINET project, which currently contains about 15000 three-periodic nets.16 The computer program TOPOS recog- nizes even more, about 70000.17 In this connection, mention should also be made to the extensive enumerations of sphere packingsbyFischerandassociates.18 The nets ofthesestructureshave just one kind of vertex and have an embedding in which all the shortest (and equal) intervertex distances correspond to edges of the net. Most of these are incorporated in the RCSR.2. IDENTIFICATION, DESCRIPTION, AND CHARACTER- IZATION OF NETS A net is just a special sort of graph. It is simple, meaning that thereisatmostoneundirectededgethatlinksanypairofvertices, and there are no loops (edges linking a vertex to itself). A net is also connected, meaning that every vertex is linked to every other by a continuous path of edges. The net of a polyhedron is finite. In crystals we will have infinite nets that are one-, two-, or three- periodic (“dimensional”). The emphasis here will be on three- periodic nets. Graph-theoretical aspects, in particular terminol- ogy and definitions, have been given elsewhere.19 By “underlying topology” we mean the innate structure of the net associated with the crystal structure. Topology is really a branch of mathematics (or several branches as some would have it). However, here we use the term, following common usage, to refer to the combinatorial structure of a graph that is invariant in different embeddings.20 In this review we show how a net is extracted from a crystal structure. The first question is, what is the identity of the net? Thiscanbeansweredinameaningfulwayonlybysayingthatitis identical to a previously known net that has an identifier (such as a RCSR symbol). Otherwise, the net is new. The only algorithm devised to do this in a mathematically rigorous way is realized in Olaf Delgado
Friedichs’ program Systre.21 It should be men- tioned, though, that in practice the program TOPOS17