Russell K. Feller

Structural diversity and chemical trends in hybrid inorganic–organic framework materials

Hybrid framework compounds, including both metal-organic coordination polymers and systems that contain extended inorganic connectivity (extended inorganic hybrids), have recently developed into an important new class of solid-state materials. We examine the diversity of this complex class of materials, propose a simple but systematic classification, and explore the chemical and geometrical factors that influence their formation. We also discuss the growing evidence that many hybrid frameworks tend to form under thermodynamic rather than kinetic control when the synthesis is carried out under hydrothermal conditions. Finally, we explore the potential applications of hybrid frameworks in areas such as gas separations and storage, heterogeneous catalysis, and photoluminescence.

Hybrid organic-inorganic framework structures: influence of cation size on metal-oxygen-metal connectivity in the alkaline earth thiazolothiazoledicarboxylates.

We report the synthesis of four organic-inorganic frameworks of alkaline earth cations with the organic ligand 2,5-thiazolo[5,4-d]thiazoledicarboxylate (C6N2S2O4(2-), Thz(2-)). Structures with remarkably different connectivities result when Mg(2+), Ca(2+), Sr(2+), and Ba(2+) react with Thz(2-). Mg(Thz)(H2O)4 (I) forms a 1-D coordination polymer in which one carboxylate oxygen on each terminus of the ligand connects individual MgO6 octahedra from their axial positions, while the remaining equatorial sites are coordinated by water molecules. Ca2(Thz)2(H2O)8 (II) forms a 1-D coordination polymer in which dimeric clusters with 7-fold Ca coordination are connected via the ligand in a linear fashion, with a second, uncoordinated Thz(2-) providing charge balance. Sr(Thz)(H2O)3 (III) has 1-D infinite inorganic connectivity built from edge-sharing SrO7N polyhedra having one carboxylate oxygen and one water molecule acting as M-O-M bridges. Ba2(Thz)2(H2O)7 (IV) has 2-D inorganic connectivity based upon face- and edge-sharing BaO9N polyhedra. One carboxylate oxygen and all water molecules act as bridges between each Ba(2+) and its three neighbors. We shall discuss the manner in which the increasing coordination requirements of the cations (MgO6 < CaO7 < SrO7N < BaO9N) lead to an increase in inorganic connectivity through the series.

Comparison of Chiral and Racemic Forms of Zinc Cyclohexane trans‐1,2‐Dicarboxylate Frameworks: A Structural, Computational, and Calorimetric Study

An integrated study of the organic-inorganic framework material zinc cyclohexane trans-1,2-dicarboxylate involving synthesis, structure elucidation, computer simulation, and calorimetry shows that the chiral R,R form (right in picture) is less stable than its racemic R,R/S,S analogue (left) and adopts a layered structure with a fundamentally different topology. The results point to the possibility that the structural diversity of racemic frameworks and their homochiral analogues may be much greater than has hitherto been suspected.

Synthesis and Structure of (Ph4P)2MCl6 (M = Ti, Zr, Hf, Th, U, Np, Pu)

High-purity syntheses are reported for a series of first, second, and third row transition metal and actinide hexahalide compounds with equivalent, noncoordinating countercations: (Ph(4)P)(2)TiF(6) (1) and (Ph(4)P)(2)MCl(6) (M = Ti, Zr, Hf, Th, U, Np, Pu; 2-8). While a reaction between MCl(4) (M = Zr, Hf, U) and 2 equiv of Ph(4)PCl provided 3, 4, and 6, syntheses for 1, 2, 5, 7, and 8 required multistep procedures. For example, a cation exchange reaction with Ph(4)PCl and (NH(4))(2)TiF(6) produced 1, which was used in a subsequent anion exchange reaction with Me(3)SiCl to synthesize 2. For 5, 7, and 8, synthetic routes starting with aqueous actinide precursors were developed that circumvented any need for anhydrous Th, Np, or Pu starting materials. The solid-state geometries, bond distances and angles for isolated ThCl(6)(2-), NpCl(6)(2-), and PuCl(6)(2-) anions with noncoordinating counter cations were determined for the first time in the X-ray crystal structures of 5, 7, and 8. Solution phase and solid-state diffuse reflectance spectra were also used to characterize 7 and 8. Transition metal MCl(6)(2-) anions showed the anticipated increase in M-Cl bond distances when changing from M = Ti to Zr, and then a decrease from Zr to Hf. The M-Cl bond distances also decreased from M = Th to U, Np, and Pu. Ionic radii can be used to predict average M-Cl bond distances with reasonable accuracy, which supports a principally ionic model of bonding for each of the (Ph(4)P)(2)MCl(6) complexes.

A hybrid cobalt disulfonate with a novel inorganic layer architecture exhibiting a field-induced magnetic transition

We report the synthesis, crystal structure, and magnetic properties of Co3(OH)4(ethanedisulfonate), a layered cobalt hydroxide pillared by ethanedisulfonate ligands (P21/c, a = 8.9462(6) A, b = 5.2818(4) A, c = 10.1259(7) A, β = 93.297(2)°, V = 477.68(6) A3, Z = 2). The structure displays two-dimensional infinite Co–O–Co connectivity, with the octahedra forming what we believe is a novel M3X8 inorganic layer topology; brucite-like ribbons of edge-sharing octahedra share corners with other ribbons along a second direction to form perforated layers of octahedra. Magnetic measurements reveal a sharp peak in susceptibility at 38 K, with a Curie–Weiss constant of −243 K and an effective magnetic moment (µeff) of 4.35 µB per Co. A field-induced transition from a triangular antiferromagnetic to a collinear ferrimagnetic state occurs in high fields. Heat capacity measurements indicate a relatively small magnetic entropy change, suggesting that the magnetic ordering is only two-dimensional. Thermogravimetric analysis and differential thermal analysis of the material show stability to 350 °C.