Andreas Kourtellaris

A microporous Cu2+ MOF based on a pyridyl isophthalic acid Schiff base ligand with high CO2 uptake

A new Cu2+ complex that was isolated from the initial use of 5-((pyridin-4-ylmethylene)amino)isophthalic acid (PEIPH2) in 3d metal–organic framework (MOF) chemistry is reported. Complex {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞ denoted as Cu-PEIP·7DMF was isolated from the reaction of Cu(NO3)2·2.5H2O with PEIPH2 in N,N-dimethylformamide (DMF) at 100 °C and contains both the PEIP2− ligand and its 5-NH2-mBDC2− fragment. After the structure and properties of Cu-PEIP were known an analogous complex was prepared by a rational synthetic method that involved the reaction of Cu(NO3)2·2.5H2O, 5-((pyridin-4-ylmethyl)amino)isophthalic acid (PIPH2 – the reduced analogue of PEIPH2) and 5-NH2-mBDCH2 in DMF at 100 °C. Cu-PEIP comprises two paddle-wheel [Cu2(COO)4] units and exhibits a 3D-framework with a unique trinodal underlying network and point symbol (4.52)4(42·54·64·83·92)2(52·84). This network consists of pillared kgm-a layers containing a hexagonal shaped cavity with a relatively large diameter of ∼8–9 A surrounded by six trigonal shaped ones with a smaller diameter of ∼4–5 A and thus resembles the structure of HKUST-1. Gas sorption studies revealed that Cu-PEIP exhibits a 1785 m2 g−1 BET area as well as high CO2 sorption capacity (4.75 mmol g−1 at 273 K) and CO2/CH4 selectivity (8.5 at zero coverage and 273 K).

Preparation of Blatter Radicals via Aza-Wittig Chemistry: The Reaction of N-Aryliminophosphoranes with 1-(Het)aroyl-2-aryldiazenes

Reacting N-aryliminophosphoranes with 1-(het)aroyl-2-aryldiazenes in preheated diphenyl ether at ca. 150-250 °C for 5-25 min affords in most cases the 1,3-diaryl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yls (aka Blatter radicals) in moderate to good yields. All new compounds are fully characterized, including EPR and CV studies for the radicals. Single-crystal X-ray structures of 1-benzoyl-2-(perfluorophenyl)diazene and 1-(perfluorophenyl)-3-phenyl-1,4-dihydrobenzo[e][1,2,4]triazinyl are also presented.

Selective CO2 adsorption in water-stable alkaline-earth based metal–organic frameworks

Four novel metal–organic frameworks (MOFs) built from alkaline-earth metal ions and the flexible tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid (H4L) were synthesized using solvothermal methods. A variety of three-dimensional frameworks were obtained when employing different alkaline earth ions with the formula [Mg2(L)(H2O)(DMA)]·DMA (1), [Ca4(L)2(DMA)3] (2), [Ca4(L)2(H2O)2(DMA)2]·(3DMA) (3) and [Sr4(L)2(DMF)4]·(2DMF) (4) reflecting the variation in the ionic radius of alkaline-earth ions as well as the key role of the synthetic conditions used. By removing the guest molecules, a framework shrinking was observed driven by the structural flexibility of the H4L ligand. This resulted in large diffusional resistances towards N2 over CO2 molecules, therefore leading to a good CO2/N2 separation selectivity. Both Ca-based MOFs were very stable up to 98% relative humidity, while Mg- and Sr-based MOFs were much less stable.

5,6,7,8-Tetrafluoro-1-(2-nitrophenyl)-3-phenyl-1H-benzo[e][1,3,4]oxadiazine

Treating 1-fluoro-2-nitrobenzene (6) with N′-pentafluorophenylbenzohydrazide (7) and K2CO3 (1.1 equiv) in EtOH at ca. 110 °C (sealed tube) for 24 h affords 5,6,7,8-tetrafluoro-1-(2-nitrophenyl)-3-phenyl-1H-benzo[e][1,3,4]oxadiazine (5) (36%) and N′-(2-nitrophenyl)-N′-(perfluorophenyl)benzohydrazide (3) (37%). The X-ray crystallography of 5,6,7,8-tetrafluoro-1-(2-nitrophenyl)-3-phenyl-1H-benzo[e][1,3,4]oxadiazine (5) is provided. Microwave irradiation (100 W) of perfluorophenylbenzohydrazide 3 with K2CO3 (1.1 equiv) in THF at ca. 120 °C (sealed tube, 80 PSI) for 3 h gives oxadiazine 5 (85%), while reduction of the nitro group using Sn (4 equiv) in glacial acetic acid at ca. 20 °C for 30 min, followed by cyclodehydration at ca. 118 °C for 20 min and treatment with 2 M NaOH for 24 h resulted in 1-(perfluorophenyl)-3-phenyl-1,2,4-benzotriazin-4-yl (4) with 93% yield.

Redox Active Quinoidal 1,2,4-Benzotriazines

Modifying the para-quinonimine 1,3-diphenyl-1,2,4-benzotriazin-7(1 H)-one (2a) ( E1/2-1/0 -1.20 V), by replacing the N1-phenyl by pentafluorophenyl, the C3-phenyl by trifluoromethyl, or the C7 carbonyl by ylidenemalononitrile, led to improved electron affinities as determined by cyclic voltammetry and computational studies. Combining structural changes further improved electron accepting abilities: the most electron deficient analogues ( E1/2-1/0 ∼ -0.65 V) involved combining the ylidenemalononitrile groups at C7 with the trifluoromethyl groups at C3. 1,2,5-Thiadiazolo fusion at C5-C6 did not affect the redox behavior but did enhance the UV-vis absorption profile. During the synthesis of the thiadiazolo analogues, 1,4-thiazino-fused analogues 6 were obtained in low yield, which thermally ring contract to the triazafluoranthenones 7. Compounds are fully characterized, and X-ray data are provided for selected analogues.

Reticular Chemistry and the Discovery of a New Family of Rare Earth (4, 8)-Connected Metal-Organic Frameworks with csq Topology Based on RE4(μ3-O)2(COO)8 Clusters

In recent years, the design and discovery of new metal-organic framework (MOF) platforms with distinct structural features and tunable chemical composition has remarkably enhanced by applying reticular chemistry rules and the molecular building block (MBB) approach. We targeted the synthesis of new rare earth (RE)-MOF platforms based on a rectangular-shaped 4-c linker, acting as a rigid organic MBB. Accordingly, we designed and synthesized the organic ligand 1,2,4,5-tetrakis(4-carboxyphenyl)-3,6-dimethyl-benzene (H4L), in which the two methyl groups attached to the central phenyl ring lock the four peripheral carboxyphenyl groups to an orthogonal/vertical position. We report here a new family of RE-MOFs featuring the novel inorganic building unit, RE4(μ3-O)2 (RE: Y3+, Tb3+, Dy3+, Ho3+, Er3+, and Yb3+), with planar D2h symmetry. The rigid 4-c linker, H4L, directs the in situ assembly of the unique 8-c RE4(μ3-O)2(COO)8 cluster, resulting in the formation of the first (4, 8)-c RE-MOFs with csq topology, RE-csq-MOF-1. The structures of the yttrium (Y-csq-MOF-1) and holmium (Ho-csq-MOF-1) analogues were determined by single-crystal X-ray diffraction analysis. Y-csq-MOF-1 was successfully activated and tested for Xe/Kr separation. The results show that Y-csq-MOF-1 has high isosteric heat of adsorption for Xe (33.8 kJ mol-1), with high Xe/Kr selectivity (IAST 12.1, Henry 12.9) and good Xe uptake (1.94 mmol g-1 at 298 K and 1 bar), placing this MOF among the top-performing adsorbents for Xe/Kr separation.