In the field of porous supramolecular metal complexes, both molecular [1] and extended-solid [2] materials have been extensively studied in recent years. These materials are attractive due to their applications in gas storage [3] and host-guest chemistry.[4] Among the most often studied of these species are the metal-containing "molecular squares", that is, squareshaped porous tetrameric structures. These have been prepared by several approaches, the most common being the reaction of an organic bridging ligand with a metal complex that has available cis coordination sites (Figure 1 a). The bridging ligand is frequently a pyridine derivative (for example, 4,4'-bipyridine (4,4'-bpy)), [5] although bis-chelating ligands have also been used. [6] In these cases, the 908 "corners" in the molecular squares are provided by metal complexes. The resulting metal centers are usually coordinatively saturated, which makes it difficult for guest molecules to interact directly with the metal atoms. Herein we report molecular squares prepared by an alternative approach, in which bifunctional organic moieties serve as the "corners" and join metal atoms in the centers of the "sides" (Figure 1 b). [7] These molecular squares are formed in one step, by reaction of bis(b-diketone) ligands (1) (Scheme 1). The new squares (2) are capable of binding guests in both a s (for example, 4,4'-bpy) and p fashion (for example, C 60 ), and they are also surprisingly effective for hydrogen-gas storage, both at 77 K and at room temperature.Ligands 1 a and 1 b were synthesized by reaction of isophthalaldehyde with 2,2,2-trimethoxy-4,5-dimethyl-1,3,2-dioxaphospholene and 2,2,2-trimethoxy-4,5-diethyl-1,3,2-dioxaphospholene, respectively, at room temperature and heating the intermediate in methanol under nitrogen. [8] Mixing solutions of 1 a or 1 b in CH 2 Cl 2 with aqueous [Cu(NH 3 ) 4 ] 2+ produces 2 a or 2 b, respectively, which can be isolated as dark green solids in approximately 95 % yield.The angles between the two b-diketone moieties in the new ligands 1 are about 1208. Thus, we anticipated that their reaction with metal ions would yield hexamers, for example, [M 6 (m-pba) 6 ]. However, X-ray analysis of the crystalline products 2, which are formed in nearly quantitative yield, shows that they are actually molecular squares, with diameters of about 14 (Figure 2).[9] (We explored a variety of conditions for preparing 2, but found no evidence of other oligomers.) Thus, 2 a and 2 b are unusual examples of molecular squares in which the corners are organic bridging groups, and the metal atoms are in the centers of the sides.The angles between the b-diketone moieties in the structures of 2 a and 2 b are still approximately 1208. To accommodate this angle within an overall square shape, there must be some distortion elsewhere in the molecule. The two ligands are coplanar with the metal atoms in an undistorted [Cu(b-diketonate) 2 ] complexes, [10] while, in the present squares, the ligands are all bent away from coplanarity.The formation of...

In the field of porous supramolecular metal complexes, both molecular [1] and extended-solid [2] materials have been extensively studied in recent years. These materials are attractive due to their applications in gas storage [3] and host-guest chemistry.[4] Among the most often studied of these species are the metal-containing "molecular squares", that is, squareshaped porous tetrameric structures. These have been prepared by several approaches, the most common being the reaction of an organic bridging ligand with a metal complex that has available cis coordination sites (Figure 1 a). The bridging ligand is frequently a pyridine derivative (for example, 4,4'-bipyridine (4,4'-bpy)), [5] although bis-chelating ligands have also been used. [6] In these cases, the 908 "corners" in the molecular squares are provided by metal complexes. The resulting metal centers are usually coordinatively saturated, which makes it difficult for guest molecules to interact directly with the metal atoms. Herein we report molecular squares prepared by an alternative approach, in which bifunctional organic moieties serve as the "corners" and join metal atoms in the centers of the "sides" (Figure 1 b). [7] These molecular squares are formed in one step, by reaction of bis(b-diketone) ligands (1) (Scheme 1). The new squares (2) are capable of binding guests in both a s (for example, 4,4'-bpy) and p fashion (for example, C 60 ), and they are also surprisingly effective for hydrogen-gas storage, both at 77 K and at room temperature.Ligands 1 a and 1 b were synthesized by reaction of isophthalaldehyde with 2,2,2-trimethoxy-4,5-dimethyl-1,3,2-dioxaphospholene and 2,2,2-trimethoxy-4,5-diethyl-1,3,2-dioxaphospholene, respectively, at room temperature and heating the intermediate in methanol under nitrogen. [8] Mixing solutions of 1 a or 1 b in CH 2 Cl 2 with aqueous [Cu(NH 3 ) 4 ] 2+ produces 2 a or 2 b, respectively, which can be isolated as dark green solids in approximately 95 % yield.The angles between the two b-diketone moieties in the new ligands 1 are about 1208. Thus, we anticipated that their reaction with metal ions would yield hexamers, for example, [M 6 (m-pba) 6 ]. However, X-ray analysis of the crystalline products 2, which are formed in nearly quantitative yield, shows that they are actually molecular squares, with diameters of about 14 (Figure 2).[9] (We explored a variety of conditions for preparing 2, but found no evidence of other oligomers.) Thus, 2 a and 2 b are unusual examples of molecular squares in which the corners are organic bridging groups, and the metal atoms are in the centers of the sides.The angles between the b-diketone moieties in the structures of 2 a and 2 b are still approximately 1208. To accommodate this angle within an overall square shape, there must be some distortion elsewhere in the molecule. The two ligands are coplanar with the metal atoms in an undistorted [Cu(b-diketonate) 2 ] complexes, [10] while, in the present squares, the ligands are all bent away from coplanarity.The formation of...

The title compound, C24H26O2Si2, has C 2 crystallographic symmetry. The dihedral angle between the aromatic rings is 84.5 (2)°. The acetyl­ene group is slightly non-linear, with angles at the acetyl­ene C atoms of 175.7 (2) and 177.0 (2)°. In the crystal structure, only van de Waals interactions occur.

The title mol­ecule, C11H13NO3, has its propanoic acid group in an extended conformation, such that the mol­ecule is nearly planar, with a mean deviation of 0.036 Å [the maxima being 0.106 (1) and 0.110 (1) Å for the two methyl­ene C atoms]. The NH group forms an intra­molecular hydrogen bond with the acetyl group; in the crystal COOH group forms a centrosymmetric hydrogen-bonded dimer.

Key indicators: single-crystal X-ray study; T = 90 K; mean (C-C) = 0.003 Å; R factor = 0.050; wR factor = 0.119; data-to-parameter ratio = 13.5.In the title structure, C 7 H 9 N 3 O 2 ÁH 2 O, there are two formula units in the asymmetric unit. The molecule is a zwitterion, containing a quaternary N atom and a deprotonated carboxyl group, with C-O distances in the range 1.256 (2)-1.266 (3) Å . The two independent molecules form a hydrogen-bonded R 2 2 (16) dimer about an approximate inversion center via N-HÁ Á ÁO hydrogen bonds, with NÁ Á ÁO distances of 2.766 (2) and 2.888 (2) Å . O-HÁ Á ÁO hydrogen bonds involving the water molecules and additional N-HÁ Á ÁO hydrogen bonds link these dimers, forming double chains. Related literature ExperimentalCrystal data