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...

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A new family of 14-electron, four-coordinate iron(II) complexes of the general formula [Tp(tBu,Me)FeX] (Tp(tBu,Me) is the sterically hindered hydrotris(3-tert-butyl-5-methyl-pyrazolyl) borate ligand and X=Cl (1), Br, I) were synthesized by salt metathesis of FeX(2) with Tp(tBu,Me)K. The related fluoride complex was prepared by reaction of 1 with AgBF(4). Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four-coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single-crystal X-ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high-spin (d(6), S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.

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The reaction of [Ru(CO)2Cl2] n with 2,6-bis(di-tert-butylphosphinomethyl)pyridine) (PNP) and then anion exchange yields [Ru(PNP)(CO)2Cl]PF6 (1). Reaction of 1 with AgBF4, in acetone, followed by acetonitrile and then anion exchange gave [Ru(PNP)(CO)2(CH3CN)](PF6)2 (2); reaction of 2 with water gave [Ru(PNP)(CO)2OH]PF6 (3), whereas reaction of 2 with aqueous KOH led to [Ru(PNP)(CO)(CH3CN)H]PF6 (4). Complexes 3 and 4 have been structurally characterized.