Paul Jensen

The ligand, the metal and the ‘Holey’-host: Synthesis, structural and magnetic characterisation of Co(II), Ni(II) and Mn(II) metal–organic frameworks incorporating 4,4′-dicarboxy-2,2′-bipyridine

We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4-dicarboxy-2,2-bipyridine ligand, H(2)dcbp: alpha-[Co(dcbp)(H(2)O)(2)], 1; beta-[Co(dcbp)(H(2)O)(2)], 2, [Ni(dcbp)(H(2)O)(2)], and [[Mn(dcbp)].1/2DEF], 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1:1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6(4)8(2)-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water-carboxylate double helices in , and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm(-3)(1.654 vs. 1.940 g cm(-3), respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1-3 and has a (4.6(2))(4(2).6)(4(3).6(6).8(6)) Schlafli notation. Magnetic susceptibility studies performed on 1, 2, [[Mn(dcbp)].1/2DMF] 5 (DMF = dimethylformamide) and [[Mn(dcbp)].2H(2)O] 6 reveal very weak antiferromagnetic coupling between the metal centres in each case.

The role of acid in the formation of hydrogen-bonded networks featuring 4,4'-dicarboxy-2,2'-bipyridine (H2dcbp): Synthesis, structural and magnetic characterisation of {[Cu(H2dcbp)Cl2].H2O}2 and [Cu(H2dcbp)(NO3)2(H2O)]

Reported herein are the synthesis, structural and magnetic characterisation of two hydrogen-bonded networks featuring the 4,4′-dicarboxy-2,2′-bipyridine (H2dcbp) ligand: {[Cu(H2dcbp)(Cl)2]·H2O}2xa01xa0and [Cu(H2dcbp)(NO3)2(H2O)]xa02. Compoundsxa01xa0andxa02xa0result from the reaction of CuCl2 and Cu(NO3)2, respectively, with H2dcbp under hydrothermal conditions in the presence of either HCl or HNO3. The acid ensures that H2dcbp remains protonated and provides the anions required for charge balance irrespective of Cu(II) precursor. Withinxa01xa0andxa02xa0the H2dcbp ligand performs a dual role of Cu(II) coordination,xa0viaxa0the 2,2′-bipyridine moiety, and propagates the formation of chains through hydrogen-bonding involving the peripheral 4,4′-dicarboxylic acid functionalities. Additional hydrogen bonding between the 4,4′-dicarboxylic acid groups, metal bound chloride and nitrate anions, inxa01xa0andxa02xa0respectively, and water molecules generate 3D networks. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between the Cu(II) centres across the chloride bridges inxa01xa0(Jxa0= n −3.02 cm−1).

Coordination and hydrogen bonded networks featuring 4,4?-dicarboxy-2,2?-bipyridine (H2dcbp): structural characterisation of H2dcbp, [Co(dcbp)(H2O)4]·4H2O, and {[Cu(dcbp)(H2O)2]·2H2O}n

We report herein the single crystal structures of 4,4′-dicarboxy-2,2′-bipyridine, H2dcbp, and two complexes it forms with Co(II), [Co(dcbp)(H2O)4]·4H2O, 1, and Cu(II), {[Cu(dcbp)(H2O)2]·2H2O}n, 2. H2dcbp adopts the anti conformation in the solid-state, with a dihedral angle of 148° between each pyridyl ring. Face-to-face π⋯π interactions reinforce intermolecular hydrogen bonding (O–H⋯N) involving both carboxylate oxygen and pyridyl nitrogen atoms forming a 2D inter-helical network. Alternate 2D layers are of opposite chirality and are linked into 3D through (C–H⋯O) hydrogen bonds. In both 1 and 2 the ligand is deprotonated giving neutral complexes with 1 ∶ 1 stoichiometry. Although 1 is monomeric, extensive hydrogen bonding between the deprotonated carboxylates, lattice water, and coordinated water molecules results in a 3D network which also contains face-to-face π⋯π interactions between adjacent dcbp ligands. Within 2, pseudo-octahedral coordination about the Cu(II) centre is furnished by bidentate bipyridyl nitrogens, two monodentate carboxylates (from two adjacent dcbp ligands) and two water molecules. Coordination of dcbp in this instance forms a 2D coordination polymer, which is further linked by extensive hydrogen bonding between carboxylates and water molecules, giving a 3D network.

Synthesis and structural characterisation of two coordination polymers (molecular ladders) incorporating [M(OAc)2]2 secondary building units and 4,4′-bipyridine [M = Cu(II), Zn(II)]

We report herein the synthesis and structural characterisation of two coordination polymers: {[Cu(4,4′-bipy)(OAc)2]·2.5H2O}n1 and {[Zn(4,4′-bipy)(OAc)2]}n2, which feature dissimilar dimeric metal acetate secondary building units linked through 4,4′-bipyridine to yield 1D molecular ladders. In 1, the ladders connect via n(C–H⋯O) hydrogen bonds to generate 2D sheets, which further link via n(C–H⋯π) hydrogen bonds to give a 3D supramolecular network. A 3D network in 2 results directly from a combination of (C–H⋯O) and (C–H⋯π) hydrogen bonding. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between Cu(II) centres across the acetato bridges in 1 n(J n= n−1.18 cm−1).

Hybrid materials containing organometallic cations and 3-D anionic metal dicyanamide networks of type [Cp*2M][M'(dca)3].

A new series of hybrid materials of type [Cp*2M][M(dca)3] has been prepared by cation templation and structurally characterised (M = Fe(III), Co(III); M= Mn(II), Fe(II), Co(II), Ni(II), Cd(II); dca-= N(CN)2-). The crystallographic analysis of [Cp*2Fe][Cd(dca)(3)] showed that the [Cd(dca)3]- anionic framework is of a symmetrical 3-D alpha-polonium type, containing octahedral Cd nodes and micro (1,5)-dca bridging ligands. The [Cp*2Fe]+ cations occupy the cube-like cavities within the framework. The cationic and anionic-framework sublattices remain magnetically independent and display susceptibilities, over the range 300 to 2 K, of a Curie-Weiss nature obtained by adding a S= 1/2 (Cp*2Fe+) or a S= 0 (Cp*2Co+) contribution to those of the weakly antiferromagnetically coupled frameworks of M. These hybrid species do not show any intrinsic long-range magnetic order. The present [Cp*2Fe]M(dca)3] series display the characteristic, unusually shaped [Cp*2Fe]+ Mossbauer line, in the range 295-5 K, assigned (below 101 K) as the sum of a narrow and a broad line. Relaxation effects were evident. The [Fe(dca)3]- compound showed superimposed low-spin Fe(III) and high-spin Fe(II) lines, the latter giving relaxation broadening effects.

The ‘Trinity’ helix: synthesis and structural characterisation of a C3-symmetric tris-bidentate ligand and its coordination to Ag(I)

The synthesis and structural characterisation of a novel C3-symmetric tris-bidentate ligand, L, featuring a triphenylamine core appended by pyridylimine coordination sites is reported: 1H NMR compleximetric titration studies with Ag(I) and ESMS indicate the presence of [Ag3L2]3+ species in solution, consistent with the formation of a trinuclear double helicate complex: the Trinity helix.