Yun-Xia Che

Five novel cobalt coordination polymers: effect of metal–ligand ratio and structure characteristics of flexible bis(imidazole) ligands

Five novel metal–organic frameworks (MOFs) have been hydrothermally synthesized, namely, [Co(bimb)(2,4′-bpdc)(H2O)2]·H2O (1), [Co2(bimb)3(2,4′-bpdc)2(H2O)2]·H2O (2), [Co(bix)(2,4′-bpdc)] (3), [Co(bix)0.5(2,4′-bpdc)(H2O)0.25] (4) and [Co(bimh)(2,4′-bpdc)] (5), based on mixed ligands, 2,4′-biphenyldicarboxylic acid (2,4′-H2bpdc) as organic linkers and different bis(imidazole) ligands as co-ligands: (1,4-bis(imidazol-1-yl)-butane (bimb), 1,4-bis(imidazol-1-yl-methylene)-benzene (bix) and 1,6-bis(imidazol-1-yl)-hexane (bimh)). The coordination polymers were characterized by single-crystal X-ray diffraction, thermogravimetric analysis (TGA) and element analysis (EA). Reactions between CoCl2·6H2O, 2,4′-H2bpdc and neutral bimb ligand afforded two crystallographically different coordination polymers (1 and 2) through tuning the ligand/metal ratio meticulously. Compound 1 crystallizes in a noncentrosymmetric Pna21 space group with 65·8 CdSO4-type topology, while compound 2 is isolated with P21/c space group and displays a 4-connected 66 network. By substituting bix for bimb ligand, alteration of the metal/ligand ratio in the initial reaction system induced a transition from 2D layer (compound 3) to 3D architecture (compound 4). Notably, the structure of 4 is constructed from [Co(2,4′-bpdc)] layers, which are further pillared by bix ligands into a 3D 3,4-connected (63)·(63·103) network. In 5, the left- and right-handed helical chains constructed by Co(II) and bimh ligands are bridged by 2,4′-bpdc2− anions to form a layer-like structure.

An unusual metal–organic framework showing both rotaxane- and cantenane-like motifs

Via hydro(solvo)thermal synthesis, the self-assembly of Cd(NO3)2, L1 and L2 generated compound 1, Cd2(L1)(L2)2 (L1 = 1,1′-(1,4-butanediyl)bis(imidazole), L2 = pamoic acid) which presents an uncommon interpenetrating metal–organic framework in that it contains both rotaxane- and catenane-like motifs.

Network topology and property studies for two binodal self-penetrated coordination polymers

Two coordination polymers, [CoIICuI(m-BDC)(BIPY)1.5(m-NBZ)]n (1) and [CoII4(BPTC)2(BBI)4]n (2), (where BIPY = 4,4′-bipyridine, BBI = 1,1′-(1,4-butanediyl)bis(imidazole), m-BDC = 1,3-benzenedicarboxylate, m-HNBZ = m-nitrobenzoic acid and H4BPTC = 3,3′,4,4′-biphenyltetracarboxylic acid), have been obtained under solvo/hydrothermal conditions, which were characterized by single-crystal X-ray diffraction, XRPD, IR, ICP, TGA, and elemental analysis. Both 1 and 2 feature two unusual binodal self-penetrated architectures: 1 presents a 2-D network with (4·62)2(42·62·82) topology in terms of the rationalization of T-shaped CuI and Co2 unit as 3- and 4-connected node, respectively; however, compound 2 built up from a flexible long-chain ligand and a polycarboxylate confers a 3-D (62·84)(64·82)2 net based on the definition of square-planar and tetrahedral 4-connected nodes. The magnetic study of 1 was carried out in the temperature range of 5–300 K, showing antiferromagnetic coupling interaction within the dimeric Co2 unit. In addition, 1 was found to exhibit fluorescence at about 420 nm (λex = 330 nm).

Metal–ligand ratio-controlled assembly of two pairs of Co(II) complexes: syntheses, structures and magnetic properties

Reactions of Co(II) salts with rigid 5-amino-isophthalic acid (AIP) and flexible bis(imidazole) ligands by controlling the metal–ligand ratio gave rise to two pairs of new complexes: [Co(AIP)(bimb)] (1) and [Co(AIP)(bimb)0.5] (2), [Co(AIP)(bix)]·H2O (3) and [Co2(AIP)2(bix)1.5] (4) (bimb = 1,4-bis (imidazol-1-yl)-butane, bix = 1,4-bis(imidazol-1-yl-methylene)-benzene). Comparative study revealed that the different metal–ligand ratios affected the coordination modes of the ligand and thus resulted in four different structures. All complexes display 2D structures and extend into 3D supramolecular frameworks via intermolecular hydrogen bonds. Complex 1 features a (4,5)-connected hydrogen-bond network. Complex 2 displays a 2D bilayered structure with a rare (3,4)-connected (63)(65 ·8) topology. Complex 3 is an 2D (4,4) network showing 2-fold parallel interpenetrating 2D → 2D structure, which features the 2-fold interpenetrating cds hydrogen-bond net. Complex 4 shows a trinodal (4,4,5)-connected hydrogen-bond net. Magnetic studies of 1 reveal ferromagnetic interaction at low temperature and 4 displays antiferromagnetic behavior.

A variety of novel complexes constructed from biphenyl-3,3′,4,4′-tetracarboxylate and flexible bis(imidazole) ligands

A polycarboxylate ligand, biphenyl-3,3′,4,4′-tetracarboxylic acid (H4bptc), as an organic linker with different flexible bis(imidazole) ligands as co-ligands were selected to react with metal ions under hydrothermal conditions and six new metal–organic frameworks consisting of 1D, 2D and 3D structures were successfully isolated. Compound 1 is a fascinating self-penetrating network with the [Co2L12] loops and 2D [Co(bptc)0.5] sheet intra-catenated (L1 = 1,4-bis(imidazol-1-yl-methylene)-benzene). Compounds 2 and 3 feature an identical binodal 4-connected (64·82)2(65·8) net. Compound 4 is a 1D chain containing loops that further interconnected via O–H⋯O hydrogen bonds to form a 3D supramolecular framework. Compounds 5 and 6 are both corrugated 2D networks, however, the 1D [Zn(bptc)0.5] chains are linked by [Zn2L42] metallocycles in 5 and a pair of 1D [Cd(L4)]n chains in 6 (L4 = 1,1′-(2,2′-oxybis(ethane-2,1-diyl))bis(1-imidazole)). A comparison of all complexes demonstrates that the coordination modes of bptc4− anions and the structural characteristics of flexible N-donor ligands simultaneously play an important role in the construction of the complexes.

Two new metal–triazole-benzenedicarboxylate frameworks affording an uncommon 3,4-connected net and unique 4,6-connected rod packing: hydrothermal synthesis, structure, thermostability and luminescence studies

Two new metal–triazole-benzenedicarboxylate coordination polymers are obtained by the hydrothermal self-assembly of Zn(or Cd)(NO3)2, trz, and 1,3-H2BDC(or 1,4-H2BDC), where trz and BDC are triazole and benzenedicarboxylate. Polymer 1, Zn(trz)(1,3-HBDC), crystallizes in the P21/c space group and shows the 2D fes 4·82 net, which is further extended via strong O–H⋯O/2.641 A hydrogen bonds, creating the supramolecular 3,4-connected net described by (4·82)(4·82·103) Schlafli symbol. Polymer 2, Cd4(H2O)2 (trz)2(1,4-BDC)3·H2O, have the C2/c space group and complicated 3D architecture, an architecture that is comprised of two distinct rod-like substructures, viz. 4-connected {Cd(trz)(H2O)(CO2)}n of corner-sharing octahedra and 6-connected {Cd(trz)(CO2)}n of edge-sharing octahedra. In the solid, both 1 and 2 have strong luminescence, viz. 453 nm for 1 and 398 nm for 2, which suggests the potential luminescence material of 1 and 2.

Unprecedented trinodal 4-connected metal–organic frameworks (MOFs) with 2-fold interpenetration

Via hydrothermal synthesis, the self-assembly of Co(SCN)2 with the mixed rigid and flexible N,N′-bidentate donors, 4,4′-bpy and bimb (4,4′-bpy = 4,4′-bipyridine, bimb = 1,4-bis(imidazol-1-yl)-butane), generated a novel complex: [Co(bimb)(4,4′-bpy)(SCN)2] (1), which is the first example of an extended coordination polymer incorporating these mixed neutral N,N′-bidentate ligands. The structure contains (4,4) 2D [Co4(4,4′-bpy)2(bimb)4] layers further pillared by 4,4′-bpy ligands to form an unusual 3D framework that can be classified as a 4-connected (64·82)(63·83)2(65·8) net based on three kinds of planar Co nodes. Two of these nets interpenetrate.

Two Acentric Mononuclear Molecular Complexes with Unusual Magnetic and Ferroelectric Properties

Two acentric, i.e., noncentrosymmetric, mononuclear complexes, Co(5-ATZ)(4)Cl(2), 1, and Cu(5-ATZ)(4)Cl(2), 2, where 5-ATZ is the monodentate 5-amino-1-H-tetrazole ligand, have been prepared and characterized. Both complexes crystallize in the tetragonal system with the P4nc space group, a member of the polar noncentrosymmetric 4mm class, and thus both 1 and 2 can exhibit ferroelectric and nonlinear optical properties. Magnetic studies indicate that 1 is a paramagnetic high-spin cobalt(II) complex with a rather extensive spin-orbit coupling, modeled as a zero-field splitting parameter, D, of ±91(3) cm(-1) and with very weak long-range antiferromagnetic exchange interactions. Direct current (dc) and ac magnetic studies indicate that 2 is a paramagnetic copper(II) complex that exhibits weak ferromagnetic exchange interactions below 15 K. Both 1 and 2 exhibit ferroelectric hysteresis loops at room temperature with remanent polarizations of 0.015 μC/cm(2) and coercive electric fields of 5.5 and 5.7 kV/cm, respectively.

Rod-packing motif: a new metal–organic polymer showing unusual rod-packing architecture

A new metal–organic polymer, namely {Co(2,2′,4,4′-H2bptc)}n (1), 2,2′,4,4′-H4bptc = biphenyl-2,2′,4,4′-tetracarboxylic acid) obtained viahydrothermal reaction, compound 1 shows an unusual hex-type rod-packing architecture. Moreover, the magnetic studies of 1 disclose a weak intra-chain ferromagnetic interaction.

Three 3d–4f heterometallic complexes constructed from oxalic acid and benzimidazole-5,6-dicarboxylic acid

Three 3d–4f heterometallic complexes, namely, [Co3Ln2(L)4(C2O4)2(H2O)2·6H2O]n (Ln = Pr (1), Nd (2), Sm (3); H2L = benzimidazole-5,6-dicarboxylic acid, H2C2O4 = oxalic acid), have been synthesized hydrothermally and characterized by single crystal X-ray diffraction study, IR, TGA and elemental analysis. The three complexes are isostructural; in their structures, the Co(II) centers are connected into a linear Co3 cluster by the C2O42− anions, the Ln(III) centers are connected into one-dimensional (1D) {Ln–O–C}n rod-like chains by the carboxyl groups of L2− anions, the linear Co3 clusters and {Ln–O–C}n rod-like chains are further connected by the L2− anions, and finally construct three 3D frameworks, which contain 1D channels along the b direction occupied by (H2O)8 clusters. In addition, magnetic studies of the three complexes all reveal antiferromagnetic behaviors.