Seik-Weng Ng

Polynuclear Complexes with Alkoxo and Phenoxo Bridges from In Situ Generated Hydroxy‐Rich Schiff Base Ligands: Syntheses, Structures, and Magnetic Properties

Complexes of new Schiff base ligands generated in situ from the reaction of 1-aminoglycerol, aldehydes, and metal ions are reported. [Cu4(HL(1))4] (1) and [Ni4O(HL(1))3(H2O)3)]⋅6u2009H2O⋅DMF⋅DMSO (2) have M4O4 cubane cores, with the L/M molar ratios of 4:4 and 3:4, respectively. [Mn(III)3Mn(II)NaOCl4(HL(1))3]⋅3u2009MeCN (3) has a unique pentanuclear trigonal propeller-shaped Mn(III)3Mn(II)Na core structure, and the coordination assemblies are linked by hydrogen bonds to afford a 3D channel structure. [Cu2(HL(2))2] (4) has a bis(μ2-alkoxo)-bridged Cu2O2 core, with the binuclear species linked by hydrogen bonds to afford a 1D double-chain. [Ni7(OH)2(OCH3)4(H2L(3)2(MeOH)2(H2O)2]-(ClO4)2⋅10u2009H2O (5) has a heptanuclear structure containing heptadentate di-Schiff base ligands, with the nickel(II) ions bridged by phenoxo, alkoxo, hydroxo, and methoxo groups to afford a very rare face-sharing hexadruple defective cubane core with a Ni@Ni6 arrangement. The lattice water molecules are linked by hydrogen bonds to form helical chains, which are further hydrogen-bonded to the coordination moieties to afford a 2D network. Variable temperature magnetic susceptibility measurements and nonlinear data-fitting revealed that the 2+4 type of cubane complex 1 shows medium intradimeric ferromagnetic interactions and weak interdimeric ferromagnetic interactions. For complexes 2 and 5, coexistent ferro- and antiferromagnetic couplings afford a non-zero spin ground state. However, compound 3 shows antiferromagnetic interactions between Mn(III) and Mn(II) , and ferromagnetic interactions between the Mn(III) centers, resulting in a global antiferromagnetic behavior. In conclusion, the reaction of 1-aminoglycerol with aldehydes and metal salts afforded polynuclear complexes with a rich structural diversity and remarkable magnetic behavior.

Neo-Fused Hexaphyrin : A Molecular Puzzle Containing an N-Linked Pentaphyrin

The first neo-confused hexaphyrin(1.1.1.1.1.0) was synthesized by oxidative ring closure of a hexapyrrane bearing two terminal confused pyrroles. The new compound displays a folded conformation with a short interpyrrolic C⋅⋅⋅N distance of 3.102u2005Å, and thus it readily underwent ring fusion to afford a neo-fused hexaphyrin with an unprecedented 5,5,5,7-tetracyclic ring structure. Furthermore, coordination of Cu(II) triggered a ring opening/contracting reaction to afford a Cu(II) complex of an N-linked pentaphyrin derivative. The roles of reactive N-C bonds in the porphyrinoid macrocycles were demonstrated.

A series of Zn-4f heterometallic coordination polymers and a zinc complex containing a flexible mixed donor dicarboxylate ligand

A new zinc compound, together with a corresponding series of Zn-4f heterometallic coordination polymers, namely, [Zn(H2PBDA)(PBDA)]n (1), {[Ln2(PBDA)2·2H2O] [Zn2(PBDA)2Cl2]}n [H2PBDA = 3-(pyridin-3-yl-oxy) benzene-1,2-dicarboxylic acid, and Ln = Pr(2), Nd(3), Eu(4), Gd(5), Dy(6), Ho(7), Er(8)] have been hydrothermally synthesized and characterized systematically. Polymers 2-8 feature two-dimensional (2D) 4,4 networks, containing the original 1D heterometallic double stranded chains composed of [Ln2Zn2(PBDA)2] entities. The extensive hydrogen bonding and π-π stacking interactions were observed to stabilize the extended architectures. The luminescence emission spectra of the polymers vary depending on the lanthanide(III) ion present. Informative magnetic susceptibility measurements show that the same carboxylate bridging fashion of the PBDA ligand results in the different magnetic properties occurring within the heterometallic coordination polymers. In addition, polymer 6 exhibits an interesting slow magnetic relaxation behavior at lower temperatures.

A series of homonuclear lanthanide complexes incorporating isonicotinic based carboxylate tectonic and oxalate coligand: structures, luminescent and magnetic properties

A new family of five new lanthanide–organic frameworks incorporating both substituted isonicotinic acid and an oxalate coligand, have been fabricated successfully through a solvo-thermal reaction, namely, {[Ln(μ2-H2minca)](μ2-C2O4)·2H2O]·mH2O}n, (Ln = Sm (1), m = 0; Eu (2), m = 1; Gd (3), m = 1; Tb (4), m = 0; Ho (5), m = 0), (H3minca = 2-(hydroxyl)-6-methyl-isonicotinic acid, H2C2O4 = oxalate acid). Complexes 1–5 are isomorphous and isostructural, and they all exhibit two dimensional (2-D) corrugated networks with 63 topology, in which {LnO8} polyhedra are linked through carboxylate and oxalate groups into a net-like sheet. The luminescence emission spectra of the complexes vary depending on which lanthanide(III) ion is present. The H2minca ligand provides efficient energy transfer for sensitization of the Eu(III) and Tb(III) complexes. Variable temperature magnetic susceptibility measurements show that compound 3 displays weak anti-ferromagnetic interactions. The magnetic behaviors of 1, 2, 4 and 5 are ascribed to the depopulation of the Stark levels and weak antiferromagnetic interactions within the lanthanide(III) complexes.

Syntheses, structures and photoluminescence of Zn(II), Ag(I), Cu(I) and Co(II) coordination polymers of a tetrapyridyl ligand

The coordination of Zn(II), Ag(I), Cu(II), Cu(I) and Co(II) salts with N,N,N′,N′-tetrakis(4-pyridyl)-1,4-phenylenediamine (L) generated seven novel supramolecular coordination assemblies, {[CuI6L3Cl6]·3MeCN}n (1), {[CuI2LCl2]·2DMSO}n (2), {[CuILI]}n (3), {[Zn2L(HCOO)4]}n (4), {[Ag4L2(N3)4]·2H2O}n (5), {[Co4L2(SO4)4(H2O)12]·2CH3CN}n (6) and {[CuL(CH3COO)2(H2O)2]·2MeOH}n (7). In complexes 1 and 2, the Cu(II) atoms have been converted to Cu(I). Complexes 1, 4 and 5 show 1D or 2D coordination structures, and all of them are further linked by π⋯π stacking interactions to afford 3D structures. Complex 2 has a 2D structure composed of Cu2Cl2 units and L ligands. Complex 3 exhibits a doubly interpenetrated 3D structure. In complex 6, the 2D coordination networks are further linked by hydrogen bonds to afford a 3D supramolecular structure. Similar to complex 6, the 1D chains in complex 7 are assembled into a 2D network through hydrogen bonds. Based on the novel structures, the solid state luminescent properties of the complexes were investigated and discussed.

Mono-, Tetra- and octanuclear transition metal complexes of in situ generated schiff base ligands containing up to 12 coordinating atoms: syntheses, structures and magnetism

By the reaction of an alkoxyl containing tetraamine, 1,3-bis[(2-aminoethyl)amino]-2-propanol, with various aldehydes, O-vanillin and 2,6-diformyl-4-cresol, in the presence of various metal cations, four novel complexes were synthesized and structurally characterized. Complexes [CoHL1](ClO4)·2MeOH (1) and [NiH2L2](ClO4)2·0.5MeOH (2) have mononuclear structures, with the linear di-Schiff base ligand (HL1)2− and mono-Schiff base ligand H2L2 generated from in situ reactions under various pH conditions. In complexes [Ni4L3(SCN)3(MeOH)]Cl·2.5MeOH (3), and [Cu8(H2L3)2(OH)4(ClO4)](SCN)6(ClO4)·8H2O (4), an interesting 32-membered dodecadentate macrocyclic ligand H4L3 comprising four Schiff base CN double bonds was generated by a “2+2” type condensation reaction between the tetraamine and the dialdehyde. Complex 3 has a tetranuclear Ni4 coordination structure with all 12 coordinating atoms of (L3)4− utilized for coordination, and the alkoxyl groups are deprotonated and coordinated in a bridging mode. Complex 4 exhibits an octanuclear Cu8 coordination structure, with a ClO4− bridging two tetranuclear [Cu4H2L3(OH)2]4+ moieties through four weak axial Cu–O coordination bonds. In complex 4, only 10 coordinating atoms of (L3)4− are utilized for coordination, with the two alkoxyl groups left neutral and noncoordinated. It is noteworthy that H4L3 has two long saturated chains in the molecule. Therefore, it has good flexibility and tends to have a nonplanar structure. Variable temperature magnetic data for 3 and 4 indicated the existence of antiferromagnetic interactions, which were discussed based on the structural results.