A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N2O2 type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H2L4 and its corresponding complex VOL4 were determined by X-ray crystallography.

Synthesis, crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A pair of stereoisomers of nickel Schiff base complexes, namely [Ni(C17H15N4O2)2·2CH3OH]n (1) (C17H15N4O2 = 2-acetylpyrazine-l-tryptophan) and [Ni(C17H15N4O2)2·2CH3OH]n (2) (C17H15N4O2 = 2-acetylpyrazine-d-tryptophan), were synthesized and characterized by physico-chemical and spectroscopic methods. The X-ray diffraction single-crystal analyses indicate that the structure of 2 is essentially 0D monomeric, while a 2D layer structure is formed through N–H…O intermolecular hydrogen bonds for 1. The interactions between complex 1 and calf thymus DNA were investigated by spectroscopic and viscometric methods. The results indicate that complex 1 interacts with DNA very strongly (K
 b = 1.01 × 107 mol−1 L and K
 sq = 1.11). The nature of the binding seems to be mainly an electrostatic interaction between DNA and the complex. However, other binding modes, such as hydrogen bonding, may also be present in this system.

Nickel(II) complexes with Schiff bases derived from 2-acetylpyrazine and tryptophan: synthesis, crystal structures and DNA interactions

Two dinuclear succinato-bridged nickel(II) complexes [Ni(RR-L)]2(μ-SA)(ClO4)2 (1) and [Ni(SS-L)]2(μ-SA)(ClO4)2 (2) (L = 5, 5, 7, 12, 12, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradecane, SA = succinic acid) were synthesized and characterized by EA, Circular dichroism (CD), as well as IR and UV/Vis spectroscopy Single crystal X-ray diffraction analyses revealed that the NiII atoms display a distorted octahedral coordination arrangement, and the succinato ligand bridges two central NiII atoms in a bis bidentate fashion to form dimers in 1 and 2 The monomers of {[Ni(RR-L)]2(μ-SA)}2+ and {[Ni(SS-L)]2(μ-SA)}2+ are connected by O–H···O and N–H···O hydrogen bonds into a 1D right-handed and left-handed helical chain along the b axis, respectively The homochiral natures of 1 and 2 are confirmed by the results of CD spectroscopy

Synthesis and Crystal Structure of Two Succinato-Bridged Macrocyclic Nickel(II) Complexes

The reactions of a racemic four-coordinate Ni(II) complex [Ni(rac-L)](ClO4)2 with l- and d-alanine in acetonitrile/water gave two six-coordinate enantiomers formulated as [Ni(RR-L)(l-Ala)](ClO4)·2CH3CN (1) and [Ni(SS-L)(d-Ala)](ClO4) (2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane, Ala− = alanine anion), respectively. Evaporation from the remaining solutions gave two four-coordinate enantiomers characterized as [Ni(SS-L)](ClO4)2 (S-3) and [Ni(RR-L)](ClO4)2 (R-3), respectively. Single-crystal X-ray diffraction analyses of complexes 1 and 2 revealed that the Ni(II) atom has a distorted octahedral coordination geometry, being coordinated by four nitrogen atoms of L in a folded configuration, plus one carboxylate oxygen atom and one nitrogen atom of l- or d-Ala− in mutually cis-positions. Complexes 1 and 2 are supramolecular stereoisomers, constructed via hydrogen bonding between [Ni(RR-L)(l-Ala)]+ or [Ni(SS-L)(d-Ala)]+ monomers to form 1D hydrogen-bonded zigzag chains. The homochiral natures of complexes 1 and 2 have been confirmed by CD spectroscopy.

Chiral resolution of l- and d-alanine and a racemic macrocyclic nickel(II) complex: synthesis and crystal structures

Five three-dimensional (3D) coordination polymers, {(NiL)[(NiL)(V16O42)]}n·2nH2O (1), [(NiL)3(VO3)6]n·5nH2O (2), [(NiL)3(V6O18)]n·7nH2O (3), [(NiL)3(V8O23)]n (4), and [(NiL)4(V10O29)]n (5), have been obtained by the reaction of the macrocyclic nickel complex [NiL](ClO4)2 (L = 1,4,8,11-tetraazacyclotetradecane) with NH4VO3 under different conditions. Single-crystal X-ray diffraction analyses revealed that the [VO3]– anion assumes diverse species and structures in these five coordination polymers, including the [V16O42]n4n– sheet, [V6O18]6– ring, [VO3]nn– chain, [VO3]nn– sheet, and [V10O29]n8n– chain. The [V16O42]n4n– sheets, [V6O18]6– rings, [VO3]nn– chains, [VO3]nn– sheets, and [V10O29]n8n– chains are linked together through [NiL]2+ bridges to form the 3D frameworks of 1–5. The single-crystal to single-crystal transformation between 2 and desolvated 2 was successfully realized. Electrochemical measurements indicate that 2 and 4 are potential catalysts for water splitting.

Vanadium Polyoxoanions within Coordination Polymers Based on a Macrocyclic Nickel Complex: Structural Diversities and Single‐Crystal to Single‐Crystal Transformation

Three dinuclear terephthalato-bridged nickel(II) complexes [Ni(rac-L)]2(μ-TPA)(ClO4)2 (1), [Ni(RR-L)]2(μ-TPA)(ClO4)2 (2), and [Ni(SS-L)]2(μ-TPA)(ClO4)2 (3) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, TPA = terephthalic acid) have been synthesized and characterized. Single-crystal X-ray diffraction analyses revealed that the Ni(II) atoms have six-coordinated distorted octahedral environments, and the terephthalato ligand bridges two Ni(II) centres in a bis bidentate fashion to form dimers in all three complexes. The monomers of {[Ni(RR-L)]2(μ-TPA)}2+ and {[Ni(SS-L)]2(μ-TPA)}2+ are connected through intermolecular hydrogen bonds to generate 1D right-handed and left-handed helical chains, respectively. The racemic character of 1 and the homochiral natures of 2 and 3 are confirmed by the results of CD spectroscopy.

Synthesis and crystal structures of terephthalato-bridged macrocyclic nickel(II) complexes with cis configurations

The reactions of transition metal macrocyclic complexes [ML](ClO4)2 (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, M = Ni, Cu) with NH4VO3 under hydrothermal conditions gave two coordination polymers, namely [NiL]2[V6O17] and [CuL]2[V6O17]. Single-crystal X-ray diffraction analyses indicated that the central Ni(II)/Cu(II) atom displays a distorted six-coordinate octahedral coordination geometry by coordination with four nitrogen atoms of L, and two oxygen atoms of [VO4] tetrahedrons. Compounds [NiL]2[V6O17] and [CuL]2[V6O17] show three-dimensional structures, which are constructed through the connections of dodecanuclear [V12O32]4− rings with [NiL]2+ in [NiL]2[V6O17], and [V8O22]
 n
 4n−
 chains with [CuL]2+ in [CuL]2[V6O17], respectively, generating one-dimensional channels.

Xian-You Yuan

Papers

Synthesis and crystal structures of terephthalato-bridged macrocyclic nickel(II) complexes with cis configurations

Synthesis and crystal structures of two three-dimensional vanadium polyoxoanion-bridged macrocyclic metal complexes