Hydrothermal Syntheses and Structural Diversity of Cobalt Complexes with 2,2′-Bibenzimidazole Ligand by Temperature Tuning Strategy

Abstract

Five different cobalt complexes were synthesized by the combination of the multidentate ligand 2,2′-bibenzimidazole (H 2 bbim) and the coordination plasticity of cobalt ion in the presence of 4-cyanopyridine under hydrothermal conditions using temperature as the only independent variable. The structural features of theses complexes, which ranged from zero-dimensional (0D) in [Co(Hbbim) ] n (4), were extremely dependent on the reaction temperature. At 130 °C, discrete 1 was the unique product. However, 4 was the main product when the reaction temperatures were set in the range of 160-200 °C. 2 and 3 yielded at 140 °C as main products. In spite of the structural diversity of this system, crystallographic studies reveal that the H 2 bbim ligand typically displays tridentate (Hbbim -) and/or tetradentate (bbim 2-) coordination modes at high temperature, however, a chelating mode at low temperature. The ligands Hbbimand bbim 2offering donor atoms and charge balance may have both advantages of bipyrimidine and oxalate in the assembly of high-dimensional structures. Indeed, 2 is the first instance of 2D honeycomb (6,3), neutral coordination polymer constructed by only one type of ligand and one type of metal ion. Magnetic properties of 3 and 4 have been studied in the temperature range of 2-300 K. Both compounds exhibit antiferromagnetic interactions between metal ions through the bridging ligand.

Syntheses, Crystal Structures, and Spectral Properties of Two Coordination Compounds Based on 1,2-Bis(benzimidazolyl)benzene

“…9 The control of dimensionality of the complexes, however, is still an arduous challenge to chemists, because the final structures are always influenced by various factors. 10 It is well known that the coordination mode of ligand is to a certain extent the key factor that can determine the final structural dimensionalities of the compounds. Change of the organic ligand, such as the length, flexibility and conformational preference can result in a remarkable class of complexes bearing diverse architectures and functions.…”

Two 2D metal–organic frameworks based on 2,2′-bibenzimidazole ligand with (6,3) net topology

“…Different from other benzimidazole derivates, 2,2′-bibenzimidazole(H 2 bbim) contains two contiguous benzimidazole groups and has multiple nitrogen-donor sites. H 2 bbim is a good bridging ligand for constructing novel MOFs because of its multiplicate coordination modes and strong coordination ability to metal ions [8]. It can be served as a neutral bidentate ligand (H 2 bbim), also can be deprotonated in basic condition and served as a tridentate (Hbbim − ) or tetradentate ligand (bbim 2− ).…”

“…Furthermore, different metal ions with different coordination plasticities can generate diverse structures [9]. Quite a few complexes of H 2 bbim with transition metal ions have been prepared [10], but two-dimensional and threedimensional frameworks formed by unique H 2 bbim and metal ions have rarely been reported [8]. Herein, we wish to report two novel 2D metalorganic frameworks with different coordination geometry, {[Zn 4 (Hbbim) 4 (bbim) 2 ]·2H 2 O} n (1) and [Cd 2 (Hbbim) 2 (bbim)] n (2) [11].…”

“…Zn(1) ion is coordinated by four nitrogen atoms from two chelating bbim 2− ligands and one nitrogen atom from one Hbbim − ligand, while Zn(2) ion is coordinated by two nitrogen atoms from one chelating bbim 2− ligand, two nitrogen atoms from one chelating Hbbim − ligand and one nitrogen atom from one Hbbim − ligands. The apical sites of the two trigonal bipyramids are occupied by N (8), N(22) and N(3), N(6), respectively. Compared to the equatorial Zn-N distances (range from 1.966 (8) (4) ion is four-coordinated by two nitrogen atoms from a chelating bbim 2− ligand and two nitrogen atoms from two Hbbim − ligands.…”

“…Zn(3) ion exhibits a distorted octahedral coordination geometry by coordinating to six nitrogen atoms from three chelating Hbbim − ligands. The Zn-N bond distances range from 2.104(8) to 2.225(8) Å, and the N-Zn-…”