Microwave Synthesis, Spectral, Thermal and Electrical Properties of Some Metal Complexes Involving 5‐Bromosalicylaldehyde

Abstract

Microwave-assisted synthesis is a branch of green chemistry. The salient features of microwave approach are shorter reaction times, simple reaction conditions and enhancements in yields. Some new Schiff base complexes of Cr(III), Co(II), Ni(II) and Cu(II) derived from 5-bromosalicylaldehyde with 4-nitro-1,2-phenylenediamine (H2L1) have been synthesized by conventional as well as microwave methods. These compounds have been characterized by elemental analysis, FT-IR, FAB-mass, molar conductance, electronic spectra, ESR, magnetic susceptibility and thermal analysis. The complexes exhibit coordination number 4 or 6. The complexes are coloured and stable in air. Analytical data revealed that all the complexes exhibited 1:1 (metal: ligand) ratio. FAB-mass and thermal data show degradation pattern of the complexes. The thermal behavior of metal complexes shows that the hydrated complexes loses water molecules of hydration in the first step; followed by decomposition of ligand molecules in the subsequent steps. The solid state electrical conductivity of the metal complexes has also been measured. Solid state electrical conductivity studies reflect semiconducting nature of the complexes.

Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This “Green” Method?

“…Similar conditions and results were used in the reaction between 5-bromosalicylaldehyde and 4-nitro-1,2-phenylenediamine (thermal reaction in refluxing MeOH, 6 h, 73% yield vs. MW irradiation in EtOH, 5-6 min, 91% yield) and the 1:1 complexes obtained from the resulting Schiff base with Cr(III), Co(II), Ni(II), and Cu(II) (thermal reaction in refluxing MeOH, 7-10 h, 62-68% yield vs. MW irradiation in EtOH, 6-9 min, 79-85% yield) [71].…”

Alternative Technologies That Facilitate Access to Discrete Metal Complexes

“…Between 2010 and 2016, the Jain group described the microwave synthesis of different chromium complexes with Schiff base ligands which were further used for their antimicrobial properties. [Cr­(74)­(H 2 O) 3 ]­Cl , [Cr­(75)­Cl]·2H 2 O , [Cr­(78) 2 (H 2 O) 2 ]·Cl , [Cr­(80) 2 (H 2 O) 2 ]­Cl , [Cr­(84) 2 (H 2 O) 2 ]­Cl·2H 2 O , [Cr­(83)­(H 2 O) 3 ]­Cl 2 , [Cr­(88)­(H 2 O)­Cl] , [Cr­(81) 2 (H 2 O) 2 ]·Cl , [Cr­(82) 2 (H 2 O) 2 ]·Cl , [Cr­(85) 2 (H 2 O) 2 ]­Cl , and [Cr­(86) 2 (H 2 O) 2 ]­Cl were synthesized as follows. Chromium salt and ligand were ground together and then transferred into a reactor with 3–5 mL of dry EtOH to be heated under microwave irradiation (Table , entries 1–11; see Figure for ligand structure).…”

“…To control the temperature, microwave reactions were performed using on/off cycles. [Co­(84) 2 ]·2H 2 O , [Co­(83)­(H 2 O)]­Cl , [Co­(88)­(H 2 O) 2 ] , [Co­(81) 2 (H 2 O) 2 ] , [Co­(82) 2 (H 2 O) 2 ] , [Co­(85) 2 (H 2 O) 2 ]·H 2 O , [Co­(86) 2 (H 2 O) 2 ] , [Co­(78) 2 (H 2 O) 2 ] , [Co­(80) 2 (H 2 O) 2 ] , [Co­(76) 2 (H 2 O) 2 ]·Cl 2 , [Co­(77) 2 Cl 2 ].2H 2 O , [Co­(74)­(H 2 O) 3 ] , and [Co­(75)­Cl]·2H 2 O were synthesized as follows. Ligand and CoCl 2 ·6H 2 O were ground together in a stoichiometric ratio (1:1 or 2:1) before being transferred to a reactor with 3–5 mL of dry EtOH and heated under microwave irradiation for 6–8 min (Table , entries 1 to 13, see Figure for ligand structures).…”

“…Microwave reactions were performed using on/off cycles to control the temperature. [Ni­(84) 2 ]·2H 2 O , [Ni­(83)­(H 2 O) 3 ]­Cl , [Ni­(88)]·2H 2 O , [Ni­(81) 2 (H 2 O) 2 ] , [Ni­(82) 2 (H 2 O) 2 ] , [Ni­(85)]·3H 2 O , [Ni­(86) 2 ]·2H 2 O , [Ni­(74)­(H 2 O) 3 ] , [Ni­(75)­Cl]·3H 2 O , [Ni­(76) 2 Cl 2 ]·2H 2 O , [Ni­(77) 2 Cl 2 ]·2H 2 O , [Ni­(78) 2 ]·2H 2 O , [Ni­(80) 2 (H 2 O) 2 ] , [Ni­(69) 2 (H 2 O) 2 ]­Cl 2 , and [Ni­(70) 2 ] (Table , entries 2–16) were synthesized using a similar procedure. Before performing microwave irradiation, the appropriate ligand and NiCl 2 ·6H 2 O were ground in a stoichiometric ratio (1:1 or 2:1).…”

“…Syntheses were performed in an open glass vessel using a modified microwave oven model 2001 ETB with a rotating tray and a microwave energy output of 800 W. Microwave reactions were performed using on/off cycling to control the temperature. [Cu­(74)­(H 2 O)] , [Cu­(75)­Cl]·2H 2 O , [Cu­(76) 2 Cl 2 ]·2H 2 O , [Cu­(77) 2 Cl 2 ]·2H 2 O , [Cu­(88)]·2H 2 O , [Cu­(78) 2 ]·2H 2 O , [Cu­(80) 2 ] , [Cu­(69) 2 (H 2 O) 2 ]­Cl 2 , [Cu­(70) 2 ] , [Cu­(81) 2 ] , [Cu­(82) 2 ]·2H 2 O , [Cu­(84) 2 ]·2H 2 O , [Cu­(83)­(H 2 O)]­Cl , [Cu­(85) 2 ]·2H 2 O , and [Cu­(86) 2 (H 2 O) 2 ] (Table , entries 2 to 16, see Figure for ligand structures) were synthesized using a similar procedure. Before microwave irradiation, the ligand and [CuCl 2 ]·2H 2 O were ground in a stoichiometric ratio of 1:1 or 2:1.…”