Synthesis, characterization, and use of a cobalt(II) complex as an NMR shift reagent: An integrated laboratory experiment

Abstract

A currently popular approach to advanced undergraduate laboratory organization involves integration of materia! from the various disciplines of chemistry. All too often, however, the integrated laboratory is composed only of standard experiments randomly selected from the individual disciplines. A recent laboratory manual entitled "Integrated Experimental Chemistry," in fact, follows this route {1). An approach which is seemingly more relevant to the usual research situation involves integration of diverse chemical concepts into each experiment. The typical organization is thus: synthesis -* analysis -* physical measurement. A paucity of such experiments are available.The following experiment was designed for and has been employed in our majors junior-level integrated laboratory. Approximately four 3-hr laboratory periods are required for completion, assuming ready access to instruments. The acetylacetonate complex of cobalt(II), Co(AcAc)2(H20)2, is prepared and isolated following modification of literature methods (2). Spectrophotometric analysis of the cobalt content serves to characterize the material. Additional characterization by a method(s) of the student's choice provides an open-ended dimension to the experiment. The paramagnetic complex is further employed as an NMR shift reagent to simplify the spectrum of a complex alcohol. SynthesisA large number of metal complexes have been prepared using ,3-diketone compounds (3). Complexes of acetylacetone (2,4-pentane-dione) with first row transition metal ions are rather easily prepared and are of considerable importance in analytical and inorganic chemistry. The sodium salt of acetylacetone is prepared and this adduct is allowed to react with an aqueous cobatt(ll) chloride solution:

XAS examination of glutathione–cobalt complexes in solution

“…The proton chemical shifts of the resulting complexes and free GSH are summarized in Table 3. Usually, the presence of a paramagnetic metal ion, like Co(II), induces an important field shifting [55,56], whereas in diamagnetic compounds, like Co(III), some small modifications of chemical shifts are expected for protons near the complexation center [57]. Starting from CoCl 2 , 6H 2 O or [Co(NH 3 ) 6 ]Cl 3 , similar spectra were obtained, exhibiting small modifications of proton chemical shifts of GSH (Table 3), together however with important broadening of signals due to the complexation phenomenon.…”

Synthesis and Coordination Behaviour of a Novel Tridentate P,N,O‐Ketiminate Ligand

“…All reactions were performed under argon atmosphere using Schlenk techniques. The compounds 3-formylacetylacetone, [13] o-(diphenylphosphino)aniline, [30] [Fe(acac) 2 (TMEDA)] [31] and [Co-(acac) 2 ] [32] were prepared according to literature methods. IR spectra were measured with a Bruker Tensor 27 spectrometer equipped with a diamond ATR unit.…”

Predicting Supramolecular Connectivity of Metal-Containing Solid-State Assemblies using Calculated Molecular Electrostatic Potential Surfaces

“…Starting complexes [Co­(acac) 2 (H 2 O) 2 ] ( 1 ), [Ni­(acac) 2 (H 2 O) 2 ] ( 2 ), [Cu­(acac) 2 ] ( 3 ), [Co­(hfac) 2 (H 2 O) 2 ] ( 4 ), [Ni­(hfac) 2 (H 2 O) 2 ] ( 5 ), and [Cu­(hfac) 2 (H 2 O) 2 ]·H 2 O ( 6 ) were synthesized following a modified procedure of a literature reports. , …”

“…6) were synthesized following a modified procedure of a literature reports. 42,43 The complexes 1a−6b were prepared by mixing an ethanol solution (10 mL) of starting metal complex (1−6) with the ethanol solution (10 mL) of ligand (4(3H)-pyrimidinone, 4-pym, or 4(3H)quinazolinone, 4-quz). The resulting mixture was continuously stirred and heated under reflux for 2 h. Solution was then cooled and left standing at room temperature to slowly evaporate.…”