Influence of Ligand Substitution Pattern on Structure in Cobalt(II) Complexes of Bulky N,N′‐Diarylformamidinate N‐Oxides

Abstract

Cobalt(II) complexes of bulky N,NЈ-diarylformamidinate Noxide ligands were synthesized and structurally characterized. The cobalt(II) bis(chelates) are square-planar (low spin) in the solid state, according to XRD and magnetic measurements (μ eff = 1.8 to 2.1 μ B ), but show square-planar (low spin) to tetrahedral (high spin: μ eff = 3.5 to 4.7 μ B ) isomeriza-

Electro‐ and Photocatalytic Generation of H2 Using a Distinctive CoII “PN3P” Pincer Supported Complex with Water or Saturated Saline as a Hydrogen Source

“…[40] Importantly,amajority of these complexes requiret he presenceo fa cids as the sourceo fh ydrogen in order to electrocatalytically produce H 2 in polar organic solvents. [50][51][52][53] Single crystalso f1 were obtained from CH 2 Cl 2 and X-ray diffraction analysisr evealed two independentm olecules in the structure with distorted square-based pyramidal geometry at Co and with nearly identical bondingp arameters as shown in Scheme 1( Figure S1, Table S2, S3). [8,11,[41][42][43] Cobalt-basedelectrocatalysts that use watero rm ixed organic/water solutions as the hydrogen sourceoperate in the voltage range of À1.5 to À2.0 Vvs.…”

“…[50][51][52][53] Single crystalso f1 were obtained from CH 2 Cl 2 and X-ray diffraction analysisr evealed two independentm olecules in the structure with distorted square-based pyramidal geometry at Co and with nearly identical bondingp arameters as shown in Scheme 1( Figure S1, Table S2, S3). The targeted molecular formula was supported by microanalysis and ar oom temperature magneticm oment of 2.4 m B ,w hich indicatedap aramagnetic low spin Co II center.…”

Geometry and Spin Change at the Heart of a Cobalt(II) Complex: A Special Case of Solvatomorphism

“…[b] Theory level: uB3LYP/LANL2DZ, PCM: CH 2 Cl 2 . [c] 2 – 4 : Co(L) 2 , L=amidine‐oxide‐type 7. [d] Compound 5 : Co(L) 2 , L=triazene 1‐oxide‐type (GESTED) 20.…”

“…For specific d n metal configurations (d 3 , d 4 , d 6 , d 7 ) in four‐coordinated ligand environments, it was established that both square‐planar and tetrahedral geometries are possible 1a. b More specifically, for cobalt(II) d 7 bis(chelates), the configurational equilibrium between square planar and tetrahedral forms was previously reported for several ligand types: β‐ketoamines,3 iminopyrrolyl,4 α‐imino alkoxides,5 triazene 1‐oxides,6 and amidine N ‐oxides (AMOXs) 7. These systems exhibit not only stereoisomerism but also spin isomerism from high‐spin (HS), tetrahedral cobalt(II) complexes ( S =3/2) to low‐spin (LS), square‐planar cobalt(II) complexes ( S =1/2),2d, e, 8 although a few exceptions exist 9.…”

“…The square‐planar form is usually observed in the solid state, whereas the tetrahedral form (or an equilibrium between the two forms) is found in solution of non‐coordinating solvents. In all such systems, the specific geometry/ spin‐state combination in the ground state was shown to be mainly determined by the properties of the ligand, and to be particularly sensitive to the ligand‐substitution pattern 3–7. However, within a given metal complex, factors other than those directly linked to the metal and/or the ligand have to be considered: reaction conditions, solvent, temperature, and secondary interactions.…”