We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.
The trinuclear nickel(II) complex [Ni3(saltagtBu)(bpy)3(H2O)3]Cl (H5saltagtBu = 1,2,3‐tris[(5‐tert‐butylsalicylidene)amino]guanidine) was synthesized and characterized by experimental as well as theoretical methods. The complex salt crystallizes with three molecules of dimethylformamide (dmf) and water as [Ni3(saltagtBu)(bpy)3(H2O)3]Cl·3dmf·3H2O (1) in the trigonal space group P3, with the complex located on a threefold rotation axis, which is consistent with the molecular C3 symmetry of the complex cation. Magnetic measurements reveal an antiferromagnetic coupling (J = –35.9 cm–1) between the nickel(II) ions leading to a diamagnetic ground state for the trinuclear complex cation. Theoretical investigations based on broken‐symmetry DFT confirm the antiferromagnetic exchange within the complex cation of 1. Additional single‐ion CASSCF ab initio studies reveal that magnetic anisotropy is present in the system. The experimental and theoretical results for 1 are compared with those of a structurally similar nickel(II) complex that is based on the bromo‐substituted derivative of the triaminoguanidine ligand. The differences in their magnetic properties can be attributed to the stronger elongation of the pseudo‐octahedral coordination sphere at the nickel(II) centers in case of 1. The analysis of the magnetic properties of 1 clearly shows that for such exchange coupled systems reliable parameters for the magnetic anisotropy cannot be extracted from experimental data alone.
A new synthesis of push-pull pyrroles of type 5 was developed starting from bis(imidoyl chlorides) 1 and various iminodiacetic acid derivatives 3. The use of appropriate N-trifluoroacetyl residues as protecting/activating group proved to be the method of choice for the straightforward preparation of the 3,4-diarylamino-1H-pyrroles 5. When benzothiazole substructures are present in 2,5-position of heterocycles 5, a two-
Pyrrole derivatives R 0120A New Synthesis of Push-Pull Pyrroles, Their Oxidation to Stable 3H-Pyrroles and an Unexpected Anellation Reaction. -The reaction of bis-imidoyl chlorides with iminodiacetic derivatives under conditions A) affords pyrrole products. The choice of an N-trifluoroacetyl group [cf. (VI)] allows the direct synthesis of products (VIII) without any need of deprotection. The latter are easily oxidized to 3H-pyrroles (IX), while starting from (IV) the same procedure leads to the novel 3H-pyrrolo[3,4-b]quinoxalines (V). -(BUEHRDEL, G.; BECKERT*, R.; HERZIGOVA, P.; PETRLIKOVA, E.; SCHUCH, D.; BIRCKNER, E.; GOERLS, H.; Eur.
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