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Abstract

New copper(II) complexes of asymmetrical tetradentate Schiff bases containing pyrazine have been prepared and thoroughly characterised by elemental analysis, IR and electronic spectroscopy, mass spectrometry and magnetic measurements. Two alternative methods were used in the isolation of the complexes: template synthesis in the preparation of Cu(SalDpyz)ClO 4 (HSalDPyz = derived from the condensation of salicylaldehyde, acetylpyrazine and 1,2ethylendiamine, 2-methyl-1,2-propylendiamine, 1,2-phenylendiamine) and direct interaction between copper perchlorate and the corresponding Schiff base, as in the isolation of Cu (AEPyz)(ClO 4 ) (HAEPyz = (Z)-4-[2-{[2-{[(E)-1-(pyrazinyl)ethylidene]amino} ethyl)amino]-3-penten-2-one)]. [Cu(SalEn)(py)(OClO 3 )][Cu(SalEn)(py)]ClO 4 (1) (SalEn = 4-(2-hydroxyphenyl)-3-aza-3-buten-1-amino, py = pyridine), metal precursor in the preparation of Cu(SalEnpyz)(ClO 4 ) (HSalEnpyz = 2-{E(2-{[(E)-1-(2-pyrazinyl)ethylidene]amino}ethyl)imino]methyl}phenol), was crystallographically characterised. The crystal structure of [Cu(AEpyz)]ClO 4 (2) is also reported.

Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

“…planes is very low in all cases (<0.07 Å). Coordination distances and angles are comparable to those of other copper compounds with N 2 O tridentate Schiff base ligands and pyridine as the forth ancillary ligand [77,79].…”

When the Metal Makes the Difference: Template Syntheses of Tridentate and Tetradentate Salen-Type Schiff Base Ligands and Related Complexes

“…Copper (II) has revealed to be a very versatile and efficient templating metal ion for obtaining tridentate N 2 O half units, and several approaches have been described for the last four decades. The first method here described employs an auxiliary monodentate ligand L' in the reaction process to isolate the mononuclear complexes of general formula [Cu( G L)(L')](X) (X -= anion) [39,53,[62][63][64][65][66][67][68][69][70]. The reaction occurs at room temperature in methanol, and the sequence of addition of the reagents in the reaction mixture is fundamental, usually entailing copper(II) salt, G-salH, and L' first in a 1:1:3 ratio, and then the aliphatic diamine.…”

“…The auxiliary ligands L' usually employed are pyridine (py) [39,53,62,63,65,66,[68][69][70], imidazole (imH) [62,66], and piperidine (pip) [67,69], while the copper(II) salts are nitrate [62,63] or perchlorate [39,53,62,63,65,66,[68][69][70]. The py/ClO 4 combination is among the most applied since it probably ensures the highest purity and yield of the isolated products.…”

“…This method revealed to be very versatile in terms of the variability of the substituent on the G-salH and its position on the aromatic ring. Unsubstituted H-salH has been mainly employed [39,62,65,66], but the presence of electron withdrawing (5-NO 2 [39,63,68]) or releasing 67,69], 5-OMe [39]) groups is also well tolerated by this synthetic path. The aliphatic diamine can also vary from en [39,53,62,63] to tn [39], 2-methyl-1,2diaminopropane (pn) [53,65], 2,2,-dimethyl-1,3-diaminopropane [67,69], and the chiral chxn and diphenylethylendiamine (dpen) [67][68][69][70].…”

“…The efficacy of this method, which takes advantage of the thermodynamic template effect [67], relies on two features: (i) copper prefers a square planar geometry, and (ii) the ancillary ligand L' can saturate the coordination sites in the intermediate [Cu(G-sal)(L') 2 ] + in solution and in the final product [Cu( G L)(L')](X) in the solid state to ensure such a coordination environment (Figure 2). Indeed, the crystal structure of several derivatives has been obtained during the years [39,[65][66][67][68]70], and all of them show the copper(II) ion surrounded by the N 2 O ligand G Land a molecule of auxiliary ligand L' in the equatorial plane. The Cu-O bond distances usually settle around 1.90 Å, while the Cu-N ones are usually longer and depend on the nitrogen atom involved.…”