Structural variation and magnetic properties of tetrakis (μ2-carboxylate) -bridged dicopper (II) complexes of betaines with different axial ligands

Abstract Three tetrakis ( μ 2 -carboxylate) -bridged dicopper (II) complexes of betaines, [Cu 2 (pybet) 4 (H 2 O) 2 ] (NO 3 ) 2 (ClO 4 ) 2 · 2H 2 O (pybet = pyridinioacetate, C 5 H 5 N + CH 2 CO − 2 , pybet) (1) , [Cu 2 (pybet) 4 (H 2 O) Cl] (ClO 4 ) 3 · 2H 2 O (2) and [Cu 2 (ppbet) 4 Cl 2 ] (ClO 4 ) 2 (ppbet = pyridiniopropionate, C 5 H 5 N + CH 2 CH 2 CO − 2 ) (3) , have been synthesized and characterized by X-ray crystallography. These complexes all comprise [Cu 2 ( μ 2 -carboxylate) 2 ] structures (Cu· · ·Cu = 2.677 (1) –2.760 (1) A) with each copper (II) atom being coordinated in a square-pyramidal CuO 4 L environment, in which the axial ligands (L) are two aqua molecules (Cu — O = 2.093 (2) A) , one aqua molecule and one chloride ion (Cu — O = 2.130 (8) , Cu — Cl = 2.358 (4) A) and, two chloride ions (Cu — Cl = 2.454 (2) A) in complexes 1, 2 and 3, respectively. The intramolecular Cu· · ·Cu distance may correlate to the mutual repulsion between the axial and basal metal-ligand bonds. Temperature-dependent magnetic susceptibility data of the powder samples of the complexes have been fitted, yielding the intramolecular coupling constant 2 J values of −340, −321 and −301 cm −1 for 1, 2 and 3, respectively. The magnitudes of 2 J may be inversely correlated to the displacement of the metal atom from the basal plane.