ic0501420_si_001.cif (17.78 kB)
Copper(II) Mediated Anion Dependent Formation of Schiff Base Complexes†
dataset
posted on 2005-05-30, 00:00 authored by Sachindranath Pal, Anil Kumar Barik, Samik Gupta, Arijit Hazra, Susanta Kumar Kar, Shie-Ming Peng, Gene-Hsiang Lee, Ray J. Butcher, M. Salah El Fallah, Joan RibasA tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been
investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation
of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each
of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X
= ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16- tetraza-5,10,15,20- tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X·H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also
produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2]·H2O [X =
Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper
atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and
N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal
geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore,
where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature
(300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between
the metal centers, viz., Cu(1)···Cu(2), Cu(2)···Cu(2A), and Cu(2A)···Cu(1A) are 3.858, 3.89, and 3.858 Å,
respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the
spin centers. The exchange coupling constants between Cu(1)···Cu(2) and Cu(2)···Cu(2A) centers have turned
out to be −305.3 and −400.7 cm-1, respectively, resulting in a S = 1/2 ground state. The complexes are further
characterized by UV−vis, IR, electron paramagnetic resonance, and electrochemical studies.