Copper(II) mediated anion dependent formation of Schiff base complexes

A 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 (1,3DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand Complex [CU4(L-1)(2)(L-2)(2)(NO3)(2)] (1), where 1-12L, = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl3-(5-hyd roxyhexahydro-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)X-2 (X = ClO4, NO3, BF4 (2)) (T(3-)porphyrinogen = 1,6,11,16- tetraza-5,10,15,20- tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X](XH2O)-H-. (X = Cl (3), Br (4)), The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)(2)]X-2 [X = CLO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X-2]center dot 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 N-5 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 A, 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.