6533b853fe1ef96bd12acad2

RESEARCH PRODUCT

A linear open-chain piperazine-pyridine ligand and its meso-helical Co complex

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Abstract An oligomeric ligand (HPPy) 2 P, N , N ′-bis[2-(6-( N -( N ′-(2-hydroxyethyl)piperazinyl)methyl)]piperazine, was designed to resemble structurally open-chain aza-crowns. Owing to the all- trans configuration of piperazine and pyridine free electron pairs, it should adopt a near linear overall structure in solvent. Theoretical calculations at ab initio level confirm the overall linear structure of free ligand. The crystal structure of the complex [(HPPy) 2 P][Co(NO 3 ) 2 ] 2 shows a contraction from ∼3 to 2 nm structure. Each coordination site creates either a Δ or Δ configuration around the metal ion, thus causing a ligand with an even number of coordination centres to be meso -helical. The complex (C 30 H 48 N 12 O 14 Co 2 ) crystallizes in the monoclinic space group P 2 1 / n (No. 14) with the cell dimensions a = 11.673(4), b = 13.212(8), c = 12.561(7) A , β = 90.33(1)°, V = 1937(2) A 3 and Z = 2 . The structure is refined to a final agreement factor R ( F 0 2 ) = 0.0576 using 2121 reflections with l >4 σ ( l ). The molecule is centrosymmetric with two identical coordination centres, in which the regular octahedral geometry is tetragonally distorted.