Binickel(II) complex of a new asymmetrical acyclic ligand: the X-ray crystal structure of [Ni 2L](ClO 4) 2 reveals alternating square-planar and octahedral nickel ions

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The binuclear nickel(II) complex of the macrocyclic ligand H 2L which contains one N(CH 2) 2N and one N(CH 2) 2NH– moiety has been studied. In the mixed spin-state complex [Ni 2L][ClO 4] 2 ( 1), one nickel center is square-planar (low spin), accommodated by the smaller N 2O 2 cavity provided by the phenolic oxygens and N(CH 2) 2N nitrogens; the other nickel center is octahedral (high spin), accommodated by the larger cavity provided by the phenolic oxygens and N(CH 2) 2NH– nitrogens. Diethylenetriamine takes the skew configuration, which inhibits the full cyclization. This leads to one primary amino nitrogen and one acetyl oxygen on both sides of the octahedral nickel completing the fifth and sixth coordination sites. The Pauling covalent radius of low-spin Ni 2+ is ca. 0.20 Å shorter than that of high-spin Ni 2+, leading to considerably stronger in-plane ligand-field strength of N 2O 2 donors at the square nickel(II) relative to that of the octahedral nickel(II). Crystallographic data for ( 1): space group P-1, triclinic, a=11.573(2) Å, b=15.608(3) Å, c=10.943(2) Å, α=104.54(2)°, β=114.97(1)°, γ=82.62(1)°, Z=2, R=0.061, R w=0.079.