A New Class of Biomimetically Relevant “Scorpionate” Ligands. 2. The (2-Hydroxyphenyl)bis(pyrazolyl)methanes: Structural Characterization of a Series of Mono-, Di-, and Trinuclear Nickel(II) Complexes

The preparation of a new class of mixed functionality biomimetic ligand, (2-hydroxyphenyl)bis(pyrazolyl)methane, L1, (2-hydroxyphenyl)bis(3,5-dimethylpyrazolyl)methane, L2, and (2-hydroxyphenyl)bis(3-isopropylpyrazolyl)methane, L3, is described. These ligands were used to synthesize the nickel(II) complexes, [Ni(L1) 2 ], 1 ·MeCN; [Ni(L2) 2 ], 2 ·0.5MeOH and 2 ·2H 2 O; [Ni(μ-L2) 2 NiCl 2 ], 3 ·2H 2 O and 3 · 2 CH 2 Cl 2; [Ni 3 (μ 3 -Cl) 2 (μ-L3) 2 (L3)(MeOH)]Cl, 4 ·MeOH·4H 2 O and 4 ·MeOH·1.42 i Pr 2 O; and [Ni 3 (μ 3 -OH) 2 (μ-L3) 3 ][BF 4 ], 5 and 5 ·2Me 2 CO. X-ray crystal analysis of 1 − 5 gave the following structural parameters: 1 ·MeCN, C 28 H 25 N 9 NiO 2, triclinic, a = 10.600(3) Å, b = 11.371(3) Å, c = 12.194(3) Å, α = 71.17(2)°, β = 94.69(2)°, γ = 83.04(2)°, space group P 1̄, Z = 2; 2 ·2H 2 O, C 34 H 42 N 8 NiO 4, monoclinic, a = 9.037(2) Å, b = 19.272(3) Å, c = 19.643(3) Å, β = 94.69(2)°, space group C2/c, Z = 4; 3 ·2CH 2 Cl 2, C 36 H 42 N 8 Cl 6 Ni 2 O 2, monoclinic, a = 13.891(4) Å, b = 18.188(7) Å, c = 15.012(4) Å, β = 92.70(2)°, space group C2/c, Z = 4; 4 ·MeOH·1.42 i Pr 2 O, C 67.52 H 96.88 Cl 3 N 12 Ni 3 O 6.42, monoclinic, a = 12.400(2) Å, b = 13.520(1) Å, c = 24.616(3) Å, β = 102.04(1)°, space group Pn, Z = 2; 5 ·2Me 2 CO, C 63 H 83 N 12 BF 4 Ni 3 O 7, monoclinic, a = 14.521(3) Å, b = 18.827(3) Å, c = 26.283(4) Å, β = 105.85(2)°, space group: P 2 1 / c, Z = 4. The effects on the type of complex formed with varying steric hindrance on the pyrazole rings is discussed.