Syntheses, Structure, and Properties of the Metal Complexes with 3-(2-Pyridyl)pyrazole-Based Ligands:  Tuning the Complex Structures by Ligand Modifications

In our efforts to design metal complexes with tailored structures, four 3-(2-pyridyl)pyrazole-based ligands, 8-[3-(2-pyridyl)pyrazolmethyl]quinoline (L), 1,4-bis[3-(2-pyridyl)pyrazolyl]-trans-2-butene (L), 2,3-bis[3-(2-pyridyl)pyrazolmethyl]quinoxaline (L), and 1,3,5-tri[3-(2-pyridyl)pyrazolmethyl]-2,4,6-trimethylbenzene (L), have been synthesized and characterized, and their metal complexes with Cu^II, Ni^II, Co^II, and Cd^II ions have been prepared and structurally characterized by single-crystal X-ray diffraction. Using L¹ to react with CuX₂ (X = Ac^-, NO₃^-, or ClO₄^-) or Cd(ClO₄)₂·6H₂O, yielded four mononuclear complexes, [Cu(L¹)₂(OAc)](OAc)(H₂O)₆ (1) [triclinic, space group P1̄, a = 10.513(11) Å, b = 13.875(14) Å, c = 15.776(16) Å, α = 70.98(2)°, β = 83.57(2)°, γ = 69.665(18)°, Z = 2], [Cu(L¹)₂(NO₃)](NO₃)(H₂O)_5.5 (2) [monoclinic, space group C2/c, a = 12.395(3) Å, b = 26.267(6) Å, c = 26.362(7) Å, β = 92.635(5)°, Z = 8], [Cu(L¹)₂(H₂O)](ClO₄)₂(H₂O)₂ (3) [orthorhombic, space group Pbca, a = 13.326(4) Å, b = 21.715(6) Å, c = 26.318(8) Å, Z = 8], and [Cd(L¹)₃](ClO₄)₂(H₂O)_5/2 (4) [triclinic, space group P1̄, a = 12.485(5) Å, b = 15.142(6) Å, c = 15.190(6) Å, α = 83.104(7)°, β = 75.796(7)°, γ = 79.584(7)°, Z = 2]. The reaction of L² with Cu(ClO₄)₂·6H₂O or Co(NO₃)₂·6H₂O yielded two double helical dinuclear complexes:  [Cu₂(L²)₂(H₂O)₂](ClO₄)₄(H₂O) (5) [triclinic, space group P1̄, a = 10.791(4) Å, b = 13.923(7) Å, c = 19.756(9) Å, α = 72.297(12)°, β = 78.201(14)°, γ = 68.683(13)°, Z = 2] and [Co(L²)(NO₃)(H₂O)]₂(NO₃)₂ (6) [orthorhombic, space group Pbcn, a = 18.170(7) Å, b = 13.240(5) Å, c = 19.064(7) Å, Z = 4]. When L² was replaced by L³ to react with Cu(ClO₄)₂·6H₂O or Ni(BF₄)₂·6H₂O, another mononuclear complex, [Cu(L³)(ClO₄)](ClO₄) (7) [triclinic, space group P1̄, a = 10.1298(6) Å, b = 12.3163(6) Å, c = 12.9485(7) Å, α = 111.533(2)°, β = 106.068(2)°, γ = 99.921(2)°, Z = 2], and a novel tetranuclear complex, [Ni₂(L³)₂(H₂O)₄]₂(SO₄)₂(BF₄)₄(H₂O)₈(CH₃OH)₈ (8) [triclinic, space group P1̄, a = 13.818(8) Å, b = 16.645(8) Å, c = 20.937(11) Å, α = 109.508(10)°, β = 107.144(9)°, γ = 90.923(9)°, Z = 2], were obtained. L⁴ reacts with Cu(ClO₄)₂·6H₂O, to yield a novel trinuclear complex, [Cu₃(L⁴)(H₂O)₉](ClO₄)₅(OH)(CH₃CN)(H₂O)_4.5 (9) [monoclinic, space group C2/c, a = 32.067(12) Å, b = 25.610(9) Å, c = 17.498(7) Å, β = 115.187(6)°, Z = 4]. These results show that the nuclearity of metal complexes may be tuned by ligand modifications, and the nature of ligands, metal ions, counteranions, and solvent molecules play important roles in the formation of such coordination architectures. The emission properties of complexes 7 and 8 have been further studied.