A new family of 1D, 2D and 3D frameworks aggregated from Ni5, Ni4 and Ni7 building units: synthesis, structure, and magnetism

Abstract

Three new Ni(II)-clusters based on a Y-shaped ligand (biphenyl-3,4′,5-tricarboxylate, H₃BPT), [Ni₅(HBPT)₄(OH)₂(H₂O)₁₂]_n (1), [Ni₄(BPT)₂(OH)₂(H₂O)₆]_n·4nH₂O (2), and [Ni₇(BPT)₂(1,4-bib)₂(OH)₆(HCO₂)₂]_n·3nH₂O (3) (1,4-bib = 1,4-bi(1H-imidazol-1-yl)benzene), have been synthesized under solvothermal conditions. They were studied by infrared spectroscopy (IR), single crystal X-ray diffraction, thermogravimetric analysis (TGA), and magnetochemistry. The complexes contain low nuclear Ni-clusters as building units (BUs). Structurally, in 1, the cluster BUs of [Ni₅(μ₃-OH)₂]⁸⁺ can be viewed as two reverse triangles sharing a common vertex, which are connected by the partially deprotonated μ₂–η¹:η¹-HBPT²⁻ forming 1D chains. The BUs of [Ni₄(μ₃-OH)₂]⁶⁺ clusters in 2 can be considered as two reverse triangles sharing a common edge and extended by deprotonated μ₆–η¹:η¹:η¹:η¹:η²-BPT³⁻ constructing a 2D framework. The 3D framework of complex 3 consists of a [Ni₇(μ₃-OH)₄(R-COO)₇(HCO₂)₃] cluster BUs with fully deprotonated μ₅–η¹:η¹:η¹:η¹:η¹:η¹-BPT³⁻ and 1,4-bib ligands. In addition, TGA reveals that the complexes are stable in the range of 293–548 K. Magnetostructural analyses indicate ferromagnetic coupling of J₁ = 1.85(3) and J₂ = 2.25(4) cm⁻¹ in 1 and J = 5.76(6) cm⁻¹ in 2, whereas magnetic parameters J₁ = −2.64(3), J₂ = −23.22(19) and J₃ = 12.02(5) cm⁻¹ indicate an alternating magnetic chain (AF/F) in 3.