Targeted self-assembly and quantum Monte Carlo magnetic study of an alternating nickel(ii) 1D coordination polymer composed of highly preorganized binuclear tectons

Abstract

A pyrazolate-based binucleating ligand HL with pyridyl groups in the chelate arms has been used to synthesize the dinickel(II) complex [LNi₂(N₃)(MeOH)₂](ClO₄)₂ (1) and the corresponding 1D polymeric [LNi₂(μ-N₃)₂]_n(NO₃)_n (2) depending on the amount of NaN₃ added. X-Ray crystallography shows that structural parameters of the {LNi₂(N₃)} units are very similar in both compounds. This is ascribed to π–π stacking between the pyridyl rings that leads to rigidification of the framework and a fixed cis-orientation of the remaining coordination sites, which are filled by MeOH molecules in 1 or by a μ_1,3-bridging azide that connects the subunits in 2. Variable-temperature magnetic measurements reveal strong antiferromagnetic coupling with parameters g = 2.21 and J = −60.7 cm⁻¹ for compound 1. Magnetic data for the extended chain 2 have been analyzed by Quantum Monte Carlo (QMC) simulations to give g = 2.34, J₁ = −55 cm⁻¹, and J₂ = −12 cm⁻¹. The known J value for 1 finally allows unambiguous assignment of J₁ to the intrasubunit coupling within each bimetallic chain constituent. The alternation ratio γ = J₂/J₁ signifies a singlet-dimer ground state of the new 1D polymer 2.