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

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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 μ1,3-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.

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