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

A pyrazolate-based binucleating ligand HL with pyridyl groups in the chelate arms has been used to synthesize the dinickel(II) complex [LNi2(N-3)(MeOH)(2)](ClO4)(2) (1) and the corresponding 1D polymeric [LNi2(mu-N-3)(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 pi-pi 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 mu(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, J(1) = -55 cm(-1), and J(2) = -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 gamma = J(2)/J(1) signifies a singlet-dimer ground state of the new 1D polymer 2.