Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

This article presents the syntheses, crystal structures, topological features and magnetic properties of two NiII/NaI coordination clusters formulated [Ni3IINa(L1)3(HL1)(MeOH)2] (1) and [Ni6IINa(L1)5(CO3)(MeO)(MeOH)3(H2O)3]·4(MeOH) 2(H2O) [2 4(MeOH) 2(H2O)] where H2L1 is the semi-rigid Schiff base ligand (E)-2-(2-hydroxy-3-methoxybenzylideneamino)-phenol). Compound 1 possesses a rare Ni3IINaI cubane (3M4-1) topology, and compound 2 is the first example in polynuclear Ni/Na chemistry that exhibits a 2,3,4M7-1 topology.

Having all these in mind, in this article we study the influence of the presence of Na cations and CO3 2anions on the nuclearity of the given chemical system Ni(II)/H2L1 and we report two

Experimental
Materials. Chemicals (reagent grade) were purchased from Sigma Aldrich and Alfa Aesar. All experiments were performed under aerobic conditions using materials and solvents as received.
and H-atoms were introduced at calculated positions and allowed to ride on their carrier atoms.
For 1, attempts to model the lattice solvents (2MeOH) were unsuccessful despite multiple data collections. Therefore, the solvent mask function of Olex2 [80] was employed to remove the contribution of the electron density associated with those molecules from the intensity data.
Geometric/crystallographic calculations for all structures were performed using PLATON, [85] Olex2, [80] and WINGX [82] packages; graphics were prepared with Crystal Maker. [86] CCDC 1476870-1476871 Magnetic studies. Magnetic susceptibility measurements were carried out on polycrystalline samples with a MPMS5 Quantum Design susceptometer working in the range 30-300 K under external magnetic field of 0.3 T and under a field of 0.03T in the 30 -2 K range to avoid saturation effects.
Diamagnetic corrections were estimated from Pascal Tables. The quality of the fitting is parametrized as the factor R = (MTexp-MTcalc) 2 /(Mexp) 2 .

Synthesis of [2 4(MeOH) 2(H2O)]
A similar synthetic procedure to 1 was followed, however after filtration the solution was placed in a vial which in turn was placed in a larger vial that contained a saturated aqueous solution of Na2CO3.
A few drops of conc HCl was added to the saturated to solution and the vial was immediately sealed.

Results and Discussion
Two Ni II /Na II CCs were synthesised. The aim to use of Na2CO3 as the base to introduce carbonate bridges to the system results in the presence of one Na I in both CCs, while both compounds have different structures to the previously reported homometallic Ni II CC with H2L1. [69] In 1, the use of Na2CO3 did not result in the introduction of carbonate bridging groups, however in 2 where the reaction solution was exposed to a high CO2 atmosphere during slow evaporation, a single CO3 2anion is observed. 1 and 2 are new additions to a large family of previously reported Ni II /Na I CCs. According to a nomenclature, developed by some of us, [92] the decorated core of this compound is assigned 3M4-1 (Figure 1).     Adopting our topological approach, the core of compound 2 can be enumerated as 2,3,4M7-

1.[92]
The 2,3,4M7-1 core topology can be viewed as two lozenges fused with a shared apex vertices (Figure β lower), this can be otherwise described as a "butterfly" motif, where the shared vertices are the body and the protruding lozenges the "wings". The first reported compound of this topology was a mixed valence Mn II /Mn III complex in 1991. [95]. This was subsequently followed by a number of homometallic CCs, including Mn III , [96] and Pb II , [97]. which provides a similar co-ordination environment, with further bridging attributed to the third hydroxyl group in H3L5. To the best of our knowledge 2 is the first example of an Ni II /Na I CC exhibiting the 2,3,4M7-1 topology. Moreover, ignoring the existence of the Na ion, then the motif of the hexanuclear Ni6 unit can be enumerated as 1,2,2,3,3M6-1 ( Figure S3), which has been reported only once before in Zinc chemistry. [99] (6) The χMT value at room temperature for compound 1 is 3.97 cm 3 Kmol -1 , increase on cooling to a maximum value of 4.50 cm 3 Kmol -1 at 13 K, prior to decrease at low temperature, indicating a dominant weak ferromagnetic interaction. Fit of the experimental data was performed with PHI [100] program and applying the Hamiltonian: H = -2J1(S1·S2 + S1·S3) -2J2(S2·S3) including a Dion parameter. Considering the Dion parameter an excellent fit of the experimental data was obtained for the parameters J1 = 3.6 cm -1 , J2 = -2.3 cm -1 , D = 1.2 cm -1 , g = 2.26 and R = 4.2·10 -5 but this was not the case when the isotropic Hamiltonian were applied. The shape of the χMT plot corresponds to a weak ferromagnetic coupling with a strong decrease at low temperature due to combination of the AF component and the ZFS of the same order of magnitude than J.
The χMT value at room temperature for 2 is 7.