To further support the sign and magnitude of the experimentally determined magnetic exchange interactions above, DFT calculations have been performed on a [Ni5Zn2] model created from the XRD structure of complex 1 (Figure , Table ). Considering symmetry and structural parameters, complex 1 has a total of five unique magnetic exchange interactions (J1-J4, J1' Figure ). The exchange between the central and ring Ni II ions (Jcr = J1, J1', J3) is calculated to be ferromagnetic and in the range +3.1 cm -1 ≤ Jcr ≤ +5.1 cm -1 . The exchange between neighbouring ring Ni II ions (Jrr = J2, J4) is calculated to be antiferromagnetic and in the range -1.6 cm -1 ≤ Jrr ≤ -6.0 cm -1 . Thus, the signs and magnitudes of the DFT calculated values are in good agreement with the experimentally fitted values derived from the magnetic susceptibility and magnetisation measurements. They are also in agreement with previous magnetostructural studies performed on polymetallic Ni II complexes in which larger average Ni-O-Ni angles result in an antiferromagnetic interaction and smaller average Ni-O-Ni angles result in a ferromagnetic interaction, with the crossover angle being ~97-98 o . Further DFT calculations on dimetallic models (Figures ) also confirm the ferromagnetic Jcr interaction (J1A = +8.2 cm -1 ) and antiferromagnetic Jrr interaction (J1B = -3.1 cm -1 ). To rationalise the magnitude and sign of the magnetic interactions, overlap integral calculations 52 have been performed on the dimetallic models using the singly occupied molecular orbitals (SOMOs) of the Ni II ions. Stronger overlap values between SOMOs leads to an antiferromagnetic interaction, whereas orthogonal/weak overlap values contribute to a ferromagnetic interaction. The overlap integral calculations suggest one moderate and three weak interactions for 1A and two moderate and two weak interactions for 1B. This leads to a ferromagnetic interaction for 1A and an antiferromagnetic interaction for 1B (Figures ). Spin density analysis suggests strong mixing and delocalisation onto the coordinating ligand atoms followed by weak spin polarisation. The ring Ni II ions have a spin density between 1.693 -1.698 and the central Ni II ion has a spin density of 1.735 (Figures ). The smaller spin densities on the ring Ni II ions can be attributed to the stronger spin delocalisation from the Ni II ion to the N atom of the bridging ligand (between 0.050 -0.063). As expected, the µ3-O bridging atoms have a larger spin density compared to the µ2-O bridging atoms. A magneto-structural correlation developed for model 1C (Figure ) with respect to the average Ni-O-Ni angle and average Ni-O distance follows the same trends observed for previously published O-bridged polymetallic Ni II complexes, suggesting a strong dependence of the magnetic exchange interaction on the average Ni-O-Ni angle in particular (Figure ). 51 SHAPE analysis (Table ) suggests distorted octahedral geometries for all the Ni II ions present, with the ring Ni II ions [NiO4N2] being more distorted than the central Ni II ion [NiO6] on account of the chelating hmp/pic ligands. For small distortions away from ideal Oh symmetry, as seen here, one would expect either easy axis or easy plane anisotropy with a magnitude of approximately |D| < 10 cm -1 . 52 Single ion anisotropy parameters for the four unique Ni II ions present in 1 have been estimated using ab initio CASSCF/NEVPT2 calculations in the ORCA suite on model complexes 1D-1G (Figure ) derived from the XRD structure of complex 1. Ab initio NEPVT2 calculations suggest easy axis anisotropy for the ring Ni II ions in the range -5.4 cm -1 ≤ D2 ≤ -7.7 cm -1 , and easy plane anisotropy, D1 = +7.3 cm -1 , for the central Ni II ion (Figure , Table ). The Dzz axes for Ni1-3 lie along the shortest Ni-µ3O distance, whereas for Ni4, Dzz is oriented along the longest Ni-µ3O distance (Figure ). The negative and positive signs of D are thus associated with the compressed and elongated character of the octahedron, respectively. The calculated values are in agreement with the experimentally fitted values from the susceptibility and magnetization data, and consistent with values in the literature. The ground state electronic arrangements for the ring and the central Ni II ions are found to be {(dyz) (dxz) 2 (dxy) 2 (dz 2 ) 1 (dx 2 -y 2