Density functional theory at the BP86 level was used to investigate the influence of equatorial ligands on the Ni–Ni interactions and magnetic coupling properties of metal string complexes [Ni_3(L)_4(NCS)_2](L represents the rigid equatorial ligands; L = dzp-(1), mpmpa-(2), mppda-(3), mptpa-(4)). The following conclusions can be drawn.(1) With increasing the radius of the connecting atom in the cental ring in equatorial ligands, the two pyridine rings bend down, resulting in the decreasing distance between the two pyridine-nitrogen atoms and the Ni–Ni distance. Therefore, the strength order of the Ni–Ni interaction is 4 > 2 > 3 > 1. The Ni–Ni interactions in 2 and 4 are stronger than those in Ni_3(dpa)_4(NCS)_2 containing no-rigid equatorial ligands.(2) The calculated-Jab is 4 > 2 > 3 > 1. There are two types of magnetic exchange pathways in these complexes: the σ-type pathway through the Ni_3~(6+) chains and the δ-type pathway through the equatorial ligands. The magnetic coupling through the metals is the dominant part. Hence, the magnetic coupling strength increases with increasing the Ni–Ni interaction. Modifying the radius of the connecting atom may be one of the means to fine tuning of magnetic coupling strength of this kind of metal string complexes. Density functional theory at the BP86 level was used to investigate the influence of equatorial ligands on the Ni-Ni interactions and magnetic coupling properties of metal string complexes [Ni_3 (L) _4 (NCS) _2] (L represents the rigid equatorial ligands; L = dzp- (1), mpmpa- (2), mppda- (3), mptpa- (4)). With the radius of the connecting atom in the cental ring in equatorial ligands, the two pyridine rings bend down, resulting in the decreasing distance between the two pyridine-nitrogen atoms and the Ni-Ni distance. Thus, the strength order of the Ni-Ni interaction is 4> 2> 3> 1. The Ni -Ni interactions in 2 and 4 are stronger than those in Ni_3 (dpa) _4 (NCS) _2 containing no-rigid equatorial ligands. (2) The calculated-Jab is 4> 2> 3> 1. There are two types of magnetic exchange pathways in these complexes: the σ-type pathway through the Ni_3 ~ (6+) chains and the δ-type pathway through the equatorial ligands. pling through the metals is the dominant part. Therefore, the magnetic coupling strength increases with increasing the Ni-Ni interaction. Modifying the radius of the connecting atom may be one of the means to fine tuning of magnetic coupling strength of this kind of metal string complexes.