Structure and magnetic properties of a novel heteroheptanuclear metal string complex [Ni 3 Ru 2 Ni 2 (μ 7 -teptra) 4 (NCS) 2 ](PF 6 ).

We report the synthesis of a novel heteroheptanuclear metal string complex (HMSC) [Ni3Ru2Ni2(mu(7)-teptra)(4)(NCS)(2)](PF6) 1 supported by tetra-pyridyl-tri-amine (H(3)teptra) ligands. We employed X-ray diffraction and other spectroscopic techniques to characterize the complex. The observed remarkably short Ru-Ru distance of 2.2499(3) angstrom for 1 is indicative of a unique metal-metal interaction in the mixed-valence [Ru-2](5+) (S = 3/2) unit. The complex exhibits a relatively high magnetic moment value of 4.55 B.M. at 4 K, which increases rapidly to 6.00 B.M. at 30 K and remains at 6.11 B.M. from 50 to 300 K as shown by SQUID measurements, indicating a high spin (S >= 3/2) system which is further supported by the analyses of EPR spectra at low temperatures. These magnetic behaviors can be ascribed to the result of spin-exchange interactions among multi-spin centers.