Crystal and molecular structure of di-.mu.-azido-bis(2,2',2''-triaminotriethylamine)dinickel(II) tetraphenylborate. Magnetic exchange between azide-bridged octahedral nickel(II) centers. Di-.mu.-azido and mono-.mu.-azido cases

Synthesis, characterization, structure and magnetic properties of azido-bridged nickel(II) and copper(II) complexes with a pyridylpyrazole-based ligand

“…Each nickel atom is six coordinated with distorted octahedral environment and is bonded to four nitrogen atoms-pyridine nitrogen (N6), tertiary amine nitrogen (N3) and the two nitrogen atoms (N7 and 120.1(3)°.The NiÁÁÁNi distance is 5.060 Å . This is consistent with the structural results obtained for other end-to-end azido bridging complexes [41]. The molecular structure of the dimeric cationic moiety of complex (2) and the atom-labeling scheme are shown in Fig.…”

Dinuclear Nickel Complexes Doubly Bridged by Hydrogencyanamido Ligands: Synthesis, Structures and Magnetic Properties

“…In each case, χ value increases as temperature decreases and reaches a maximum at around 25 to 50 K. Based on Van Vleck equation for a dimer model with S = 1, spin exchange coupling constants J for complexes 2 – 5 were calculated to be –17.4, –9.7, –5.6 and –13.2 cm –1 , respectively, revealing that these complexes are antiferromagnetic . The absolute values of these coupling constants are smaller than those of dinuclear nickel complexes bridged by two µ 2 ‐N 3 ‐ N , N′ ligands {for instance, J = –35.1 cm –1 for [Ni 2 (tren) 2 (µ 3 ‐N 3 ‐ N , N′ )] 2+ },[5a] suggesting that spin–spin interaction in a dimeric complex bridged by hydrogencyanamido ligand is weaker than that in the corresponding azido complex. The | J| values have correlation with the bent angles of the central eight‐membered rings defined in Table : smaller bent angles cause larger | J| values (Figure S4).…”

“…As already pointed out, these complexes possess unsymmetric NCNH bridges reflecting the monoprotonated nature, while the azido‐bridged complexes often have more symmetric N 3 bridges with similar two N–N distances and Ni–N–N angles. [5a], [5b], However, the conformations of the eight‐membered (NiNCN) 2 rings in 2 – 5 resemble those found in azido‐bridged complexes;, they adopt a flat chair‐like conformation, where the deviation from planarity of the core depends on the ancillary ligands (Figure S4). In complexes 2 and 5 , the Ni 2 N 4 C 2 skeletons are almost planar, while those in 3 and 4 are more folded with the bent angles (NiN 2 /N 4 C 2 ) of 15.98 and 24.75°, respectively.…”

“…Similar absorption bands in the visible and NIR region are also found in the case of related azido‐bridged complexes. [5c] For complexes 1 and 2 , a strong absorption probably due to the π–π* transition reaches to ca. 480 nm, while for 3 and 4 , almost no absorption is detected in the same region and instead, a weak absorption is observed at 360 nm.…”

“…Especially, azide (N 3 – ) is a well‐investigated bridging ligand composed of three nitrogen atoms, and various types of multinuclear azido complexes have been synthesized . It has been revealed that the coordination mode of azido ligands affects magnetic properties of the complexes: ferromagnetic coupling is commonly found in complexes adopting an end‐on (µ 2 ‐ N , N ) bridging mode, while complexes with an end‐to‐end (µ 2 ‐ N , N′ ) bridging mode usually have antiferromagnetic character (Figure a) …”