Tetranuclear Nickel Complexes Composed of Pairs of Dinuclear LNi₂ Fragments Linked by 4,4′‐Bipyrazolyl, 1,4‐Bis(4′‐pyrazolyl)benzene, and 4,4′‐Bipyridazine: Synthesis, Structures, and Magnetic Properties

Abstract

The ability of the ligands 4,4′‐bipyrazolyl (H2bpz), 1,4‐bis(4′‐pyrazolyl)benzene (H2bpzb), and 4,4′‐bipyridazine (bpdz) to link two dioctahedral LNi2 units has been examined. Thefollowing complexes were prepared: [L1NiII2(Hbpz)][BPh4] (6[BPh4]), [L1NiII2(bpdz)][ClO4]2 (7[ClO4]2), [(L1NiII2)2(bpzb)][BPh4]2 (8[BPh4]2), and [(L2NiII2)2(bpz)][BPh4]2 (9[BPh4]2), where (L1)2– and (L2)2– represent macrocyclic hexaaza‐dithiophenolate ligands. All complexes have been characterised by UV/Vis spectroscopy, IR spectroscopy, and X‐ray crystallography. Whereas (Hbpz)– and bpdz in 6[BPh4]2 and 7[ClO4]2 act as bidentate ligands coordinating to only one [LNi2]2+ unit, in 8[BPh4]2 and 9[BPh4]2 the (bpzb)2– and(bpz)2– units are tetradentate linkers. This is qualitatively explained in terms of the absence or presence of steric repulsions between the tBu groups of the supporting ligands and the length of the coligands. The structures of the tetranuclear complexes differ mainly in the distance between the center of the Ni···Ni axes of the isostructural [LNi2] units {14.040(1) Å in 8[BPh4]2, 9.184(1) Å in 9[BPh4]2}. The two Ni2pyrazolato planes in 9[BPh4]2 are coplanar. An analysis of the temperature‐dependent magnetic susceptibility data for 9[BPh4]2 reveals the presence of weak ferromagnetic exchange interactions between the NiII ions in the binuclear [L2Ni2] subunits with values for the magnetic exchange constant J1 of 23.97 cm–1 (H = –2JS1S2). The exchange coupling across the dipyrazolato bridge is less than 0.1 cm–1, suggesting that no significant interdimer exchange coupling occurs in 9[BPh4]2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Tetranuclear Nickel(II) Complexes Composed of Pairs of Dinuclear LNi2 Fragments Linked by Acetylenedicarboxylate, Terephthalate, and Isophthalate Dianions: Synthesis, Structures and Magnetic Properties

“…There seems to be no dependence of the interdimer coupling on the mutual orientation of the Ni 2 O 2 planes, which is in line with our previous observations. [50] …”

Magnetic Properties of Mixed Ligand NiII2 and NiII4 Complexes Composed of Macrocyclic Hexaamine‐Dithiophenolato and Bridging Tetrazolato Ligands

“…<< Figure 4 here >> [4,15], where also no significant interdimer exchange coupling occurs. In conclusion it can be said that weak ferromagnetic exchange interaction can be noted within the dinuclear subunits, but virtually no interaction across the bistetrazolato bridge is seen.…”

Synthesis of 3- and 5-formyl-4-phenyl-1H-pyrazoles: promising head units for the generation of asymmetric imineligands and mixed metal polynuclear complexes

“…4-Phenyl-1H-pyrazole (17, Scheme 5) was therefore prepared, using a protocol reported for the synthesis of 1,4-bis(pyrazol-4 0 -yl)benzene. 24 Under Vilsmeier reaction conditions phenylacetic acid is converted to the intermediate 15 (Scheme 5), which precipitates as a light yellow crystalline material from the 1 : 3 DMF-H 2 O solvent mixture when a saturated aqueous solution of NaBF 4 is added. Basic hydrolysis of 15 produces the unstable intermediate 16 (Scheme 5) which is, in a one pot reaction, acidified to pH 5 and condensed with hydrazine hydrate, to give the desired compound 17 in moderate yield.…”