Synthesis, Crystal Structures, and Magnetic Properties of a Series of Linear Pentanickel(II) Complexes:  [Ni₅(μ₅-tpda)₄X₂] (X = Cl^-, CN^-, N₃^-, NCS^-) and [Ni₅(μ₅-tpda)₄(CH₃CN)₂]- (PF₆)₂ (tpda^2- = the Tripyridyldiamido Dianion)

Abstract

The synthesis, crystal structures, and magnetic properties of linear pentanuclear complexes, [Ni(5)(&mgr;(5)-tpda)(4)X(2)](n)()(+) [tpdaH(2) = tripyridyldiamine, with different axial ligands X = Cl(-) (1), CN(-) (2), N(3)(-) (3), and NCS(-) (4) (n = 0) and CH(3)CN (5) (n = 2)], are reported. All of the [Ni(5)(tpda)(4)](2+) moieties are isostructral and involve a Ni(5) linear chain unit with all of the angleNi-Ni-Ni being nearly 180 degrees, terminated by the two axial ligands. The pentanuclear linear metal chain is helically wrapped by four syn-syn-syn-syn type tpda(2-) ligands. There are two types of Ni-Ni distances existing in these complexes. The terminal Ni-Ni distances bonded with the axial ligand are longer (2.35-2.40 Å) and affected by various axial ligands. The inner Ni-Ni distances are very short and remain constant ( approximately 2.30 Å). The relationship between terminal Ni-Ni distances and properties of the axial ligands on 1-5 will be discussed. Two terminal Ni(II) ions bonded with the axial ligands are in a square-pyramidal (NiN(4)X) environment and exhibit long Ni-N bonds ( approximately 2.10 Å) which are consistent with a high-spin Ni(II) configuration. The inner three Ni(II) ions display short Ni-N ( approximately 1.90 Å) bond distances which are consistent with a square-planar (NiN(4)), diamagnetic arrangement of a low-spin Ni(II) configuration. All compounds exhibit similar magnetic behavior, indicating an antiferromagnetic interaction of two terminal high-spin Ni(II) ions in these complexes. The XANES (X-ray absorption near-edge absorption spectroscopy) spectra also confirm the existence of the high-spin and low-spin Ni(II) ions in these complexes.

From Homonuclear Metal String Complexes to Heteronuclear Metal String Complexes

“…To synthesize longer linear oligonuclear metal complexes, a rational method is to extend the length of the dpa ligand through the palladium-catalyzed cross-coupling reaction of aminoand chloropyridines. By using these longer oligopyridylamido ligands, several pentanuclear [M 5 (tpda) 4 Cl 2 ] complexes [M = Ni II (7), Co II (8), Cr II (9), and Ru II (10); tpda 2-= tripyridyldiamido], [11] heptanuclear [M 7 (teptra) 4 Cl 2 ] complexes [M = Ni II (11) and Cr II (12), teptra 3-= tetrapyridyltriamido], [12] and nonanuclear [M 9 (peptea) 4 Cl 2 ] complexes [M = Ni II (13), peptea 4-= pentapyridyltetraamido] [13] have been prepared and characterized.…”

Synthesis, characterization, crystal structure and biological activity of a novel heterotetranuclear complex: [NiLPb(SCN)(DMF)(HO)], bis-{[μ-,′-bis(salicylidene)-1,3-propanediaminato-aqua-nickel(II)](thiocyanato)(μ-thiocyanato)(μ-,′-dimethylformamide)lead(II)}

“…It is well known that Schiff base and its complexes have also antimicrobial and antifungal activity [3,4]. However, polynuclear transition metal complexes supported by pseudohalide bridges have also been studied for their magneto-structural properties [5][6][7][8].…”

“…Both possibilities have been structurally characterized for transition metal complexes [5][6][7][8][9][10][11][12].…”

Optimized ultra-narrow atomic bandpass filters via magneto-optic rotation in an unconstrained geometry

“…Atomic filters can be realized with ground-or excited-state transitions [21][22][23][24][25][26][27][28] or can take advantage of pump-probe techniques, in combination with the Faraday effect to create extremely narrow filters [29], though at the cost of maximum transmission.…”