Substituted deuteroporphyrins.  V.  Structures, stabilities, and properties of nickel(II) complexes with axial ligands

McLees, Byron D.; Caughey, Winslow S.

doi:10.1021/bi00842a020

Cited by 98 publications

(42 citation statements)

References 26 publications

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“…This effect was first seen for Ni II , as described by Herges et al It is general knowledge that the spin state of nickel(II) complexes depends on the coordination number and geometry. In square‐planar complexes, Ni II shows diamagnetic behavior, with S = 0, but if the geometry changes to tetrahedral,, or the coordination number increases to five or six, the spin state changes to S = 1, resulting in a paramagnetic complex . If the coordination of the axial ligand(s) is triggered by light, the effect is more specifically termed light‐driven coordination‐induced spin‐state switching (LD‐CISSS).…”

Section: Introductionmentioning

confidence: 99%

“…shows diamagnetic behavior, with S = 0, but if the geometry changes to tetrahedral, [22,23] or the coordination number increases to five or six, the spin state changes to S = 1, resulting in a paramagnetic complex. [24][25][26][27][28][29][30][31] If the coordination of the axial ligand(s) is triggered by light, the effect is more specifically termed light-driven coordination-induced spin-state switching (LD-CISSS). Two variants of the LD-CISSS effect have been described in the literature (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Coordination‐Induced Spin‐State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions

et al. 2018

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Four nickel(II) salpn (salicylidenepropylene iminate) complexes are investigated concerning their capability to perform CISSS (coordination‐induced spin‐state switching). To this end, pyridine titration experiments are performed with the nickel salpn complexes [Ni(salpn)], [Ni(salpntBuCF3)], [Ni(salpnCF3)] and [Ni(salpnSbenz)]. The electronic‐structural changes are monitored by UV/Vis spectroscopy and Evans NMR spectroscopy. Association constants (K1s and K2), as well as thermodynamic parameters (ΔH, ΔS, and ΔG), for the binding of pyridine are determined. In comparison with porphyrins and porphyrin‐derived systems investigated earlier, the salpn systems exhibit quite different coordination properties. In particular, the fluorinated systems show the formation of dimers due to CH–π and π–π stacking. On the other hand, the investigated compounds coordinate axial ligands with affinities comparable with those of the porphyrin‐based analogs. This renders them eligible for the preparation of LD‐CISSS (light‐driven CISSS) systems, which, in turn, may be applied as functional MRI contrast agents.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coordination‐Induced Spin‐State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions

et al. 2018

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“…spintronics, data storage, 3,4 switchable diamagnetic levitation 5 or responsive ("smart") contrast agents for magnetic resonance imaging (MRI). [15][16][17][18][19][20][21] We have demonstrated highly efficient and fatigue resistant light-driven coordinationinduced spin state switching (LD-CISSS) by adding photodissociable ligands [22][23][24] to a solution of a Ni 2+ -porphyrin (PDL approach) as well as by tethering azopyridines directly to the porphyrin ("record player" approach). [11][12][13][14] Ni 2+ complexes change their spin state from diamagnetic (S = 0) to paramagnetic (S = 1) when the coordination sphere is changed from square planar (CN = 4) to square pyramidal (CN = 5) or square bipyramidal (CN = 6).…”

Section: Introductionmentioning

confidence: 99%

Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents

et al. 2016

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Azo-N-methylimidazole functionalized Ni(ii)porphyrins were rationally designed and synthesized and their performance as molecular spin switches was investigated. They perform intramolecular light-driven coordination-induced spin state switching (LD-CISSS) in the presence of water and therefore are an important step towards spin switches for medicinal applications, particularly functional MRI contrast agents.

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“…donor-acceptor systems · nickel · porphyrinoids · pyridine · spin crossover drawing substituents at the meso position of the porphyrin (substituents R in Scheme 1) favor the association of axial ligands. [4] Walker et al observed a Hammett relationship of b (K 1S K 2 ) of piperidine with various porphyrins as a function of the meso substituent (R = p-C 6 H 4 R'). [5] A closer look reveals that the increase of the association constant induced by the electron deficiency of the porphyrin and the donor strength of the axial ligand is more pronounced for K 1S than for K 2 .…”

Section: Introductionmentioning

confidence: 99%

Coordination‐Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel–Porphyrins: σ‐Donor versus π‐Acceptor Effects

Thies

Bornholdt

Köhler

et al. 2010

Chemistry A European J

116

158

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Nickel-porphyrins, with their rigid quadratic planar coordination framework, provide an excellent model to study the coordination-induced spin crossover (CISCO) effect because bonding of one or two axial ligands to the metal center leads to a spin transition from S=0 to S=1. Herein, both equilibrium constants K(1S) and K(2), and for the first time also the corresponding thermodynamic parameters DeltaH(1S), DeltaH(2), DeltaS(1S), and DeltaS(2), are determined for the reaction of a nickel-porphyrin (Ni-tetrakis(pentafluorophenyl)porphyrin) with different 4-substituted pyridines by temperature-dependent NMR spectroscopy. The association constants K(1S) and K(2) are correlated with the basicity of the 4-substituted pyridines (R: OMe>H>CO(2)Et>NO(2)) whereas the DeltaH(1S) values exhibit a completely different order (OMeCO(2)Et>NO(2)). 4-Nitropyridine exhibits the largest binding enthalpy, which, however, is overcompensated by a large negative binding entropy. We attribute the large association enthalpy of nitropyridine with porphyrin to the back donation of electrons from the Ni d(xz) and d(yz) orbitals into the pi orbitals of pyridine, and the negative association entropy to a decrease in vibrational and internal rotation entropy of the more rigid porphyrin-pyridine complex. Back donation for the nitro- and cyanopyridine complexes is also confirmed by IR spectroscopy, and shows a shift of the N-O and C-N vibrations, respectively, to lower wave numbers. X-ray structures of 2:1 complexes with nitro-, cyano-, and dimethylaminopyridine provide further indication of a back donation. A further trend has been observed: the more basic the pyridine the larger is K(1S) relative to K(2). For nitropyridine K(2) is 17 times larger than K(1S) and in the case of methoxypyridine K(2) and K(1S) are almost equal.

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Substituted deuteroporphyrins. V. Structures, stabilities, and properties of nickel(II) complexes with axial ligands

Cited by 98 publications

References 26 publications

Coordination‐Induced Spin‐State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions

Coordination‐Induced Spin‐State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions

Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents

Coordination‐Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel–Porphyrins: σ‐Donor versus π‐Acceptor Effects

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