Self-assembling iron(II), 2-fluoropyrazine (Fpz), and [M(CN)] (M = Ni, Pd, Pt) or [Au(CN)] building blocks have afforded a new series of two- (2D) and three-dimensional (3D) Hofmann-like spin crossover (SCO) coordination polymers with strong cooperative magnetic, calorimetric, and optical properties. The iron(II) ions, lying on inversion centers, define elongated octahedrons equatorially surrounded by four equivalent centrosymmetric μ-[M(CN)] groups. The axial positions are occupied by two terminal Fpz ligands affording significantly corrugated 2D layers {Fe(Fpz)([M(CN)]}. The Pt and Pd derivatives undergo thermal- and light-induced SCO characterized by T temperatures centered at 155.5 and 116 K and hysteresis loops 22 K wide, while the Ni derivative is high spin at all temperatures, even at pressures of 0.7 GPa. The great stability of the high-spin state in the Ni derivative has tentatively been ascribed to the tight packing of the layers, which contrasts with that of Pt and Pd derivatives in the high- and low-spin states. The synthesis and structure of the 3D frameworks formulated {Fe(Fpz)[Pt(CN)]}·1/2HO and {Fe(Fpz)[Au(CN)]}, where Fpz acts as bridging ligand, which is also discussed. The former is high spin at all temperatures, while the latter displays very strong cooperative SCO centered at 243 K accompanied by a hysteresis loop 42.5 K wide. The crystal structures and SCO properties are compared with those of related complexes derived from pyrazine, 3-fluoropyridine, and pyridine.
Little is known about the mechanisms behind the bistability
(memory)
of molecular spin transition compounds over broad temperature ranges
(>100 K). To address this point, we report on a new discrete Fe
II
neutral complex [Fe
II
L
2
]
0
(
1
) based on a novel asymmetric tridentate ligand 2-(5-(3-methoxy-4
H
-1,2,4-triazol-3-yl)-6-(1
H
-pyrazol-1-yl))pyridine
(L). Due to the asymmetric cone-shaped form, in the lattice, the formed
complex molecules stack into a one-dimensional (1D) supramolecular
chain. In the case of the rectangular supramolecular arrangement of
chains in methanolates
1-A
and
1-B
(both
orthorhombic,
Pbcn
) differing, respectively, by bent
and extended spatial conformations of the 3-methoxy groups (3MeO),
a moderate cooperativity is observed. In contrast, the hexagonal-like
arrangement of supramolecular chains in polymorph
1-C
(monoclinic,
P
2
1
/
c
) results in steric coupling of the transforming complex
species with the peripheral flipping 3MeO group. The group acts as
a supramolecular latch, locking the huge geometric distortion of complex
1
and in turn the trigonal distortion of the central Fe
II
ion in the high-spin state, thereby keeping it from the
transition to the low-spin state over a large thermal range. Analysis
of the crystal packing of
1-C
reveals significantly changing
patterns of close intermolecular interactions on going between the
phases substantiated by the energy framework analysis. The detected
supramolecular mechanism leads to a record-setting robust 105 K wide
hysteresis spanning the room temperature region and an atypically
large
T
LIESST
relaxation value of 104
K of the photoexcited high-spin state. This work highlights a viable
pathway toward a new generation of cleverly designed molecular memory
materials.
The influence of the charge and steric hindrance on the spin state of a series of four monomeric Fe(II) complexes derived from the tridentate ligands 2-(1H-benzoimidazol-2-yl)-1,10-phenanthroline (Hphenbi) and 2-(1H-benzoimidazol-2-yl)-9-methyl-1,10-phenanthroline (Hmphenbi) and their deprotonated forms (phenbi(-), mphenbi(-)) are investigated. The crystal structure and magnetic properties show that [Fe(Hphenbi)2](BF4)2·1.5C6H5NO2·H2O (1) and its neutral form [Fe(phenbi)2](0)·2CHCl3·H2O (2) are low-spin complexes at 400 K due to the strong ligand field imparted by the terpyridine-like ligand. In contrast, the steric hindrance induced by the methyl group in [Fe(Hmphenbi)2](BF4)2 (3) stabilizes the high-spin state of the Fe(II) ion at all temperatures. Application of a hydrostatic pressure of 0.43 GPa shows that3 displays incomplete thermal-induced spin crossover behaviour. However, upon deprotonation of the ligand the resulting neutral complex [Fe(mphenbi)2]·2CHCl3 (4) shows a complete two-step spin crossover behaviour at ambient pressure.
The reaction of Salen-like Zn II and Ni II precursors with carbacylamidophosphate lanthanide moieties yields six new types of 3d-4f compounds. The complexes were characterized by means of 1 H, 31 P NMR and IR spectroscopy, elemental analysis, ESI mass spectrometry, and X-ray diffraction analysis. Depending on the Schiff base ligands, the Ni II ion adopts either a square-planar or an octahedral geometry,[a] 3720 whereas the Zn II ion has a tetragonal-pyramidal geometry. The coordination number of lanthanides is nine or ten. Hydrolytic activities of some heterobimetallic Zn-Ln and Ni-Ln coordination compounds in the reaction of intramolecular hydrolytic degradation of the 2-(hydroxypropyl)-p-nitrophenyl phosphate were investigated. uclear complexes. [3][4][5][6] However, the investigations in the field of 3d-4f heterobinuclear compounds have mainly focused on their applications in magnetism and luminescence, [7][8][9][10][11][12][13][14][15] whereas their application in areas such as catalysis has, to our knowledge, not been reported.Recently, we have studied heteroleptic coordination compounds with β-diketone derivatives as carbacylamidophosphates (CAPh), containing the functional fragment C(O)-NHP(O). [16,17] Here, we report the synthesis, structural characterization, and catalytic properties of new binuclear 3d-4f complexes based on unsaturated lanthanide moieties with CAPh, and complexes of Zn II and Ni II with Schiff bases as additional ligands (Scheme 1). Scheme 1. Precursors for syntheses of 3d-4f complexes.
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