Spin Crossover Induced by Changing the Identity of the Secondary Metal Ion from PdII to NiII in a Face-Centered FeII8MII6 Cubic Cage (original) (raw)
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2022
The assembly of multifunctional polynuclear coordination cages exhibiting spin-crossover (SCO) proves to be a challenge to researchers. Previous investigations into the magnetic properties of a large cubic metallosupramolecular cage, [Fe8Pd6L8] 28+ , constructed using semi-rigid metalloligands and encompassing an internal void of 41 Å 3 , found that the Fe(II) centres that occupied the corners of the cubic structure did not undergo a spin-transition. In this work, substitution of the linker metal on the face of the cage resulted in the onset of spin crossover, as evidenced by magnetic susceptibility, Mӧssbauer and single crystal X-ray diffraction. Structural comparisons of these two cages were undertaken to shed light on the possible mechanism responsible for switching of the [Fe8M(II)6L8] 28+ architecture from SCO inactive to active by simply changing in the identity of M(II). This led to the suggestion that a possible interplay of intra-and intermolecular interactions may permit SCO in the Ni(II) analogue, 1. The distorted octahedral coordination environment of the secondary Ni(II) centres occupying the cage faces provided conformational flexibility for the eight metalloligands of the cubic architecture relative to the square planar Pd(II) environment. Meanwhile the occupation of axial coordination sites of the Ni(II) cations by CH3CN prevented the close packing of cages observed for the Pd(II) analogue, leading to a more offset, distant packing arrangement of cages in the lattice, whereby important areas of the cage that were shown to change most dramatically with SCO experienced a lesser degree of steric hindrance to conformational changes upon SCO. Design through selectivity of secondary metal centres on the flexibility of metalloligand structures and the effect of axial donors 3 packing arrangements may serve as new routes in the engineering of SCO or non-SCO cage systems. The Supporting Information is available free of charge on the ACS Publications website at DOI:. CCDC 2194121-2194125 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk, or by emailing
Angewandte Chemie International Edition
Twon ew heterobimetallic cages,at rigonal-bipyramidal and ac ubic one,w ere assembled from the same mononuclear metalloligand by adopting the molecular library approach,u sing iron(II) and palladium(II) building blocks. The ligand system was designed to readily assemble through subcomponent self-assembly.I ta llowed the introduction of steric strain at the iron(II) centres,w hich stabilizes its paramagnetic high-spin state.This steric strain was utilized to drive dynamic complex-to-complex transformations with both the metalloligand and heterobimetallic cages.A ddition of sterically less crowded subcomponents as ac hemical stimulus transformed all complexes to their previously reported lowspin analogues.The metalloligand and bipyramid incorporated the new building blockm ore readily than the cubic cage, probably because the geometric structure of the sterically crowded metalloligand favours the cube formation. Furthermore it was possible to provokes tructural transformations upon addition of more favourable chelating ligands,converting the cubic structures into bipyramidal ones. Metallosupramolecular chemistry [1] has produced many beautiful structures with defined shapes [2] and fascinating functionality. [3] Within metallosupramolecular chemistry, apowerful tool is the subcomponent self-assembly approach, in which aggregates emerge from the assembly of two ligand
An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin-Crossover Behavior
Angewandte Chemie (International ed. in English), 2017
By employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or its zinc(II) complex, 1H-4-imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O-symmetric cages having a confined volume of ca. 1300 Å(3) . The use of iron(II) salts yielded coordination cages in the high-spin state at room temperature, manifesting spin-crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X-ray crystallography, high-resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state-of-the-art DFT calculations. A remarkably high-spin-stabilizing effect through encapsulation of C70 was observed. The spin-transition temperature T1/2 is lowered by 20 K in the host-guest complex.
A Ferromagnetically Coupled, Bell-Shaped [Ni4Gd5] Cage
Inorganic Chemistry, 2019
Reaction between NiCl2•6H2O, 2-hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime (H2L), benzoic acid and M(NO3)3•6H2O (M = Gd, Y) in MeCN under basic conditions, yields the complexes [Ni II 4Gd III 5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl•13.6MeCN•H2O (1•13.6MeCN 2 •H2O) and [Ni II 4Y III 5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)1.5(H2O)0.5]0.5Cl(NO3)•3H2O (2•3H2O). Both clusters display similar structures, consisting of a bell-shaped {Ni II 4M III 5} unit, in which a linear 'zig-zag' {Ni4} subunit bisects the central {M III 5} 'ring'. Direct (dc) and alternating current (ac) magnetic susceptibility measurements carried out in the 2-300 K temperature range for complexes 1 and 2 revealed ferromagnetic intermolecular interactions, while heat-capacity measurements for the Gd analogue suggest that complex 1 lowers its temperature from T = 9.6 K down to 2.3 K by adiabatically demagnetizing from Bi = 7 T to Bf = 0.
Angewandte Chemie International Edition, 2002
Interest in polynuclear complexes of the 3d metals has been stimulated by the search for new magnetic materials [1, and by demonstration of the occurrence of oligonuclear metal centers in proteins such as urease. Of the relatively small number of reported tetranuclear complexes of S 1 nickel(ii) of known structure, the majority have a hemicubane-or ™butterfly-∫ rather than a squarelike core. [4] Of these molecules, just one is entirely antiferromagnetic, [5] while the remainder entail purely ferromagnetic interactions amongst the nickel(ii) ions. [6±10] Oximes have shown promise as bridging ligands for the preparation of polynuclear complexes. [11, 12] The reaction of 1,4,7-triazaheptane (diethylenetriamine, Dien) with the monooxime of 2,3-butanedione (ModaH) in the presence of Ni II ions, instead of yielding the anticipated Schiff base derivative, gave the tetranuclear Ni II compound 1 (dark brown crystals; C 4 H 8 O 2 1,4-dioxane), containing uncondensed but coordinated ketone and amine groups. Figure 1 a shows the structure of the the cation of 1, while Figure 1 b highlights its Ni II core. [{Ni(Dien)} 2 (m 3 -OH) 2 {Ni 2 (Moda) 4 }](ClO 4 ) 2 ¥ 2 C 4 H 8 O 2 ¥ 2 H 2 O 1
Angewandte Chemie International Edition, 2001
Interest in polynuclear complexes of the 3d metals has been stimulated by the search for new magnetic materials [1, and by demonstration of the occurrence of oligonuclear metal centers in proteins such as urease. Of the relatively small number of reported tetranuclear complexes of S 1 nickel(ii) of known structure, the majority have a hemicubane-or ™butterfly-∫ rather than a squarelike core. [4] Of these molecules, just one is entirely antiferromagnetic, [5] while the remainder entail purely ferromagnetic interactions amongst the nickel(ii) ions. [6±10] Oximes have shown promise as bridging ligands for the preparation of polynuclear complexes. [11, 12] The reaction of 1,4,7-triazaheptane (diethylenetriamine, Dien) with the monooxime of 2,3-butanedione (ModaH) in the presence of Ni II ions, instead of yielding the anticipated Schiff base derivative, gave the tetranuclear Ni II compound 1 (dark brown crystals; C 4 H 8 O 2 1,4-dioxane), containing uncondensed but coordinated ketone and amine groups. Figure 1 a shows the structure of the the cation of 1, while Figure 1 b highlights its Ni II core. [{Ni(Dien)} 2 (m 3 -OH) 2 {Ni 2 (Moda) 4 }](ClO 4 ) 2 ¥ 2 C 4 H 8 O 2 ¥ 2 H 2 O 1
A Mixed-Spin Molecular Square with a Hybrid [2×2]Grid/Metallocyclic Architecture
Angewandte Chemie International Edition, 2011
The design and synthesis of molecular architectures displaying a range of tunable and potentially useful properties has been the subject of widespread attention over the past decade. Both discrete and polymeric metallosupramolecular assemblies have been shown to exhibit intriguing properties, with potential applications including gas separation and adsorption, catalysis, photoactivity, magnetism, [5] electrochemistry, [4a] and host-guest behavior. [4c, 6] Cyanidebridged metal-organic framework materials have attracted intense research interest for their magnetic properties; for example, Prussian Blue is known to be a molecule-based magnet with a Curie temperature (T c ) of 5.6 K, while some heterometallic analogues have been shown to function as high T c magnets with ordering temperatures up to 372 K. Metallocycles and grids represent comparatively simple systems in which the tunability of the molecular structure and ensuing physico-chemical properties can be explored. Although a number of grids and metallocycles displaying interesting magnetic and spin-crossover properties have been developed, [5b, 8] the design and successful construction of these systems, particularly those exhibiting multiple spins at room temperature, still represents a significant challenge. Herein we report the synthesis and characterization, and the magnetic and electronic properties, of a mixed-spin Fe 4 -molecular square with a hybrid grid/metallocyclic architecture.
Inorganic Chemistry, 2018
Small changes in steric bulk at the terminus of bis-iminopyridine ligands can effect large changes in the spin state of self-assembled Fe(II)-iminopyridine cage complexes. If the added bulk is properly matched with ligands that are either sufficiently flexible to allow twisted octahedral geometries at the Fe centers or can assemble with unusual mer configurations at the metals, room temperature high spin Fe(II) cages can be synthesized. These complexes maintain their high spin state in solution at low temperatures and have been characterized by Xray crystallographic and computational methods. The high spin M 2 L 3 meso-helicate and M 4 L 6 cage complexes display longer N− Fe bond distances and larger interligand N−Fe−N bond angles than their diamagnetic counterparts, and these structural changes invert the ligand selectivity in narcissistic self-sorting and accelerate subcomponent exchange rates. The paramagnetic cages can be easily converted to diamagnetic cages by subcomponent exchange under mild conditions, and the intermediates of the exchange process can be visualized in situ by NMR analysis.
Design and Synthesis of Porous Nickel(II) and Cobalt(II) Cages
Inorganic Chemistry, 2018
Coordination assemblies containing transition-metal cations with coordinatively unsaturated sites remain a challenging target in the synthesis of porous molecules. Herein, we report the design, synthesis, and characterization of three porous hybrid inorganic/organic porous molecular assemblies based on cobalt(II) and nickel(II). Precise tuning of ligand functionalization allows for the isolation of molecular species in addition to two-and three-dimensional metal−organic frameworks. The cobaltous and nickelous cage compounds display excellent thermal stabilities in excess of 473 K and Brunauer−Emmett−Teller surface areas on the order of 200 m 2 /g. The precise ligand functionalization utilized here to control phases between discrete molecules and higherdimensional solids can potentially further be tuned to optimize the porosity and solubility in future molecular systems. Carboxylate-based porous cages are essentially identical with carboxylate-based metal −organic frameworks (MOFs) in terms of their underlying coordination chemistry. However, their synthesis, characterization, and gas adsorption properties are rather divergent, and as a result, the former are relatively underdeveloped. Many of the canonical carboxylate-based MOF structures have been synthesized for a wide variety of transition-metal cations, whereas porous cages that are isostructural across a series of metal cations are rare. As an illustrative example, Cu 3 (btc) 2 (HKUST-1) and Cu 24 (bdc) 24 (btc 3− = 1,3,5benzenetricarboxylate; bdc 2− = 1,3-benzenedicarboxylate), a three-dimensional MOF and a discrete coordination cage, 1,2 respectively, were reported within 2 years of each other. The MOF has since been reported for nine transition metals, including every metal in the first row from Cr 2+ to Zn 2+.3-7 For comparison, in terms of first-row metals, the M 24 (bdc) 24 cuboctahedral structure has only been reported for Cr 2+ and Cu 2+. 8-11 In order to tune the *
Journal of the American Chemical Society, 2011
The bis-bidentate bridging ligand L {R,R 0 -bis-[3-(2-pyridyl)pyrazol-1-yl]-1,4-dimethylbenzene}, which contains two chelating pyrazolyl-pyridine units connected to a 1,4-phenylene spacer via flexible methylene units, reacts with transition metal dications to form a range of polyhedral coordination cages based on a 2M:3 L ratio in which a metal ion occupies each vertex of a polyhedron, a bridging ligand lies along every edge, and all metal ions are octahedrally coordinated. Whereas the Ni(II) complex [Ni 8 L 12 ]-(BF 4 ) 12 (SiF 6 ) 2 is an octanuclear cubic cage of a type we have seen before, the Cu(II), Zn(II), and Cd(II) complexes form new structural types. [Cu 6 L 9 ](BF 4 ) 12 is an unusual example of a trigonal prismatic cage, and both Zn(II) and Cd(II) form unprecedented hexadecanuclear cages [M 16 L 24 ]X 32 (X = ClO 4 or BF 4 ) whose core is a skewed tetracapped truncated tetrahedron. Both Cu 6 L 9 and M 16 L 24 cages are based on a cyclic helical M 3 L 3 subunit that can be considered as a triangular "panel", with the cages being constructed by interconnection of these (homochiral) panels with additional bridging ligands in different ways. Whereas [Cu 6 L 9 ](BF 4 ) 12 is stable in solution (by electrospray mass spectrometry, ES-MS) and is rapidly formed by combination of Cu(BF 4 ) 2 and L in the correct proportions in solution, the hexadecanuclear cage [Cd 16 L 24 ](BF 4 ) 32 formed on crystallization slowly rearranges in solution over a period of several weeks to the trigonal prism [Cd 6 L 9 ](BF 4 ) 12 , which was unequivocally identified on the basis of its 1 H NMR spectrum. Similarly, combination of Cd(BF 4 ) 2 and L in a 2:3 ratio generates a mixture whose main component is the trigonal prism [Cd 6 L 9 ](BF 4 ) 12 . Thus the hexanuclear trigonal prism is the thermodynamic product arising from combination of Cd(II) and L in a 2:3 ratio in solution, and arises from both assembly of metal and ligand (minutes) and rearrangement of the Cd 16 cage (weeks); the large cage [Cd 16 L 24 ](BF 4 ) 32 is present as a minor component of a mixture of species in solution but crystallizes preferentially.