The coordination chemistry of -butylcalix[8]arene with transition and lanthanide metal ions.

A survey of the literature and the Cambridge Structural Database reveals thirty nine -butylcalix[8]arene-supported transition (3d, limited to V-Cu) and lanthanide metal complexes ranging in nuclearity from one to eighteen, twenty of which are homometallic and nineteen of which are heterometallic. We provide a review of the coordination chemistry of these complexes, including our own work in the area. We also provide our thoughts and perspectives on the common structural themes observed, identify gaps in knowledge and evaluate how that may inform and direct future synthetic efforts.

Magnetocaloric effect in a high-spin ferromagnetic molecular cluster.

The reaction of MnCl·4HO with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn] cationic cluster and two [MnCl] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [Mn Mn ] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a = 22 spin ground state for the [Mn Mn ] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling.

A Delocalized Mixed-Valence Dinuclear Ytterbium Complex That Displays Intervalence Charge Transfer.

The analysis of intervalence charge transfer (IVCT) in mixed-valence compounds can help understand electron transfer processes that are important in diverse applications such as molecular electronics and artificial photosynthesis. While mixed-valence complexes of the lanthanides are more difficult to access than their transition metal analogues, they have shown IVCT phenomena derived from Robin-Day Class II localized valency or even electronic transitions due to - metal-metal bonding. In contrast, we report here the synthesis, characterization, and computational analysis of a rare, Robin-Day Class III, singly reduced dinuclear Yb complex, which is best viewed as having delocalized oxidation states.

Tracking the conical intersection dynamics for the photoinduced Jahn-Teller switch of a Mn(iii) complex.

Octahedral Mn(iii) ions predominantly exhibit an axially elongated Jahn-Teller (JT) distortion, which is responsible for their large uniaxial magnetic anisotropy. As a result, they are often used in the synthesis of single-molecule magnets (SMMs). Modulation of the JT distortion using femtosecond laser pulses could offer a route to controlling the magnetisation direction, and therefore is promising for the development of data storage devices that work on ultrafast timescales.

Stellated cuboctahedron of Fe.

The solvothermal reaction of FeCl ⋅ 4HO and HTBC[4] in a basic dmf/EtOH solution affords an [Fe ] Keplerate conforming to a stellated cuboctahedron. Magnetic and heat capacity measurements reveal spin frustration effects arising from the high symmetry. A crossover between inverse and direct magnetocaloric effects is observed at ~10 K for applied-field changes lower than 3 T.

Tracking nuclear motion in single-molecule magnets using femtosecond X-ray absorption spectroscopy.

The development of new data storage solutions is crucial for emerging digital technologies. Recently, all-optical magnetic switching has been achieved in dielectrics, proving to be faster than traditional methods. Despite this, single-molecule magnets (SMMs), which are an important class of magnetic materials due to their nanometre size, remain underexplored for ultrafast photomagnetic switching.

Reaction of PhC(X)(COH) (X = OH, NH) with [VO(OR)] (R = Et, Pr): structure, magnetic susceptibility and ROP capability.

Reaction of [VO(OR)] (R = Et, Pr) with 2,2'-diphenylglycine afforded the alkoxide-bridged dimers {[VO(OR)(μ-OR)][PhC(NH)(CO)]}, whereas use of benzilic acid, in the presence of alkali metals, afforded 16-membered metallocycles {V(O)M(OR)[PhC(OH)(CO)]} (M = <1 Na, K). For the ring systems, magnetic susceptibility data is consistent with mixed-valence vanadium with an average oxidation state of 3.5.

-cage catalysis and initiation derived from photo-activating host-guest encapsulation.

Coordination cage catalysis has commonly relied on the endogenous binding of substrates, exploiting the cavity microenvironment and spatial constraints to engender increased reactivity or interesting selectivity. Nonetheless, there are issues with this approach, such as the frequent occurrence of product inhibition or the limited applicability to a wide range of substrates and reactions. Here we describe a strategy in which the cage acts as an exogenous catalyst, wherein reactants, intermediates and products remain unbound throughout the course of the catalytic cycle.

Odd and Even Numbered Ferric Wheels.

The structurally related odd and even numbered wheels [Fe Zn (tea) (teaH) (OMe)Cl ] (1) and [Fe Zn (tea) Cl ] (2) can be synthesized under ambient conditions by reacting Fe and Zn salts with triethanolamine (teaH ), the change in nuclearity being dictated by the solvents employed. An antiferromagnetic exchange between nearest neighbors, J = -10.0 cm for 1 and J = -12.

Equatorial restriction of the photoinduced Jahn-Teller switch in Mn(iii)-cyclam complexes.

Ultrafast transient absorption spectra were recorded for solutions of [Mn(cyclam)(HO)(OTf)][OTf] (cyclam = 1,4,8,11-tetraazacyclotetradecane and OTf = trifluoromethanesulfonate) in water to explore the possibility to restrict the equatorial expansion following photoexcitation of the d ← d electronic transition, often resulting in a switch from axial to equatorial Jahn-Teller distortion in Mn complexes. Strong oscillations were observed in the excited state absorption signal and were attributed to an excited state wavepacket. The structural rigidity of the cyclam ligand causes a complex reaction coordinate with frequencies of 333, 368, 454 and 517 cm, and a significantly shorter compressed-state lifetime compared to other Mn complexes with less restricted equatorial ligands.

A bis-calix[4]arene-supported [CuII16] cage.

Reaction of 2,2'-bis--Bu-calix[4]arene (HL) with Cu(NO)·3HO and -methyldiethanolamine (Me-deaH) in a basic dmf/MeOH mixture affords [CuII16(L)(Me-dea)(μ-NO)(μ-OH)(dmf)(MeOH)(HO)](HL)·16dmf·4HO (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu], in which the four capping metal ions are the Cu ions housed in the calix[4]arene polyphenolic pockets. The [CuII8] square prism is held together "internally" by a combination of hydroxide and nitrate anions, with the -methyldiethanolamine co-ligands forming dimeric [CuII2] units which edge-cap above and below the upper and lower square faces of the prism.

Tetra-, tetradeca- and octadecametallic clusters of Mn.

Reaction of equimolar amounts of MnBr·4HO and HL ((3,5-dimethyl-1-pyrazol-1-yl)methanol) in a basic MeCN solution leads to the formation of [MnII4(L)Br(HO)] (1), whose metallic skeleton is a [MnII4] tetrahedron and cluster core a [MnII4(μ-O)] cubane. Replacing MnBr·4HO with Mn(OCMe)·4HO affords [MnIII2MnII12O(L)(OAc)] (2) which is best described as a series of edge-sharing [Mn] tetrahedra that have self-assembled into a linear array in which each [Mn] pair is 'twisted' with respect to its neighbours in a corkscrew-like manner. Employment of the triangle [MnIII3O(OAc)(py)](ClO) as a reactant instead of a Mn salt results in the formation of [MnIII14MnII4O(L)(HL)(OAc)(HO)] (3) whose core is comprised of three vertex-sharing [MnIII4] butterflies flanked on either side by one [MnIII4] cubane and one [MnIII2MnII2] tetrahedron.

A {GdNa} Molecular Quadruple-Wheel with a Record Magnetocaloric Effect at Low Magnetic Fields and Temperatures.

Reaction of Gd(OAc)·4HO, salicylaldehyde and CHONa in MeCN/MeOH affords [GdNa(OAc)(HCO)(CO)(HO)]·9HO.0.5MeCN (·9HO.

Controlled Hydrolysis of Phosphate Esters: A Route to Calixarene-Supported Rare-Earth Clusters.

Phosphate ester bonds are widely present in nature (e. g. DNA/RNA) and can be extremely stable against hydrolysis without the help of catalysts.

Against the Norm: Non Irving-Williams Transmetalation in Transition Metal Dimers.

We report the synthesis and characterization of three dinuclear 33' complexes, (), (), and ([CuMn(NO)]), that utilize the ligand, H (6,6'-dimethoxy-2,2'-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol). The relative stabilities of these complexes were investigated using experimental and computational techniques, revealing a non-Irving-Williams transmetalation, whereby a Mn ion can displace a Cu ion from its binding pocket in to yield the more stable complex. Magnetic characterization of the reported complexes revealed an unexpected ferromagnetic coupling between the two Cu ions of with = +63.

A ferromagnetically coupled pseudo-calixarene [Co] wheel that self-assembles as a tubular network of capsules.

Reaction of Co(OAc)·4HO and Hsal in a basic MeCN solution affords the hexadecanuclear wheel [Co(sal)(OAc)]·16MeCN (1·16MeCN) that displays ferromagnetic nearest neighbour exchange and has pseudo-calixarene character. Symmetry equivalent wheels self-assemble to form remarkable tubular networks of capsules in the extended structure.

Constructing "Closed" and "Open" {Mn} Clusters.

Use of the 1,3,5-tri(2-hydroxyethyl)-1,3,5-triazacyclohexane ligand, LH, in manganese chemistry affords access to two structurally related {Mn} clusters: a "closed" {Mn Mn } puckered square wheel of formula [MnL(LH)O(OH)(MeO)Br(imH)(HO)](Br) (; imH = imidazole) and an "open" {Mn } rod of formula [Mn LO(aibH)(aib)(MeO)(MeOH)](NO) (, aibH = 2-amino-isobutyric acid). In each case the triaza ligands, L/LH, direct the formation of {Mn} triangles with their N atoms preferentially bonding to the Jahn-Teller axes of the Mn ions. Subsequent self-assembly is dependent on the anion of the Mn salt and the identity of the organic coligand employed-the terminally bonded imidazole and the chelating/bridging amino acid.

Magneto-thermal properties and slow magnetic relaxation in Mn(II)Ln(III) complexes: influence of magnetic coupling on the magneto-caloric effect.

A family of Mn(II)Ln(III) dinuclear and tetranuclear complexes (Ln = Gd and Dy) has been prepared from the compartmental ligands ,'-dimethyl-,'-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine (HL) and ,',''-trimethyl-,''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (HL). The Mn(II)Gd(III) complexes exhibit antiferromagnetic interactions between Mn(II) and Gd(III) ions in most cases, which are supported by Density Functional Theory (DFT) calculations. Experimental magneto-structural correlations carried out for the reported complexes and other related complexes found in bibliography show that the highest ferromagnetic coupling constants are observed in di-μ-phenoxido bridged complexes, which is due to the planarity of the Mn-(μ-O)-Gd bridging fragment and to the high Mn-O-Gd angles.

A graceful break-up: serendipitous self-assembly of a ferromagnetically coupled [NiII14] wheel.

The complex [NiII14(HL)(HCOO)Cl(MeOH)(HO)] describes an aesthetically pleasing wheel displaying ferromagnetic nearest neighbour exchange.

An [Fe] molecular oxyhydroxide.

An [Fe] hexagonal bipyramid displays antiferromagnetic exchange between the two capping tetrahedral ions and the six ring octahedral ions resulting in a spin ground state of = 10.

Guest-induced magnetic exchange in paramagnetic [ML] coordination cages.

Paramagnetic complexes that possess magnetically switchable properties show promise in a number of applications. A significantly underdeveloped approach is the use of metallocages, whose magnetic properties can be modulated through host-guest chemistry. Here we show such an example that utilises a simple [CuL] lantern complex.

Photoinduced Jahn-Teller switch in Mn(III) terpyridine complexes.

Ultrafast transient absorption spectra were recorded for [Mn(terpy)X], where X = Cl, F, and N, to explore photoinduced switching from axial to equatorial Jahn-Teller (JT) distortion. Strong oscillations were observed in the transients, corresponding to a wavepacket on the excited-state potential energy surface with oscillation frequency around 115 cm for all three complexes. Multireference quantum chemistry calculations indicate that the reaction coordinate is a pincer-like motion of the terpyridine ligand arising from bond length changes in the excited state due to the JT switch.

Utilizing Raman Spectroscopy as a Tool for Solid- and Solution-Phase Analysis of Metalloorganic Cage Host-Guest Complexes.

The host-guest chemistry of coordination cages continues to promote significant interest, not least because confinement effects can be exploited for a range of applications, such as drug delivery, sensing, and catalysis. Often a fundamental analysis of noncovalent encapsulation is required to provide the necessary insight into the design of better functional systems. In this paper, we demonstrate the use of various techniques to probe the host-guest chemistry of a novel PdL cage, which we show is preorganized to selectively bind dicyanoarene guests with high affinity through hydrogen-bonding and other weak interactions.

Hybrid lanthanide double-deckers based on calixarene and polyoxometalate units.

Complementarity of calixarene (HL) and polyoxometalate ligands results in the first organic-inorganic [ML{MoO(OMe)(NO)}] (M = Y, Gd and Dy) hybrid, directing the formation of a distorted square-antiprismatic MO ligand field and resulting in slow relaxation of the magnetisation for the Dy derivative.