Mechanisms of formation of pseudocalixarene Schiff base macrocycles investigated by ESI-MS

Starting from 4-substituted phenols, three dialdehydes were synthesised as Schiff base pseudocalixarene macrocyclic precursors. Two of the dialdehydes, 2,2’–methylene-bis- [(6-hydroxymethyl)-4-methylphenol] and 2,2’–methylene-bis-[(6-hydroxymethyl)-4- phenylphenol] were structurally characterised. For the phenyl substituted compound condensation with 1,3-diaminopropan-2-ol, with transition metal ions as template, was investigated and a series of dinuclear complexes was synthesised and characterised by IR, FAB-MS and elemental analysis. The analytical data implied that the complexes have the same saddle shape conformation controlled by hydrogen bonds resulting from mono-deprotonation of the methylendiphenol units as was observed in previous work. A range of TM2M trinuclear complexes [TM = Cu(II), Ni(II) and M = Li(I), Na(I), Mg(II), Ca(II)] of (2+2) macrocycles was synthesised and characterised by IR, MS (FAB, ESI) and elemental analysis. Additionally [Cu2Ca(2+2)(NO3)2](MeOH)2 was characterised by X-ray crystallography. An ESI-MS was used to follow condensation reactions between 2,2’–methylene-bis-[(6- hydroxymethyl)-4-tert-butylphenol] and 1,3-diaminopropan-2-ol in solution with various templates. It was found that, when a transition metal is used alone, the reaction produces only the (2+2) macrocycle. Cu(II) produced equilibrium mixtures containing dicopper(II) and tricopper(II) species but Ni(II) and Zn(II) yielded only dinuclear complexes. When transition metal ions were used in combination with group 1 or group 2 metal ions, the size of the macrocycle and nuclearity of the complex depended on the synthetic route and nature of alkali or alkaline earth metal. Among the products identified in the ESI-MS spectra were trinuclear complexes of the (2+2) macrocycle, pentanuclear sandwich complexes of two (2+2) macrocycles, tetranuclear (3+3) complexes, pentanuclear (4+4) and hexanuclear (6+6) species. One of the routes resulted in formation of [BaCu4(4+4)]2+ ion via a [BaCu4(dialdehyde)4]2+ cluster which was established to be a double template process where both metals are necessary for formation of the macrocycle. The central Ba(II) ion holds the dialdehydes together and the Cu(II) ion orients the carbonyl groups for Schiff base condensation

Data to Support Iron(II) Complexes of 2,6-Bis(imidazo[1,2?a]pyridin-2-yl)pyridine and Related Ligands with Annelated Distal Heterocyclic Donors

Complexes of the title ligand and two of its derivatives are mostly high-spin in the solid state, but exhibit thermal spin-crossover equilibria in solution with a ligand-centred room-temperature emission

Data to support study of Iron/2,6-Di(pyrazol-1-yl)pyridine Derivatives with a Discotic Pattern of Alkyl or Alkynyl Substituents

[Fe(1-bpp)2][BF4]2 derivatives with four long chain alkyl substituents show an irreversible low→high-spin conversion near 350 K, which may reflect melting of the complexes' alkyl substituent conformation

Data to support study of The Structures and Spin States of Iron(II) Complexes of Isomeric 2,6-Di(1,2,3-triazolyl)pyridine Ligands

Different isomers of the title ligands coordinate to iron(II) in monodentate or tridentate fashion, leading to complexes with a variety of spin state properties

Structures and Spin States of Crystalline [Fe(NCS)2L2] and [FeL3]2+ Complexes (L = an Annelated 1,10-Phenanthroline Derivative)

The phase behaviour and spin states of [Fe(NCS)2(dpq)2] (1; dpq = dipyrido[3,2-f:2′,3′-h]quinoxaline), [Fe(NCS)2(dppz)2] (2; dppz = dipyrido[3,2-a:2′3′-c]phenazine) and [Fe(NCS)2(dppn)2] (3; dppn = dipyrido[3,2-a:2′3′-c]benzophenazine) have been investigated. Solvent-free 1 and 2 are isostructural and low-spin in the crystalline state, in contrast to previously published 2·py (py = pyridine) which exhibits a hysteretic spin-crossover (SCO) transition near 140 K. The inactivity of 1 and 2 towards SCO may relate to their more crowded intermolecular lattice environment, particularly two very short intermolecular anion⋯π contacts involving the NCS− ligands. Two solvate phases of 1 are also described, including 1·2py which undergoes gradual SCO with T½ca. 188 K. Bulk samples of 2 and 3 are predominantly low-spin and isostructural with the crystals of 2 by powder diffraction, but bulk samples of 1 contain an extra phase that exhibits hysteretic SCO, but was not crystallographically characterised. Crystal structures of low-spin [Fe(dppz)3][ClO4]2 (4) and a solvate of [Fe(dppn)3][BF4]2 (5) are also described, which are the first homoleptic complexes of these ligands to be crystallographically characterised

Molecular Squares, Coordination Polymers and Mononuclear Complexes Supported by 2,4-Dipyrazolyl-6H-1,3,5-triazine and 4,6-Dipyrazolylpyrimidine Ligands

The Fe[BF4]2 complex of 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine (L1) is a high-spin molecular square, [{Fe(L1)}4(μ-L1)4][BF4]8, whose crystals also contain the unusual HPzBF3 (HPz = pyrazole) adduct. Three other 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine derivatives with different pyrazole substituents (L2-L4) are unstable in the presence of first row transition ions, but form mononuclear, polymeric or molecular square complexes with silver(I). Most of these compounds involve bis-bidentate di(pyrazolyl)triazine coordination, which is unusual for that class of ligand, and the molecular squares encapsulate one or two BF4‒, ClO4‒ or SbF6‒ ions through combinations of anion...π, Ag...X and/or C‒H...X (X = O or F) interactions. Treatment of Fe[NCS]2 or Fe[NCSe]2 with 4,6-di(pyrazol-1-yl)-2H-pyrimidine (L5) or its 2-methyl and 2-amino derivatives L6 and L7) yields mononuclear [Fe(NCE)2L2] and/or the 1D coordination polymers catena-[Fe(NCE)2(μ-L)] (E = S or Se, L = L5-L7). Alcohol solvates of isomorphous [Fe(NCS)2L2] and [Fe(NCSe)2L2] compounds show different patterns of intermolecular hydrogen bonding, reflecting the acceptor properties of the anion ligands. These iron compounds are all high-spin, although annealing solvated crystals of [Fe(NCSe)2(L5)2] affords a new phase exhibiting an abrupt, low-temperature spin transition. Catena-[Fe(H2O)2(μ-L5)][ClO4]2 is a coordination polymer of alternating cis and trans iron centres

Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence.

Reaction of 2,6-difluoropyridine with 2 equiv of indazole and NaH at room temperature affords a mixture of 2,6-bis(indazol-1-yl)pyridine (1-bip), 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine (1,2-bip), and 2,6-bis(indazol-2-yl)pyridine (2-bip), which can be separated by solvent extraction. A two-step procedure using the same conditions also affords both 2-(indazol-1-yl)-6-(pyrazol-1-yl)pyridine (1-ipp) and 2-(indazol-2-yl)-6-(pyrazol-1-yl)pyridine (2-ipp). These are all annelated analogues of 2,6-di(pyrazol-1-yl)pyridine, an important ligand for spin-crossover complexes. Iron(II) complexes [Fe(1-bip)2](2+), [Fe(1,2-bip)2](2+), and [Fe(1-ipp)2](2+) are low-spin at room temperature, reflecting sterically imposed conformational rigidity of the 1-indazolyl ligands. In contrast, the 2-indazolyl complexes [Fe(2-bip)2](2+) and [Fe(2-ipp)2](2+) are high-spin in solution at room temperature, whereas salts of [Fe(2-bip)2](2+) exhibit thermal spin transitions in the solid state. Notably, [Fe(2-bip)2][BF4]2·2MeNO2 adopts a terpyridine embrace lattice structure and undergoes a spin transition near room temperature after annealing, resulting in thermal hysteresis that is wider than previously observed for this structure type (T1/2 = 266 K, ΔT = 16-20 K). This reflects enhanced mechanical coupling between the cations in the lattice through interdigitation of their ligand arms, which supports a previously proposed structure/function relationship for spin-crossover materials with this form of crystal packing. All of the compounds in this work exhibit blue fluorescence in solution under ambient conditions. In most cases, the ligand-based emission maxima are slightly red shifted upon complexation, but there is no detectable correlation between the emission maximum and the spin state of the iron centers

Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes

Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N’-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in acetone yielded the corresponding [FeL2][BF4]2 complex salts. Four of the new ligands and four of the complexes have been crystallographically characterised. Particularly noteworthy are two polymorphs of [Fe(L3)2][BF4]2·2MeNO2 (L3 = 3,4-dimethoxyphenyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), one of which is crystallographically characterised as high-spin while the other exhibits the onset of spin-crossover above room temperature. The other complexes are similarly low-spin at low temperature but exhibit gradual spin-crossover on heating, except for an acetone solvate of [Fe(L5)2][BF4]2 (L5 = benzyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), which exhibits a more abrupt spin-transition at T½ = 273 K with 9 K thermal hysteresis

Gradual Thermal Spin-Crossover Mediated by a Reentrant <i>Z</i>′ = 1 → <i>Z</i>′ = 6 → <i>Z</i>′ = 1 Phase Transition

The Fe­[BF₄]₂ complex of the Schiff base podand tris­[4-(thiazol-4-yl)-3-aza-3-butenyl]­amine exhibits gradual thermal spin-crossover with <i>T</i>_1/2 ≈ 208 K in the solid state. A weak discontinuity in the magnetic susceptibility curve at 190 K is associated with a reentrant symmetry-breaking transition involving a trebling of the unit cell volume (from <i>P</i>2₁/<i>c</i>, <i>Z</i> = 4, to <i>P</i>2₁, <i>Z</i> = 12). The intermediate phase contains six independent cations in puckered layers of low-spin, and high-spin or mixed-spin, molecules with an overall 30% high-spin population at 175 K

Double template effect in [4+4] Schiff base macrocycle formation: an ESI-MS study

The mechanism of self-assembly of a polynuclear complex of a [4 + 4] Schiff base iminomethylenediphenolate macrocycle [BaCu4(4 + 4)]2+ via a non-macrocyclic dialdehyde intermediate has been followed using ESI-MS of the reaction solutions. Both assembly of the intermediate and Schiffbase condensation with diamine give rise to single products; formation of the intermediate metallacycle is fast but Schiffbase condensation ismuch slower. Both intermediate complex andmacrocyclic product have been structurally characterised