Bis(tetra­phenyl­arsonium) di-μ-hy­droxido-bis­[(nitrilo­triacetato)­cobalt(III)] octa­hydrate

In the title compound, (C24H20As)2[Co2(C6H6NO6)2(OH)2]·8H2O, the CoIII atom in the binuclear centrosymmetric anion is octa­hedrally surrounded by one N atom and three O atoms of the tetra­dentate nitrilo­triacetate ligand and two μ-hydroxide ligands. The crystal packing is controlled by C—H⋯O and O—H⋯O hydrogen-bonding inter­actions. The crystal employed in this study proved to be a two-component twin around (01)

2,5-Dioxopyrrolidin-1-yl adamantane-1-carboxyl­ate

The title compound, C15H19NO4, contains one crystallographically independent mol­ecule in the asymmetric unit. The N—O—C—O torsion angle is 1.97 (9)°. The two pairs of vicinal H atoms that lie above or below the plane defined by the five-membered pyrrolidine-2,5-dione ring are an average of 6.57 (5)° from being eclipsed. The average absolute C—C—C—C torsion angle in the adamantane skeleton, in which each fused cyclo­hexane ring is in a chair configuration, is 59.99 (5)°. The crystal packing is unremarkable

Hierarchical assembly of discrete copper(ii) metallo-structures from pre-assembled dinuclear (bis-beta-diketonato)metallocycles and flexible difunctional co-ligands

The sequential interaction of preformed [Cu(L) (THF)] (where HL is 1,1-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione incorporating a 1,3-phenylene linker between its two β-diketone domains) and [Cu (L)]·2HO (where H L is 1,1-(4,4′-oxybiphenylene)-bis(4,4- dimethylpentane-1,3-dione) incorporating a flexible oxybiphenylene linkage between the two β-diketone groups) with the potentially difunctional aliphatic non-planar co-ligands, N-methylpiperazine (mpip), N,N′- dimethylpiperazine (dmpip) and 1,4-thiomorpholine (thiomorph) is reported. A series of extended molecular assemblies exhibiting a range of di- and tetranuclear assemblies were obtained and their X-ray structures determined. Dinuclear [Cu(L)(mpip)] ·2mpip incorporates two 5-coordinate, square pyramidal metal centres as does tetranuclear [{Cu(L)} (dmpip)]·2dmpip. In contrast, dinuclear [Cu (L)(dmpip)]·dmpip and [{Cu(L)}(thiomorph) ]·3thiomorph each contain two 5-coordinate and two 6-coordinate centres. Each of [Cu(L)(THF) ]·2THF and Cu(L)(mpip) ]·HO incorporate only 5-coordinate metal centres, with the latter complex forming a one-dimensional hydrogen bonded ribbon-like structure directed along the crystallographic a-axis. In keeping with the documented tendency for the smallest, least strained assembly to form in supramolecular self-assembly processes, the incorporation of the flexible "oxy" linkage between the 4,4′-linked phenylene rings of H L results in generation of a dinuclear [Cu L] species rather than a trinuclear (triangular) [CuL] species of the type formed by the more rigid bis-β-diketonato ligand analogue in which the biphenylene rings separating the β-diketone domains are directly coupled in their 4,4′ positions

Solid-state and solution-phase conformations of pseudoproline-containing dipeptides

The conformations of 14 threonine-derived pseudoproline-containing dipeptides (including four d-allo-Thr derivatives) have been investigated by NMR. In solution, the major conformer observed for all dipeptides is that in which the amide bond between the pseudoproline and the preceding amino acid is cis. For dipeptides in which the N-terminus is protected, the ratio of cis- to trans-conformers does not depend significantly on the side chain of the N-terminal amino acid, or the stereochemistry of the Thr residue. However, for dipeptides bearing a free N-terminus, there are significant differences in the ratios of cis- to trans-conformers depending on the side chain present. Three dipeptides were crystallized and their X-ray structures determined. In two cases, (benzyloxycarbonyl (Cbz)-Val-Thr(ΨMe,Mepro)-OMe and Cbz-Val-Thr(ΨMe,Mepro)-OH), the dipeptides adopt a trans-conformation in the solid state, in contrast to the structures observed in solution. In the third case, (9-fluorenylmethoxycarbonyl (Fmoc)-Val-d-allo-Thr(ΨMe,Mepro)-OH), a cis-amide geometry is observed. These structural differences are attributed to crystal-packing interactions

A mixed valent heterometallic Cu-II/Na-I coordination polymer with sodium-phenyl bonds

A mixed valent heterometallic Cu/Na coordination polymer (1) is generated by the reaction of a Schiff base ligand, (6,6′-(1E,1′E)-(2-hydroxypropane-1,3-diyl)bis(azan-1-yl-1-ylidene) bis(methan-1-yl-1-ylidene)bis(2-methoxyphenol)) with copper(ii) acetate and sodium perchlorate. In addition to the presence of alcohol oxygen-sodium coordination bonds, the single crystal X-ray structure reveals that the 1D coordination polymer is stabilised by the formation of phenyl-sodium η-bonds, face-to-face π-π contacts and Cu-π interactions. This journal i

Reversible pressure-controlled depolymerization of a copper(II)-containing coordination polymer

A unique pressure-induced Cu-N bond breaking/bond forming reaction is reported. The variation of pressure on a single crystal of a one-dimensional copper- (II)-containing coordination polymer (Cu2 L2 (1-methylpiperazine)2 ]n , where H2 L is 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione)), was monitored using single crystal X-ray diffraction with the aid of a diamond anvil cell. At a very low elevated pressure (≈0.05 GPa) a remarkable reversible phase change was observed. The phase change results in the depolymerization of the material through the cleavage and formation of axial Cu-N bonds as well as "ring flips" of individual axially coordinated 1-methylpiperazine ligands. Overall, the pressure-induced phase change is associated with a surprising (and non-intuitive) shift in structure-from a 1-dimensional coordination polymer to a discrete dinuclear complex

Mono- and dinucleating Ni(II), Cu(II), Zn(II) and Fe(III) complexes of symmetric and unsymmetric Schiff bases incorporating salicylimine functions - Synthetic and structural studies

The known Schiff base, 3-(2-aminophenylamino)-1-phenylbut-2-en-1-one (1), formed by 1:1 condensation of o-phenylenediamine and benzoylacetylacetone reacts at its free amine site with salicylaldehyde and 5-tert-butylsalicylaldehyde in the presence of Ni(II) and Cu(II) acetates, or with 5-tert-butylsalicylaldehyde in the presence of Zn(II) acetate, to generate 1:1 (M:L) diimine complexes (2) of the corresponding doubly deprotonated, unsymmetric, O2N 2-tetradentate ligands. In contrast, reaction of Zn(II) acetate with 1 and salicylaldehyde led to Schiff base exchange (with loss of benzoylacetylacetone) to yield symmetric [ZnL3] [where L3 is N,N′-o-phenylenebis(salicyliminato)]. Similarly, when Fe(II) chloride was substituted for metal acetate in the reaction of 1 with 5-tert-butyl- salicylaldehyde and the initial product crystallised in the presence of dabco (as base), a related Schiff base exchange reaction occurred along with aerial oxidation of the Fe(II) to produce the neutral dinuclear [Fe III(L4)2(μ-O)] species [where L4 is N,N′-o-phenylenebis(5-tert-butylsalicyliminato)] in which Fe(III) centres are linked by an oxo group to produce two 5-coordinate Fe(III) centres; pairs of these (oxo-bridged) dinuclear complex units are further linked via elongated intermolecular Fe-Ophenolic contacts (Fe-O, 2.44 Å) to form an unusual tetranuclear supramolecular cluster. This complex was also synthesised directly by the in situ reaction of 5-tert-butyl-salicylaldehyde, o-phenylenediamine and Fe(II) chloride (2:1:1 mol ratio) in air. In an extension of these studies, the in situ reaction of the 1,3-aryl linked bis-β-diketone, 1,1-(1,3-phenylene)-bis-butane-1,3-dione), o-phenylenediamine, salicylaldehyde and Ni(II) acetate in a 1:2:2:2 ratio yielded [Ni2L5], the dinuclear analogue of the unsymmetric mononuclear Ni(II) complex 2, in which each nickel centre has a square planar environment. Reaction of the above 1,3-phenylene linked bis-β-diketone precursor with o-phenylenediamine in a 1:2 M ratio yields 1,3-bis(4-methyl-3H- benzo[b][1,4]diazepin-2-yl)benzene as its monohydrate (3·H2O) incorporating two 7-membered diaza heterocyclic rings; thus contrasting with the 'open' Schiff base structure observed for 1. X-ray structures of 1, 3·H2O, [NiL1]·py, [NiL1] ·EtOH, [NiL2], [CuL1]·py, [CuL 1]·0.5CHCl3, [(FeL4)2(μ-O) ]2·1.5THF·0.4EtOH·0.6H2O and [NiL5]·0.25EtOH·0.125py are reported

Nickel(II) and iron(II) triple helicates assembled from expanded quaterpyridines incorporating flexible linkages

In the present study the interaction of Fe(II) and Ni(II) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5'-methyl-[2,2']bipyridinyl-5-ylmethoxy)benzene ligands (4–6 respectively), incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains, was shown to predominantly result in the assembly of [M2L3]4+ complexes; although with 4 and 6 there was also evidence for the (minor) formation of the corresponding [M4L6]8+ species. Overall, this result contrasts with the behaviour of the essentially rigid 'parent' quaterpyridine 1 for which only tetrahedral [M4L6]8+ cage species were observed when reacted with various Fe(II) salts. It also contrasts with that observed for 2 and 3 incorporating essentially rigid substituted phenylene and biphenylene bridges between the dipyridyl domains where reaction with Fe(II) and Ni(II) yielded both [M2L3]4+ and [M4L6]8+ complex types, but in this case it was the latter species that was assigned as the thermodynamically favoured product type. The X-ray structures of the triple helicate complexes [H2O⊂Ni2(4)3](PF6)4·THF·.2H2O, [Ni2(6)3](PF6)4·195MeCN·1.THF·1.82O, and the very unusual triple helicate PF6− inclusion complex, [(PF6)⊂Ni2(5)3](PF6)3·1.75eCN·5.25TF·0.25H2O are reported

New discrete and polymeric supramolecular architectures derived from dinuclear Co(II), Ni(II) and Cu(II) complexes of aryl-linked bis-beta-diketonato ligands and nitrogen bases: synthetic, structural and high pressure studies

New examples of nitrogen base adducts of dinuclear Co(II), Ni(II) and Cu(II) complexes of the doubly deprotonated forms of 1,3-aryl linked bis-β-diketones of type [RC([double bond, length as m-dash]O)CH2C([double bond, length as m-dash]O)C6H4C([double bond, length as m-dash]O)CH2C([double bond, length as m-dash]O)R] (L1H2) incorporating the mono- and difunctional amine bases pyridine (Py), 4-ethylpyridine (EtPy), piperidine (pipi), 1,4-piperazine (pip), N-methylmorpholine (mmorph), 1,4-dimethylpiperazine (dmpip) and N,N,N′,N′-tetramethylethylenediamine (tmen) have been synthesised by reaction of the previously reported [Cu2(L1)2]·2.5THF (R = Me), [Cu2(L1)2(THF)2] (R = t-Bu), [Ni2(L1)2(Py)4] (R = t-Bu) and [Co2(L1)2(Py)4] (R = t-Bu) complexes with individual bases of the above type. Comparative X-ray structural studies involving all ten base adduct derivatives have been obtained and reveal a range of interesting discrete and polymeric molecular architectures. The respective products have the following stoichiometries: [Cu2(L1)2(Py)2]·Py (R = Me), [Cu2(L1)2(EtPy)2]·2EtPy (R = t-Bu), [Cu2(L1)2(pipi)2]·2pipi (R = t-Bu), [Cu2(L1)2(mmorph)2] (R = t-Bu), [Cu2(L1)2(tmen)2] (R = t-Bu) and {[Cu2(L1)2(pip)]·pip·2THF}n, [Co2(L1)2(tmen)2] (R = t-Bu), [Ni2(L1)2(Py)4]·dmpip (R = t-Bu), [Ni2(L1)2(pipi)4]·pipi (R = t-Bu) and [Ni2(L1)2(tmen)2] (R = t-Bu). The effect of pressure on the X-ray structure of [Cu2(L1)2(mmorph)2] has been investigated. An increase in pressure from ambient to 9.1 kbar resulted in modest changes to the unit cell parameters as well as a corresponding decrease of 6.7 percent in the unit cell volume. While a small ‘shearing’ motion occurs between adjacent molecular units throughout the lattice, no existing bonds are broken or new bonds formed

New nickel(II) and iron(II) helicates and tetrahedra derived from expanded quaterpyridines

As an extension of prior studies involving the linear quaterpyridine ligand, 5,5'''-dimethyl-2,2':5',5'':2'',2'''-quaterpyridine 1, the synthesis of the related expanded quaterpyridine derivatives 2 and 3 incorporating dimethoxy-substituted 1,4-phenylene and tetramethoxy-substituted 4,4'-biphenylene bridges between pairs of 2,2'-bipyridyl groups has been carried out via double-Suzuki coupling reactions between 5-bromo-5'-methyl-2'-bipyridine and the appropriate di-pinacol-diboronic esters using microwave heating. Reaction of 2 and 3 with selected Fe(II) or Ni(II) salts yields a mixture of both [M2L3]4+ triple helicates and [M4L6]8+ tetrahedra, in particular cases the ratio of the products formed was shown to be dependent on the reaction conditions; the respective products are all sufficiently inert to allow their chromatographic separation and isolation. Longer reaction times and higher concentrations were found to favour tetrahedron formation. The X-ray structures of solvated [Ni2(2)3](PF6)4, [(PF6) ⊂ Fe4(2)6](PF6)7, [Fe4(3)6](PF6)8 and [Ni4(3)6](PF6)8 have been determined, while the structure of the parent Fe(II) cage in the series, [(PF6) ⊂ Fe4(1)6](PF6)7, was reported previously. The internal volumes of the Fe(II) tetrahedral cages have been calculated and increase from 102 Å3 for [Fe4(1)6]8+ to 227 Å3 for [Fe4(2)6]8+ to 417 Å3 for [Fe4(3)6]8+ and to an impressive 839 Å3 for [Ni4(3)6]8+. The corresponding void volume in the triple helicate [Ni2(2)3]4+ is 29 Å3