Fine-tuning the single-molecule magnet properties of a [Dy(III)-radical]2 pair.

A supramolecular species composed of a pair of nonequivalent Dy(III)-radical complexes exhibits single-molecule magnet (SMM) properties. The weak effective antiferromagnetic coupling between the Dy(III) ions can be compensated by application of a small (700 Oe) dc field, revealing the relaxation mode of the two distinct SMMs. These unique results illustrate how the dynamics of a supramolecular [Dy-Radical]2 SMM can be fine-tuned by the exchange-bias and an applied magnetic field.

(µ-1,2-dimethoxyethane-κ2O:O')bis[(1,2-dimethoxyethane-κ2O,O')tris(1,1,1,5,5,5-hexafluoro-4-oxopent-2-en-2-olato-κ2O,O')cerium(III)].

A previous analysis [Fatila et al. (2012). Dalton Trans. 41, 1352-1362] of the title complex, [Ce(2)(C(5)HF(6)O(2))(6)(C(4)H(10)O(2))(3)], had identified it as Ce(hfac)(3)(dme)(1.5) according to the (1)H NMR integration [hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate (1,1,1,5,5,5-hexafluoro-4-oxopent-2-en-2-olate) and dme = 1,2-dimethoxyethane]; however, it was not possible to determine the coordination environment unambiguously. The structural data presented here reveal that the complex is a binuclear species located on a crystallographic inversion center. Each Ce(III) ion is coordinated to three hfac ligands, one bidentate dme ligand and one monodentate (bridging) dme ligand, thus giving a coordination number of nine (CN = 9) to each Ce(III) ion. The atoms of the bridging dme ligand are unequally disordered over two sets of sites. In addition, in two of the -CF(3) groups, the F atoms are rotationally disordered over two sets of sites. This is the first crystal structure of a binuclear lanthanide ß-diketonate with a bridging dme ligand.

A 2:1 sulfamethazine-theophylline cocrystal exhibiting two tautomers of sulfamethazine.

In the title cocrystal, 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide-4-amino-N-(4,6-dimethyl-1,2-dihydropyrimidin-2-ylidene)benzenesulfonamide-1,3-dimethyl-7H-purine-2,6-dione (1/1/1), C(7)H(8)N(4)O(2)·2C(12)H(14)N(4)O(2)S, two sulfamethazine molecules cocrystallize with a single molecule of theophylline. Each molecule of sulfamethazine forms a hydrogen-bonded ribbon along the b axis crosslinked by further hydrogen bonding. The two sulfamethazine molecules exhibit a hydrogen-shift isomerization so that the crystal structure contains both tautomeric forms. Calculation of their relative energies showed that the tautomer protonated at the chain N atom is considerably more stable than the one where an N atom in the aromatic ring is protonated. The latter, here observed for the first time, is stabilized through strong intermolecular interactions with the theophylline molecules.

A new polymorph of dichloridotriphenylantimony.

In a new polymorphic form of dichloridotriphenylantimony, [Sb(C(6)H(5))(3)Cl(2)], there are two crystallographically unique molecules in the asymmetric unit and it has been determined that this polymorph is one of two kinetically favoured phases of pure dichloridotriphenylantimony, both of which have Z' > 1. A third polymorph, corresponding to (C(6)H(5))(3)SbCl(1.8)F(0.2), is also known and has Z' = 2. By contrast, the thermodynamically preferred polymorph of pure (C(6)H(5))(3)SbCl(2) has Z' = 1. A brief comparison of the known polymorphic forms of dichloridotriphenylantimony is presented.

A third polymorph of 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl.

The crystal structure of a third polymorphic form of the known 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl radical, C(7)H(3)F(2)N(2)S(2), is reported. This new polymorph represents a unique crystal-packing motif never before observed for 1,2,3,5-dithiadiazolyl (DTDA) radicals. In the two known polymorphic forms of the title compound, all of the molecules form cis-cofacial dimers, such that two molecules are pi-stacked with like atoms one on top of the other, a common arrangement for DTDA species. By contrast, the third polymorph, reported herein, contains two crystallographically unique molecules organized such that only 50% are dimerized, while the other 50% remain monomeric radicals. The dimerized molecules are arranged in the trans-antarafacial mode. This less common dimer motif for DTDA species is characterized by pi-pi interactions between the S atoms [S...S = 3.208 (1) A at 110 K], such that the two molecules of the dimer are related by a centre of inversion. The most remarkable aspect of this third polymorph is that the DTDA dimers are co-packed with monomers. The monomeric radicals are arranged in one-dimensional chains directed by close lateral intermolecular contacts between the two S atoms of one DTDA heterocycle and an N atom of a neighbouring coplanar DTDA heterocycle [S...N = 2.857 (2) and 3.147 (2) A at 110 K].

Anion receptors containing thiazine-1,1-dioxide heterocycles as hydrogen bond donors.

The synthesis, X-ray crystal structures and anion recognition properties of two receptors containing thiazine-1,1-dioxide heterocycles as hydrogen bond donating subunits are reported. The newly synthesized receptors display much different anion selectivities in acetone-d6 than N,N'-diphenyl-1,3-disulfonamidobenzene that was used as a comparison. The selectivity exhibited by one of the new receptors for chloride anions can be attributed to greater steric demand in the cleft formed, in part, by its terminal phenyl rings; an effect that is absent in the comparison receptor.

A double cubane structure in organoplatinum(IV) chemistry.

The reaction of [PtMe2(dpe)], dpe=1,2-di-2-pyridylethane, with hydrogen peroxide occurs with ligand loss to give [{PtMe2(OH)2}n], but the reaction mixture then slowly yields crystals of [{PtMe3OH.PtMe2(OH)2}2][PtMe2(CO3)(dpe)]2, in which the central cluster has an unexpected structure based on a face-bridged double cubane.

Meta-substituted thienyl benzenes: a comparative synthetic, structural and computational study.

A selection of metal-catalyzed C-C bond-forming strategies has been evaluated in the synthesis of a series of meta-substituted thienylbenzenes, (T(n))(2)C(6)H(4) and (T(n))(3)C(6)H(3) (n = 1, 2; T(1) = 2-thienyl; T(2) = 2,2'-bithien-5-yl). Kumada coupling reactions catalyzed by PdCl(2)(dppf) between the appropriate thienyl Grignard and either 1,3- or 1,3,5-bromo- or iodobenzenes were found to be the most reliable in terms of convenience, selectivity and yield (dppf = 1,1'-bis(diphenylphosphino)ferrocene). These conditions also allowed the optimized syntheses of mixed (thienyl)(halo)benzenes, (T(n))C(6)H(3)X(2) and (T(n))(2)C(6)H(3)X (X = Br, I); the latter bromides could be further elaborated in subsequent Stille, Sonogashira, or Kumada reactions to furnish bis(thienyl) compounds bearing electron-donating or -withdrawing groups in the third meta position, (T(n))(2)C(6)H(3)R (R = Ph, p-MeOC(6)H(4), p-FC(6)H(4); n = 1, 2) and (T(1))(2)C(6)H(3)R' (R' = Me, C[triple bond]CPh, Fc; Fc = ferrocenyl). The relative effects of R, R', and n were evaluated by electronic spectroscopy, cyclic voltammetry and calculation. The absorption and emission characteristics and calculated ionization potentials and HOMO-LUMO gaps of these compounds were strongly dependent on n and largely insensitive to R/R'. These measured and calculated properties were also found to be largely invariant with respect to the degree of substitution about the central ring in the meta-substituted benzenes (T(n))(m)X(3-m)C(6)H(3) (m = 1-3; n = 1, 2; X = Br, H), although in the case of n = 1, there was a smooth, albeit small, increase in the emission maximum with increasing thienyl substitution. These findings essentially confirmed earlier theoretical predictions that the thienyl "arms" of meta-substituted phenyl-cored dendrimers were predominantly responsible for absorption and that excitons were localized to the "arms" without any electronic coupling between them, but also introduced the caveat that there was a minimum of two contiguous thiophene rings required for strict exciton localization to the arms. The oxidation potentials of the compounds in solution ranged from 0.9 to 1.6 V and were not rationally dependent on the degree of substitution or the nature of R/R'.

Stability of [2]pseudorotaxanes templated through second-sphere coordination.

A series of nine trans-dichlorobis(pyridine)palladium(II) complexes were prepared (2a-i), containing different 4-substituted pyridine co-ligands. The association constants between these Pd-complexes and 1 were measured, and their values plotted against corresponding sigma(p) degrees values. Measurement of the hydrogen bond acceptor capability of the chloride co-ligands revealed the presence of a linear free energy relationship between the electronic induction of a given 4-substituted pyridine co-ligand and the subsequent complexation strength in [2]pseudorotaxane formation. These trends also extended to trans-dibromobis(pyridine)palladium(II) (3a-e) and trans- dichlorobis(pyridine)platinum(II) complexes (5a-e) when plotted against sigma(p) degrees values. In addition, solid-state structures of three [2]pseudorotaxanes (1.2h, 1.2i, and 1.5e) were determined by single crystal X-ray diffraction further confirming the viability of this template in forming interpenetrated molecular architectures.

Asymmetric ruthenium-catalysed [2+2] cycloadditions between bicyclic alkenes and chiral aryl-substituted acetylenic acyl camphorsultam alkynes.

The regio- and absolute stereochemistry of (7S)-N-[4-(3-thienyl)tricyclo[4.2.1.0(2,5)]non-3-en-3-ylcarbonyl]-2,10-camphorsultam tetrahydrofuran hemisolvate, C(24)H(29)NO(3)S(2).0.5C(4)H(8)O, and (7S)-N-[4-(4-tolyl)tricyclo[4.2.1.0(2,5)]non-3-en-3-ylcarbonyl]-2,10-camphorsultam, C(27)H(33)NO(3)S, have been established. One contains a half-occupancy tetrahydrofuran solvent molecule located on a twofold axis and the other contains two crystallographically unique molecules which are nearly identical. The extended structures of both complexes can be explained via weak C-H...O interactions, which link the molecules together into two-dimensional sheets in the ab plane for the thienyl complex and ultimately into a three-dimensional structure for the tolyl derivative. The stereochemistry of both structures confirms that [2+2] cycloadditions of bicyclic alkenes and alkynes catalysed by ruthenium are exclusively exo.

Isopropyl N-[1'-(methoxy-carbon-yl)ferro-cen-yl]carbamate-ethyl N-[1'-(methoxy-carbon-yl)ferrocen-yl]carbamate (0.6/0.4).

Herein we report the crystal structure and synthesis of two cocrystallized complexes, [Fe(C(7)H(7)O(2))(C(9)H(12)NO(2))](0.6)[Fe(C(7)H(7)O(2))(C(8)H(10)NO(2))](0.4). The molecules crystallize as layers in the bc plane with van der Waals interactions allowing the alkyl chains to interact and the ferrocene units to form a herringbone pattern up the c axis. Every second layer is linked via N-H⋯O hydrogen bonding.The two complexes were modelled as disordered in a ratio of 0.60:0.40.

Dicationic sulfur analogues of N-heterocyclic silylenes and phosphenium cations.

DABling with sulfur: Sulfur(II) dications can be prepared using alpha-diimines to stabilize the positive charge (see scheme; DAB = diazabutadiene, Dipp = 2,6-diisopropylphenyl, OTf = CF(3)SO(3)). The bonding is best described as that of a N,N-chelated sulfur(II) dication; these species represent the first sulfur-based structural mimics of N-heterocyclic silylene compounds and phosphenium cations.

Chiral, hemilabile palladium(II) complexes of tridentate oxazolidines, including C2-symmetric "pincers".

Two classes of diastereomerically enriched chiral tridentate ligands incorporating either two oxazolidine and one pyridine ( 1) or two pyridine and one oxazolidine ( 2a-c) donor groups have been made in a high-yielding modular fashion from readily available enantiopure amino alcohols and aldehydes. Both ligand classes readily formed metal complexes via 1:1 reactions with trans-PdCl 2(PhCN) 2. The compounds Pd( 1)Cl 2 and Pd( 2a-c)Cl 2 were formed as mixtures of 3 and 2 diastereomers, respectively, owing to indeterminate absolute configuration at the C (2) position of their constituent oxazolidine rings. Within each diastereomeric manifold, the metal complexes existed as equilibrium mixtures of bi- and tridentate isomers in solution, the interconversion between which was very rapid even at -50 degrees C. The fluxional nature of the compounds was inferred from a combination of (1)H and (15)N NMR spectroscopic and solution conductivity data. Substitution of one chloride ligand for hexafluorophosphate gave as mixtures of diastereomers the salts [Pd( 1-kappa N,kappa (2) N')Cl]PF 6 ( 8) and [Pd( 2a-c-kappa N,kappa N',kappa N'')Cl]PF 6 ( 12a-c) in which the ligands were coordinated through all three N-donors. A single recrystallization of 8 gave in optically pure form the major diastereomer 8 ( maj ), which was characterized crystallographically. Complexes of 2a-c differed substantially from those of the bis(pyridylmethyl)amine (bpma) ligand family with which they shared direct atom-for-atom connectivity in the coordinating groups. The amines are known to form exclusively the static tridentate complexes [PdCl(bpma-kappa N,kappa (2) N')]Cl; the difference was attributed to torsional strain associated with the rigid oxazolidine ring in tricoordinated 2a-c.

(R)-1-Phenyl-ethanaminium (S)-4-chloro-mandelate.

The absolute configuration of the title complex, C(8)H(12)N(+)·C(8)H(6)ClO(3) (-) or [R-C(6)H(5)C(H)CH(3)NH(3)][S-4-ClC(6)H(4)C(H)(OH)CO(2)], has been confirmed by the structure determination. In the crystal structure, inter-molecular O-H⋯O and N-H⋯O hydrogen bonds form a two-dimensional network perpendicular to the c axis.

A self-associating ADADA hydrogen-bonded double helix.

We report the design, synthesis, and characterization of an oligomer which incorporates a non-coplanar ADADA (hydrogen bond donor/acceptor) array within its structure. The molecule associates through self-complementary hydrogen bonding to form a dimeric double-helical complex.

Organometallic molecular materials: self-assembly through hydrogen bonding of an organoplatinum network structure with zeolite-like topology.

The complex [Pt(OH)(2)Me(2)(dpa)], dpa = di-2-pyridylamine, undergoes a remarkable form of self-assembly through hydrogen bonding in the solid state; there are cyclic tetramer units formed by head-to-head association between pairs of hydroxyl groups, and cyclic hexamer units formed by head-to-tail association between NH and OH groups; these building blocks then self-assemble to form a complex network structure containing large interconnected cavities, reminiscent of zeolites.

Synthesis of a [2]rotaxane through first- and second-sphere coordination.

In an effort to expand the application of a new template from interpenetrated to interlocked molecular species, we report the synthesis of a new [2]rotaxane by means of both first- and second-sphere coordination of a palladium(II) dichloride subunit.

The direct reaction of the tBu-DAB ligand with SeCl4: a redox route to selenium-nitrogen heterocycles.

The reaction of SeCl4 with the ubiquitous tert-butyl-substituted diazabutadiene ligand results in the isolation of a rare example of a 1,2,5-selenadiazolium cation, representing a novel route to Se-N ring formation; these heterocycles can be derivatised at selenium, which has led to the identification of a short Se...N secondary bonding interaction.

Ring-opening polymerisation of coordination compounds: a silver(I) network with both ring and polymer components.

The terpyridyl ligand 2,6-C5H3N{C(=O)N(Me)-4-C5H4N}2, 1, combined with silver(I) salts to give the complexes [Ag2(1)2][BF4]2, 2, and [{Ag3(1)2}n][CF3SO3]3n, 3; the network structure of complex contains both macrocyclic units [Ag2(mu-1)2]2+ and ring-opened polymeric units [{Ag(mu-1)}n]n+.

Crosslinking a palladium(II) polymer gives a laminated sheet structure.

Chains of a zigzag coordination polymer containing bis(pyridyl) bridging groups between palladium(II) centres can be arranged to give a laminated sheet structure by a biomimetic approach in which hydrogen bonding involving amide groups is the key feature.