Synthesis of nitrogen mustards on cobalt(III).

Bis(bidentate) and bis(tridentate) Co(III) complexes of N-(2-hydroxyethyl)ethane-1,2-diamine (heen), 2-[(2-aminoethyl)amino]ethan-1-olate (heen-H), or N-(2-chloroethyl)ethane-1,2-diamine (ceen) ligands have been synthesised, and a range of reaction conditions established for their syntheses by different routes. They can all be ultimately derived from (OC-6-12')-[Co(heen)2(NO2)2]NO3 and provide access to the trans amine trans chloride nitrogen mustard complex, (OC-6-12')-[Co(ceen)2(Cl)2]Cl. Although complex isomeric mixtures were obtained from the reaction of (OC-6-12')-[Co(heen)2(NO2)2]NO3 under different reaction conditions, ultimately, the trans amine trans chlorido configuration around the Co(III) metal centre of the (OC-6-12')-[Co(ceen)2(Cl)2]Cl complex was favoured.

Approaching the isotropic spin-ladder regime: structure and magnetism of all-pyrazine-bridged copper(II)-based antiferromagnetic ladders.

The crystal structure and magnetic properties of two all-pyrazine-bridged antiferromagnetic spin ladders are reported. The complexes, catena-(bis(3-X-4-pyridone)(µ-pyrazine)copper(II)(-µ-pyrazine)diperchlorate ([Cu(pz)1.5(L)2](ClO4)2 where L = 3-X-4-pyridone and X = Br (1) or Cl (2)), contain copper(II)-based ladders in which both the rung and rail bridges are pyrazine molecules bonded through the x2-y2 orbital of the copper(II) ions. This structural scaffold is proposed to approach the isotropic spin-ladder regime. 1 and 2 crystallize in the monoclinic space group P21/c. Due to the bulk of the 3-X-4-HOpy ligands, the ladders are well isolated in the a-direction (1, 15.6 Å; 2, 15.5 Å). The ladders, which run in the b-direction, are stacked in the c-direction with the separation (1, 7.87 Å; 2, 7.82 Å) between copper(II) ions caused by the bulk of a semi-coordinate perchlorate ion coordinated in the axial position. Computational evaluation of magnetic JAB couplings between Cu-moieties of 2 supports the experimentally proposed magnetic topology and agrees with an isolated isotropic spin-ladder (Jrail = -4.04 cm-1 (-5.77 K) and Jrung = -3.89 cm-1 (-5.56 K)). These complexes introduce a convenient scaffold for synthesizing isotropic spin-ladders with modest superexchange interactions, the strength of which may be tuned by variations in L. The magnetic susceptibility down to 1.8 K, for both compounds, is well described by the strong-rung ladder model giving nearly isotropic exchange with Jrung ≈ Jrail ≈ -5.5 K (1) and -5.9 K (2) using the Hamiltonian. Theoretical simulations of the magnetic response of 2 using the isotropic ladder model are in excellent agreement with experiment. The measured magnetization to 5 T indicates a quantum-dominated magnetic spectrum. Again, calculated lower and saturation (4.3 and 24 T, respectively) critical fields for 2 are consistent with experimental measurements, and magnetization data at very low temperatures indeed suggest the presence of quantum effects. Further, the computational study of short- and long-range spin ordering indicates that a 2D-to-3D crossover might be feasible at lower temperatures. Analysis of the Boltzmann population corroborates the presence of accessible triplet states above the singlet ground state enabling the aforementioned 2D-to-3D crossover.

Pyrazine-bridged Cu(ii) chains: diaquabis(n-methyl-2-pyridone)copper(ii) perchlorate complexes.

A family of pyrazine-bridged, linear chain complexes of Cu(ii) of the formula [CuL2(H2O)2(pz)](ClO4)2 [pz = pyrazine; L = n-methyl-2(1H)-pyridone, n = 3 (1), 5 (2), and 6 (3)] has been prepared. Single-crystal X-ray diffraction shows six-coordinate, pyrazine-bridged chains with trans-pairs of ancillary ligands. The substituted pyridine molecules exist in their pyridone tautomers and are coordinated through the carbonyl oxygen atom. The structure is stabilized by intramolecular hydrogen bonds between the pyridone and water molecule, and via hydrogen bonds between the water molecules and perchlorate ions. 2 undergoes a crystallographic phase transition between C2/c (high temperature phase) and P1[combining macron] (low temperature phase). Powder EPR spectra reveal that all complexes are rhombic, although differences between gx and gy can only be seen clearly at Q-band. Variable temperature magnetic susceptibility data show antiferromagnetic interactions and the data were fit to the uniform chain model yielding J/kB = -9.8, -9.2 and -11 K for 1-3 respectively. Attempts to model an interchain interaction strength indicate that the chains are very well isolated.

Ferromagnetic Exchange in Bichloride Bridged Cu(II) Chains: Magnetostructural Correlations between Ordered and Disordered Systems.

The synthesis, structure, magnetic properties, and theoretical analysis of a new phase of dichloro(2-chloro-3-methylpyridine)copper(II) (2) and its isomorphous analogue dichloro(2-bromo-3-methylpyridine)copper(II) (3) are reported. Both complexes crystallize in the orthorhombic space group Pbca and present square pyramidal Cu(II) ions bridged into chains by chloride ions with each copper(II) bearing a single pyridine ligand. Variable temperature magnetic susceptibility measurements were well fit by a uniform one-dimensional ferromagnetic chain model with 2, J = 69.0(7) K, C = 0.487 emu-K/mol-Oe; 3, J = 73.9(4) K, C = 0.463 emu-K/mol-Oe (H = -JΣSi·Sj Hamiltonian). The experimental J-values were confirmed via theoretical calculations. Comparison to a known disordered polymorph of dichloro(2-chloro-3-methylpyridine)copper(II), 1, shows marked differences as there are significant antiferromagnetic next-nearest neighbor interactions in 1 in addition to randomness induced by the disorder which provide a distinctly different magnetic response. The differences in magnetic behavior are attributed principally to the structural difference in the Cu(II) coordination sphere, 1 being significantly closer to trigonal-bipyramidal, whose difference changes both the nearest and next-nearest neighbor interactions.

S=1/2 one-dimensional random-exchange ferromagnetic zigzag ladder, which exhibits competing interactions in a critical regime.

The synthesis, crystal structure, and magnetic properties (from a combined experimental and First-Principles Bottom-Up theoretical study) of the new compound catena-dichloro(2-Cl-3Mpy)copper(II), 1, [2-Cl-3Mpy=2-chloro-3-methylpyridine] are described and rationalized. Crystals of 1 present well isolated magnetic 1D chains (no 3D order was experimentally observed down to 1.8 K) and magnetic frustration stemming from competing ferromagnetic nearest-neighbor (J(NN)) interactions and antiferromagnetic next-nearest neighbor (J(NNN)) interactions, in which α=J(NNN)/J(NN) <-0.25. These magnetic interactions give rise to a unique magnetic topology: a two-leg zigzag ladder composed of edge-sharing up-down triangles with antiferromagnetic interactions along the rails and ferromagnetic interactions along the zigzag chain that connects the rails. Crystals of 1 also present a random distribution of the 2-Cl-3Mpy groups, which are arranged in two different orientations, each with a 50 % occupancy. This translates into a random static structural disorder within each chain by virtue of which the value of the J(NN) magnetic interactions can randomly take one of the following three values: 53, 36, and 16 cm(-1). The structural disorder does not affect the J(NNN) value, which in all cases is approximately -9 cm(-1). A proper statistical treatment of this disorder provides a computed magnetic susceptibility curve that reproduces the main features of the experimental data.

3,4-Dihydroxy-1,6-bis(4-methoxyphenyl)hexa-2,4-diene-1,6-dione, its 4-methylphenyl analogue, and a potassium salt of 2-hydroxy-4-(4-methoxyphenyl)-4-oxobut-2-enoic acid.

Reaction of 4-methoxyacetophenone with diethyl oxalate under basic conditions produced 3,4-dihydroxy-1,6-bis(4-methoxyphenyl)hexa-2,4-diene-1,6-dione, C20H18O6, (1). The molecules lie across a crystallographic inversion centre and intramolecular hydrogen bonding, similar to acetylacetone, is observed, confirming that the molecule is in the di-enol-dione tautomeric form. Additional O-H...O hydrogen bonds link the molecules into chains parallel to the b axis. The structure is compared with that of redetermined 4-methylphenyl compound 3,4-dihydroxy-1,6-bis(4-methylphenyl)hexa-2,4-diene-1,6-dione, C20H18O4, (2), which crystallizes in a similar fashion. The salt, catena-poly[[µ2-2-hydroxy-4-(4-methoxyphenyl)-4-oxobut-2-enoato-κ(3)O(1),O(2):O(4)][µ2-2-hydroxy-4-(4-methoxyphenyl)-4-oxobut-2-enoic acid-κ(2)O(1):O(4)]potassium], [K(C11H9O5)(C11H10O5)]n, (3), was isolated as a by-product of the synthesis of (1). The two organic species are linked by a strong hydrogen bond between the carboxylic acid and carboxylate groups. They are further stabilized and linked into a double-chain structure via the seven-coordinate potassium ion.

2-Amino-5-iodopyridinium bromide hemihydrate and 2-amino-5-iodopyridinium chloride monohydrate.

The hydrobromide and hydrochloride salts of 2-amino-5-iodopyridine were prepared from aqueous solutions. The hydrobromide salt, C5H6IN2(+)·Br(-)·0.5H2O, crystallizes as a hemihydrate, and exhibits hydrogen bonding and π-stacking which stabilize the crystal structure. The hydrochloride salt, C5H6IN2(+)·Cl(-)·H2O·0.375HCl, crystallized as the hydrate and exhibits similar hydrogen bonding and π-stacking in the lattice. The most interesting feature of the hydrochloride salt is the presence of an additional fractional HCl molecule which introduces disorder in the location of the water molecule. The additional proton from the fractional HCl molecule is accounted for by the presence of a partial hydronium ion on one of the water sites.

Hexaaqua-copper(II) bis-(tetra-fluorido-borate)-pyrazine 1,4-dioxide (1/3).

The crystal structure of the title compound, [Cu(H2O)6](BF4)2·3C4H4N2O2, comprises discrete [Cu(H2O)6](2+) cations and BF4 (-) anions along with three equivalents of pyrazine 1,4-dioxide (pzdo). The hexa-aqua-copper(II) ion and all three pzdo mol-ecules lie about crystallographic inversion centers. The lattice is supported by an extensive hydrogen-bonding network. O-H⋯O hydrogen bonding between the [Cu(H2O)6](2+) and pzdo units creates a pseudo-hexa-gonal lattice parallel to the bc plane. The BF4 (-) anions lie in the voids of that lattice, held in place by O-H⋯F hydrogen bonds, and also generate BF4 (-)-pzdo-BF4 (-)-pzdo stacks via short F⋯N contacts [2.866 (3)-3.283 (4) Å].

Aqua-(azido)[N-(pyridin-2-ylcarbon-yl)pyridine-2-carboxamido-κ(3) N,N',N'']copper(II).

The title compound, [Cu(C12H8N3O2)(N3)(H2O)], was formed by the air oxidation of 2-(amino-meth-yl)pyridine in 95% ethanol in the presence of copper(II) nitrate and sodium azide with condensation of the resulting picolinamide mol-ecules to generate the imide moiety. The Cu(II) ion has a square-pyramidal coordination sphere, the basal plane being occupied by four N atoms [two pyridine (py) N atoms, the imide N atom and an azide N atom] in a nearly planar array [mean deviation = 0.048 (6) Å] with the Cu(II) ion displaced slightly from the plane [0.167 (5) Å] toward the fifth ligand. The apical position is occupied by a coordinating water mol-ecule [Cu-O = 2.319 (4) Å]. The crystal structure is stabilized by hydrogen-bonding inter-actions between the water mol-ecules and carbonyl O atoms. The inversion-related square-pyramidal complex molecules pack base-to-base with long Cu⋯Npy contact distances of 3.537 (9) Å, preventing coordination of a sixth ligand.

Synthesis, structure, magnetic behavior, and theoretical analysis of diazine-bridged magnetic ladders: Cu(quinoxoline)X2 and Cu(2,3-dimethylpyrazine)X2 (X = Cl, Br).

The synthesis, structure, and magnetic behavior of the complexes Cu(qnx)Br(2) (1), Cu(2,3-dmpz)Br(2) (2), Cu(qnx)Cl(2) (3), and Cu(2,3-dmpz)Cl(2) (4) (qnx = quinoxaline, dmpz = dimethylpyrazine) are described. Both X-ray structural data and fitting of the magnetic data suggest that the compounds are well-described as strong-rung, two-leg magnetic ladders with J(rung) ranging from -30 K to -37 K, and J(rail) ranging from -14 K to -24 K. An unexpected decrease in the exchange constant for J(rail) (through the diazine ligand) is observed when the halide ion is changed from bromide to chloride, along with a small decrease in the magnetic exchange through the halide ion. Theoretical calculations on 2 and 4 via a first-principles bottom-up approach confirmed the description of the complexes as two-leg magnetic ladders. Furthermore, the calculations provide an explanation for the experimentally observed change in the value of the magnetic exchange through the dmpz ligand when the halide ion is changed from bromide to chloride, and for the very small change observed in the exchange through the different halide ions themselves via a combination of changes in geometry, bond lengths, and anion volume.

Copper(II) complexes of 2-halo-3-methylpyridine: synthesis, structure, and magnetic behaviour of Cu(2-X-3-CH(3)py)2X'2 [X, X' = chlorine or bromine; py = pyridine].

An isocoordinate family of compounds has been generated with the general formula (2-X-3-methylpyridine)(2)CuX'(2), where X, X' = Cl or Br. While each forms trans-ligand compounds, they vary in copper coordination geometry, canting of the pyridine rings and magnetic behavior. The copper bromide analogues exhibit weak ferromagnetic interactions whereas the copper chloride analogues exhibit antiferromagnetic interactions. Each compound has been characterized by IR, powder X-ray diffraction, single-crystal X-ray diffraction, and temperature dependent magnetic susceptibility.

Synthesis, structure, and magnetic properties of bis(monosubstituted-pyrazine)dihalocopper(II).

The investigation into synthesizing new metal organic compounds with the general formula Cu(S-pyrazine)X(2) using monosubstituted pyrazines has led to the generation of a new family of compounds Cu(S-pyrazine)(2)X(2) with similar structure and magnetic properties. The bis(S-pyrazine)dihalocopper(II) compounds [where S = Cl, CN, OCH(3), and OCH(2)CH(3) and halide = Cl or Br] have been characterized by IR, powder X-ray diffraction, single-crystal X-ray diffraction, and temperature dependent magnetic susceptibility. The bis(chloropyrazine)dihalocopper(II) compounds crystallize in the monoclinic space group P2(1)/n while the methoxy and ethoxy analogues crystallize in the triclinic space group P1. This structurally related family of compounds exhibit antiferromagnetic interactions with exchange constants of approximately -25 K for the chloride analogues and -50 K for the bromide analogues.

catena-Poly[[silver(I)-µ-4-aminopyridine] perchlorate]: a 1-D staircase coordination polymer.

Reaction of 4-amino-pyridine with silver(I) perchlorate leads to a one-dimensional coordination polymer, {[Ag(C(5)H(6)N(2))]ClO(4)}(n), in which the amino-pyridine binds through both N atoms. The perchlorate anion is hydrogen bonded to the amino H atoms and inter-acts weakly with the silver(I) atoms (Ag-O > 2.70 Å), both located on inversion centres, and some aromatic H atoms (O-H > 2.55 ÅA), thereby extending the dimensionality of the assembly. This is the first silver complex in which this ligand acts in a bridging mode.

Synthesis, structure, and magnetic behavior of bis(2-amino-5-fluoropyridinium) tetrachlorocuprate(II).

Reaction of CuCl2 with 2-amino-5-fluoropyridine and HCl in aqueous solution yields bis(2-amino-5-fluoropyridinium) tetrachlorocuprate(II), (5FAP)2CuCl4, (1). The complex crystallizes in the monoclinic space group P21/c with cell dimensions a = 6.926(7) A, b = 21.73(2) A, c = 10.911(10) A, beta = 100.19(2) degrees , V = 1616(3) A3, and R1 = 0.0424 based on 2640 independent reflections. The crystal packing shows that each tetrachlorocuprate ion has four nearest-neighbor Cu(II) ions through three types of Cu-Cl...Cl-Cu potential magnetic interactions: one short Cl...Cl distance (d1 = 3.657 A) and two longer Cl...Cl distances (d2 = 4.073 A) that form a layered distorted honeycomb structure. The third nearest neighbor (d3 = 4.239 A) links these layers into a three-dimensional structure. Both powder and single-crystal magnetic susceptibility measurements on 1, over the temperature range of 1.8-325 K, show significant antiferromagnetic interactions. Attempts to analyze the data using a variety of models showed a best fit to the strong-rung ladder model, with 2Jrung = -17.170(14) and 2Jrail = -5.94(5) K [-11.92(1) and -4.13(3) cm(-1), respectively] for the powder, although a comparable result is obtained using an alternate chain model. However, neither of these two models is compatible with a layered distorted honeycomb crystal packing structure. A first-principles bottom-up theoretical study using the 165 K crystallographic data reproduces the macroscopic properties and reveals that at low temperature the crystal has a 3D magnetic topology (all three magnetic pathways are significant) and a singlet ground state.