The structure of N-meso-(6,8,8,14,16,16-hexamethyl-1,5,9,13-tetraazacyclohexadeca-5,13-diene)nickel(II) chloro(isothiocyanato)zincate(II)

A yellow compound which was crystallised from a solution of (6,8,8,14,16,16-hexamethyl-1,5,9,13-tetraazacyclohexadeca-5,13-diene)bis(isothiocyanato)nickel(II) in aqueous zinc(II) chloride has cations with singlet ground state nickel(II) in square-planar coordination by the nitrogen atoms of the macrocycle. The asymmetric unit has two similar cations. The N₄ group of one cation is near coplanar (r.m.s. displacements ±0.009(1) Å, with Ni displaced by 0.048(1) Å from this plane) while the other cation has significant tetrahedral twisting of the N₄ group (r.m.s. displacements of N atoms ±0.126(2) Å, with Ni displaced by 0.027(2) Å from this plane). The mean Ni–N distances are Ni–N_amine = 1.950(6) and Ni–N_imine = 1.897(6) Å. Both cations have N-meso configurations with saddle conformations, with the substituted chelate rings in boat conformations tilted to one side of the NiN₄ ‘plane’ and the unsubstituted chelate rings tilted to the other side, one in a boat conformation and the other with the central methylene group disordered, the components forming boat {s.o.f. 0.70(1) and 0.74(1) for the two cations} and chair conformation chelate rings. The counter-ions have tetrahedrally coordinated zinc(II) ions, one as [ZnCl₂(NCS)₂]²⁻ ions and the other with one ligand site with disordered Cl⁻ {s.o.f. 0.78(1)} and NCS⁻ ligands, i.e. with disordered [ZnCl₂(NCS)₂]²⁻ and [ZnCl(NCS)₃]²⁻ ions, with an overall composition of [Ni(trans-Me₆[16]diene)][ZnCl_1.9(NCS)_2.1].     

Nickel(II) compounds of a tri-amine mono-imine macrocycle: Preparations and structures of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II) compounds

Reduction of one imine function of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)nickel(II) with 1 molar proportion of NaBH₄ produces as the major product the tri-amine-mono-imine macrocyclic cation (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II), Ni(tm)]²⁺. Pairs of isomeric singlet ground state perchlorate and tetrachlorozincate salts of [Ni(tm)]²⁺ were prepared and the structures determined for the 1RS,8SR,11SR,12RS (labeled as β) and 1RS,8RS,11RS,12SR (labeled as α) tetrachlorozincate salts. Triplet ground state trans-β-[Ni(tm)(NCS)₂] and catena-trans-{β-Ni(tm)-NC-Ni(CN)₂-CN-}_n·2nH₂O have the macrocycle in planar coordination and α-[{Ni(tm)}₂(C₂O₄)](ClO₄)₂ has the macrocycle folded. With pentane-2,4-dione the compounds [β-Ni(tm)]·[α-Ni(tm)(acac)](ClO₄)₃ and [Ni(teta)]·[α-Ni(tm)(acac)](ClO₄)₃ (teta = C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with both square-planar and octahedral Ni(II) cations were prepared and the latter was structurally characterized. Isomerisation in solution of metastable α-[Ni(tm)]²⁺ to stable β-[Ni(tm)]²⁺ is extremely slow, even in base.     

Synthesis and solid-state spectroscopic investigation of some novel diorganotin(IV) complexes of tetraazamacrocyclic ligands

The tetradendate macrocyclic ligands, [H₂L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H₂L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R₂Sn(L-1)/R₂Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R₂SnCl₂ (R = Me or Ph) or n-Bu₂SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state ¹³C NMR, ^119mSn Mössbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO₂ confirmed by XRD analysis.     

Template Syntheses Involving the Carbon Acid Nitroethane. Synthesis and Characterization of Copper(II) Complexes of a 16-membered Tetraaza Macrocycle

New square-planar Cu(II) complexes of 3,11-dimethyl-3,11-dinitro-1,5,9,13-tetraazacyclohexadecane and 1,11-diamino-6-methyl-6-nitro-4,8-diazaundecane cations have been prepared from the one-pot template condensation of [Cu(pn)₂]²⁺ (pn=1,3-diaminopropane) in MeOH with CH₂O and EtNO₂ in the presence of a noncoordinating base. Reduction of the nitro group in the (3,11-dimethyl-3,11-dinitro-1,5,9,13-tetraazacyclohexadecane)copper(II) cation, may be achieved by Zn/acid reduction. The Cu(II) complex of the reduced form of the ligand, namely (3,11-diammonio-3,11-dimethyl-1,5,9,13-tetraazacyclohexadecane)copper(II), has also characterized. With the macrocyclic ligand, rac and meso isomers have been identified, the meso form being the major product. Elemental analyses, i.r. and u.v.–vis. spectroscopy, f.a.b. mass spectra conductometric, magnetic measurements and cyclic voltammetry have been used to characterize the complexes.     

Synthesis,Crystal Structure and Spectroscopic Properties of [2,13‐Bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,01.18,07.12)docosane]copper(II) Diperchlorate Acetonitrile Disolvate

The N‐functionalized macrocyclic ligand 2,13‐bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,0^1.18,0^7.12)docosane (L³) and its copper(II) complex were prepared. The crystal structure of [Cu(L³)](ClO₄)₂·2CH₃CN was determined by single‐crystal X‐ray diffraction at 150 K. The copper atom, which lies on an inversion centre, has a square planar arrangement and the complex adopts a stable trans‐III configuration. The longer distance [2.081(2) Å] for Cu–N(tertiary) compared to 2.030(3) Å for Cu–N(secondary) may be due to the steric effect of the attached naphthalenylmethyl group on the tertiary nitrogen atom. Two perchlorate ions are weakly attached to copper in axial sites and are further connected to the ligand of the cation through NH ··· O hydrogen bonds [N ··· O 3.098 Å]. IR and UV/Vis spectroscopic properties are also described.     

Copper(II), nickel(II) and cobalt(III) complexes of the macrocyclic ligand C-meso-7,14-diphenyl-5,6-butano-12,13-butano-1,4,8,11-tetraazacyclotetradeca-4,11-diene

Summary Metal complexes of the macrocyclic tetraaza ligand C-meso-7,14-diphenyl-5,6-butano-12,13-butano-1,4,8,11-tetraazacyclotetradeca-4,11-diene (L) are described. The copper(II) and nickel(II) complexes, isolated as their perchlorate salts, are 4-coordinate species. Several cobalt(III) complexes,trans-[CoLX₂]⁺(X = Cl^–, Br^–, NO ₂ ^– or N ₃ ^– have also been characterised. The most probable stereochemistry of the ligand in the metal complexes is the C-meso-N-meso arrangements of the chiral centres. The N-meso stereochemistry leads to the bulky phenyl groups lying in equatorial positions. I.r. and d-d spectra are reported for the various complexes described.     

Conformational study of Co(II), Ni(II), and Cr(III) complexes of the edta-type: Crystal structure of 1D polymeric trans(O)-Ba[Co(1,3-pddadp)] · 8H2O complex stabilized by infinite water tapes

The trans(O⁶) isomer of the Ba[Co(1,3-pddadp)] · 8H₂O complex (where 1,3-pddadp represents hexadentate 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion) has been prepared and characterized by X-ray crystallography. In the crystal structure the complex cations and anions are bridged by carboxylate oxygen atoms from the in-plane coordinated glycinate rings (G-rings) of [Co(1,3-pddadp)]²⁻ and by the barium-coordinated water molecules, thus forming 1D polymeric chains, separated by infinite water tapes hydrogen bonded to the [Co(1,3-pddadp)]²⁻ carboxylate oxygens from the out-of-plane β-alaninate rings (R-rings). Conformational analysis of the three possible geometrical isomers: trans(O⁵), trans(O⁵O⁶), and trans(O⁶) of the [Co(1,3-pddadp)]²⁻ complex, with ligand acting as hexadentate, as well as of the corresponding complexes of Ni(II) and Cr(III) has been performed using the consistent force field (CFF) method, with the parameters developed previously for edta-type complexes of chromium(III) and supplemented with new parameters for cobalt(II) and nickel(II). The energy-minimized structure of the trans(O⁵O⁶) isomer represents the global minimum for the [M(1,3-pddadp)]ⁿ⁻ (M = Co(II), Ni(II), and Cr(III)) species. The occurrence of the least energetically favored trans(O⁶) isomer in a crystal and the exceptional conformation of the axially oriented β-alaninate rings can be accounted for by the stabilizing role of the infinite tapes of planar cyclic water pentamers and hexamers which act as a “glue” to reinforce the coordination polymeric chains.     

Gas-phase CT-stabilized Ag(I) and Zn(II) metal-organic complexes - Experimental versus theoretical study

A series of 14 new metal-organic compounds of Ag(I) and Zn(II), i.e. trichloro(1-(2-hydroxyethyl)piperazinium)zinc(II) (1), 1-[2-(2-hydroxyethoxy)-ethyl]-piperazinium tetrachlorozincate(II) (2), tetrachlorozincate(II) salt of 4-(2-aminoethyl)morpholine (3), 1,4-bis(2-hydroxyethyl)piperazinium tetrachlorozincate(II) (4), 5-sulfosalicylate coordination polymer of Ag(I) (5) [3dd], mandelate coordination polymer of Ag(I) (6) [1r], hexa-aqua zinc(II) 5-sulfosalicylate monohydrate (7), cyclic quaternary N-ethylmorpholine tetrachlorozincate(II) monohydrate (8), 2,2′:6′,2″-terpyridinium tetrachlorozincate(II) (9), bis(guaninium) tetrachlorozincate(II) dihydrate (10), bis(8-hydroxyquinolinium) tetrachlorozincate(II) (11), zinc(II) complexes of 2,4-dihydroxy-(12) and 2,3-dihydroxy-(13) benzoic acid, silver(I) complex of 2,4-dihydroxybenzoic acid (14), as well as cyclic quaternary N-ethylmorpholine chloride monohydrate (8a), are synthesized, isolated spectroscopic and structurally characterized by the mass spectrometry, electronic absorption and vibrational spectroscopy, diffuse reflectance and fluorescence spectroscopy in condense phases, single crystal X-ray diffraction, ICP and thermal methods. Quantum chemical DFT calculations, including NBO analysis are performed for all of the obtained complexes, their ligands as well as series of structurally related model metal-organic chromophores. The obtained correlation dependences between the theoretical and experimental structural and spectroscopic data both in gas- and condense phases, underlying an explanation of the experimentally observed mass spectrometrically stable metal-organic species in the gas phase as well as the atypical CT bands in excited state.     

Synthesis and structures of (13-hydroxylamino-5,7,7,13-tetramethyl-1,4,8,11-tetraazacyclotetradec-4-ene-κ)nickel(II) tetrachlorozincate(II) and (13-azonium-5,5,7,13-tetramethyl-1,4,8,11-tetraazacyclotetradecane-κ)nickel(II) tetrachlorozincate(II) chloride 2.25 water

Zinc/acid reduction of the nitro function of (5,7,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II) yields (13-hydroxylamino-5,7,7,13-tetramethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II), isolated as the tetrachlorozincate salt, for which the structure is reported. This has singlet ground state nickel(II) in square-planar coordination by the three amine and the imine nitrogen atoms of the macrocycle. There is no interaction between the nickel(II) ion and the axially oriented hydroxylamino group.Zinc/acid reduction of the nitro function of (5,5,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradecane)nickel(II) yields (13-amino-5,5,7,13-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II), isolated from acid solution as (13-azonium-5,5,7,13-tetramethyl-1,4,8,11-tetraazacyclotetradecane-κ⁴)nickel(II) tetrachlorozincate(II) chloride 2.25 water, for which the structure is reported. The two independent cations have singlet ground state nickel(II) in square-planar coordination by the four secondary amine nitrogen atoms of the macrocycle, with the protonated amine substituent axially oriented.The cations of both compounds show disorder in the location of the axial methyl component of the gem-dimethyl group, manifest as reversal of the trimethyl substituted 1,3-amine-imine or 1,3-diamine chelate rings, arising from co-crystallisation of enantiomers.     

Structure and redox behavior of Ru(II)-diene complexes

A series of Ru(acac)₂(η⁴-diene) complexes containing cis- and trans-diene coordination have been investigated by cyclic voltammetry to correlate structural bonding and conformation patterns of diene ligands with redox behaviors. The solid-state structure of Ru(acac)₂(2,3-dimethyl-1,3-butadiene) has been determined by single crystal X-ray diffraction methods. Ru(acac)₂(2,3-dimethyl-1,3-butadiene) crystallizes in the monoclinic space group C2/c with a = 12.368(2) Å, b = 17.0600(2) Å, c = 16.0110(2) Å, β = 98.4405(10)° and V = 3341.38(10) ų for Z = 8. A structural comparison between several Ru-trans-η⁴-diene complexes and Ru-η⁴-1,3-cyclohexadiene revealed no difference in the Ru-C(diene) bond distances. However, through cyclic voltammetry experiments these species demonstrated different redox behavior, as function of the coordinated diene ligand.     

Synthesis,structures, electrochemistry and catalytic activities of copper(II) and palladium(II) complexes with asymmetric tetraazacycloannulenes

Copper(II) and palladium(II) complexes with 15-membered asymmetric 5,9-dihydro-2,4,10,12-tetramethyl-1,5,9,13-monobenzotetraazacyclo[15]tetradecine have been synthesized and characterized. The electrochemical behaviors of the complexes showed a reduction and two one-electron irreversible oxidation waves in given potential ranges due to the metal ion and macrocycle ring, respectively. The electrocatalytic reduction of dioxygen on glassy carbon electrodes electropolymerized by such 15-membered and 14-membered tetraazaannulene complexes occurred at 160–280 mV (versus SCE), less negative than on the bared one at pH 7.0. The catalytic activities of the copper(II) complexes in the oxidation of p-Xstyrene (X = OCH₃, CH₃, H, F, Cl) were higher than those of the palladium(II) ones. The structures of the 15-membered copper(II) and palladium(II) complexes were determined using the X-ray diffraction method.     

Physicochemical Insight into Coordination Systems Obtained from Copper(II) Bromoacetate and 1,10-Phenanthroline

Two different coordination compounds of copper were synthesized from the same building blocks (1,10-phenanthroline, bromoacetate anions, and copper cations). The synthesis parameters were carefully designed and evaluated to allow the change of the resulting compounds molecular structure, i.e., formation of mononuclear (bromoacetato-O,O’)(bromoacetato-O)aqua(1,10-phenanthroline-N,N’)copper(II) and dinuclear (μ-bromido-1:2κ²)bis(μ-bromoacetato-1κO,2κO’)bis(1,10-phenanthroline-N,N’)dicopper(II) bromoacetate bromoacetic acid solvate. The crystal, molecular and supramolecular structures of the studied compounds were determined and evaluated in Hirshfeld analysis. The UV-Vis-IR absorption and thermal properties were studied and discussed. For the explicit determination of the influence of compounds structure on radiation absorption in UV-Vis range, density functional theory and time-dependent density functional theory calculations were performed.     

Synthesis and properties of nickel(II) and copper(II) complexes of a di-N-acetamide tetraaza macrocycle

The syntheses of the hexadentate ligand 2,13-bis(acetamido)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane (L²) and its complexes with Ni(II) and Cu(II) are described. Crystal structures of H₂L²·2HClO₄ (1), [Ni(L²)](ClO₄)₂ (2) and [Cu(L²)](ClO₄)₂ (3) are reported. The two pendant acetamide groups of the macrocyclic ligand 1 are trans to each other and the absolute configuration is a trans-IV in the solid state. The crystal structures of 2 and 3 revealed an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two oxygen atoms of the pendant acetamide groups at the axial positions. The nickel(II) and copper(II) ions are located at an inversion center. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the presence of the pendant arms.     

Synthesis and structures of nickel(II) and copper(II) compounds of 5,5,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradecane and the 13-ethyl-5,5,7-trimethyl-homologue

Reduction by NaBH₄ of the imine functions of (5,7,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradec-4-ene)-nickel(II) and -copper(II), and of their 13-ethyl-5,7,7-trimethyl-homologues, yield the nitro-substituted cyclic tetraamine cations (5,5,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradecane)-nickel(II) and -copper(II), [M(neh)]²⁺, and (13-ethyl-5,5,7-trimethyl-homologues, [M(nph)]²⁺, respectively. The nickel(II) cations form square–planar, singlet ground, state salts with poorly coordinating anions and octahedral, triplet ground state, compounds with additional ligands, trans-β-[Ni(neh)A₂], A⁻ = Cl⁻, NCS⁻ and trans-β-[Ni(neh)A₂](ClO₄)₂, X = NH₃, MeCN, all with nitrogen configuration III, 1R,4R,8S,11S = β. With oxalate the chain-polymeric compound catena-trans-β-[Ni(neh)(μ-C₂O₄)]_n · 3n(H₂O) is formed. Folded macrocycle compounds cis-α-[Ni(neh)(C₅H₇O₂)]ClO₄ and cis-α-[{Ni(neh)}₂(C₂O₄)](ClO₄)₂ are formed with the chelates acetylacetonate and oxalate, with configuration 1R,4R,8R,11R = α. These react with HClO₄ to form metastable α-[Ni(neh)](ClO₄)₂ with retention of configuration. The copper(II) cations form crimson salts with poorly coordinating anions and compounds of the type β-[Cu(neh)A]ClO₄ of varying shades of blue with coordinating anions. Structures of singlet ground state square–planar nickel(II) compounds β-[Ni(neh)](ClO₄)₂ · H₂O, β-[Ni(neh)](ClO₄)₂, β-[Ni(neh)]₂[ZnCl₃(OH₂)]₂[ZnCl₄] · H₂O and α-[Ni(neh)](ClO₄)₂, the triplet ground state chain-polymeric compound catena-trans-β-[Ni(neh)(μ-C₂O₄)]_n · 3n(H₂O) and of square–pyramidal β-[Cu(nph)Cl]ClO₄ are reported.     

A new molecular building blocks: Synthesis,crystal structure,magnetic and spectroscopic properties of Cu(II) and Ni(II) macrocyclic complexes

New higly unsaturated macrocyclic building blocks [CuLSCN]·ClO₄ (1) (L = N-dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) and [NiL(SCN)₂] (2) (L = N-dl-5,12-dimethyl-7,14-diisopropyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) were synthesized and the crystal structures of both compounds were determined. Both complexes crystallizes in monoclinic, space group P2₁/n (1) and P2₁/c (2). Their magnetic properties were studied over the temperature range 1.8–300 K using a Quantum Design SQUID magnetometer (MPMSXL-5-type). The results indicate that both compounds behave as weakly interacting paramagnetic centers in the crystal lattice. The effects of hydrogen bond mediating the magnetic exchange interactions on the spin density have been evidenced by DFT calculations. The NIR–Vis–UV diffuse-reflectance electronic spectra confirm the square pyramidal and octahedral geometry around Cu²⁺ and Ni²⁺ metal ions.     

"Swollen" Macrocycles: Palladium(II)-Directed Template Syntheses of Pendant-Arm 14-, 16-, and 18-Membered Macrocycles

The bis(diamine)palladium(II) cations (diamine = ethane-1,2-diamine, propane-1,3-diamine, or butane-1,4-diamine) all undergo condensation reactions with formaldehyde and nitroethane to produce macromonocycles where each pair of cis-disposed primary amines has been converted to a -NH-CH(2)-C(CH(3))(NO(2))-CH(2)-NH- strap. The 14-membered-ring macrocycle has been previously prepared by condensation around copper(II) and nickel(II), but this does not permit synthesis of the larger ring macrocycles. The macrocyclic complex (6,13-dimethyl-6, 13-dinitro-1,4,8,11-tetraazacyclotetradecane)palladium(II) perchlorate crystallizes in the triclinic space group P&onemacr;, a = 8.105(3) ?, b = 8.370(2) ?, c = 9.437(4) ?, alpha = 69.04(3) degrees, beta = 68.60(3), gamma = 71.53(3) degrees. Complexes of the 16- and 18-membered macrocycles (3,11-dimethyl-3,11-dinitro-1,5,9,13-tetraazacyclohexadecane)palladium(II) perchlorate and (3,12-dimethyl-3,12-dinitro-1,5,10,14-tetraaazacyclooctadecane)palladium(II) perchlorate crystallize in the monoclinic space group P2(1)/c, with a = 8.391(2) ?, b = 12.816(3) ?, c = 23.925(9) ?, and beta = 93.18(2) degrees, and the triclinic space group P&onemacr;, with a = 7.746(5) ?, b = 9.912(5) ?, c = 18.96(2) ?, alpha = 91.76(6) degrees, beta = 101.73(7) degrees, and gamma = 112.83(5) degrees respectively. The larger macrocycles are "swollen" by incorporating longer methylene chains, "swelling" leading to an increase in Pd-N distance and in tetrahedral distortion, with the dominant geometric isomer apparently changing with macrocycle size from anti-disposed nitro pendants (14-membered) to the syn isomer (16-, 18-membered). An irreversible Pd(II/IV) oxidation occurs at ca +1 V (vs Ag/AgCl), varying slightly with ring size, with a multi-electron nitro group reduction observed near -0.8 V in each case. Electronic spectra also vary slightly with ring size.     

Copper(II) and nickel(II) complexes of a neutral pentadentate Schiff base

A new pentadentate Schiff base 2,6,10-triaza-1,11-bis(2′-aminophenyl)-undeca-1,10-diene, abaDPT, and its complexes of general formula M(abaDPT)X₂ where M = Cu(II), Ni(II), X = Cl, Br, I, NO₃ and ClO₄, have been prepared. The complexes have been characterized by electronic and IR spectra, EPR, magnetic moments, molar conductances, and elemental analysis. IR data show an interaction between halide anion of the outer coordination sphere and the complexed amino group. EPR and spectrophotometric data of most of the copper compounds are consistent with a distorted square pyramidal geometry. Single crystal EPR studies of Cu(abaDPT)(NO₃)₂ and Cu(abaDPT)Br₂ revealed that copper atoms in the former compound occupy two magnetically inequivalent places in the lattice while copper atoms in the latter compound take identical sites. Principal g tensor axes of the two compounds have been determined.     

Uncommon isonicotinamide supramolecular synthons in copper(II) complexes directed by nitrate and perchlorate anions

The title compounds, trans‐diaquabis(nitrato‐κO)bis(pyridine‐4‐carboxamide‐κN¹)copper(II), [Cu(NO₃)₂(C₆H₆N₂O)₂(H₂O)₂], (I), and trans‐diaquatetrakis(pyridine‐4‐carboxamide‐κN¹)copper(II) bis(perchlorate), [Cu(C₆H₆N₂O)₄(H₂O)₂](ClO₄)₂, (II), are composed of mononuclear coordination entities involving Cu^II ions and isonicotinamide. In (I), the centrosymmetric tetragonally distorted octahedral copper(II) environment contains trans‐related isonicotinamide and water molecules in the equatorial plane and two nitrate ions occupying the axial sites. In (II), the equatorial plane of the C₂‐symmetric distorted octahedron is built up of four isonicotinamide ligands, while water molecules occupy the axial positions. The complex molecules of (I) and (II) are linked into three‐dimensional supramolecular frameworks by O—H...O and N—H...O hydrogen bonds. The nitrate and perchlorate ions are building blocks that disturb the robust R₂²(8) amide supramolecular motif commonly found in crystal structures of copper–isonicotinamide complexes.     

Reactions of urocanic acid (UCA) methyl esters with singlet oxygen and 4-methyl-1,2,4-triazoline-3,5-dione (MTAD)

Singlet oxygen adds to the imidazole ring of cis- and trans-methyl urocanate (MUC) to yield the corresponding 2,5-endoperoxides, which are modestly stable at low temperature but decompose upon warming to form complex reaction mixtures. MTAD, a singlet oxygen mimic, reacts with cis- and trans-MUC to yield stereospecific [4+2] reaction products involving the olefinic side chain and the C₄-C₅ double bond of the imidazole ring. trans-MUC forms a 1:2 MTAD adduct while the cis isomer yields only the 1:1 adduct at 25 °C. The stereospecificity and absence of MeOH trapping adducts indicate that these reactions may not involve open or trappable dipolar intermediates.