The monofunctionalized 1,4,7-triazacyclononane derivatives 1,4,7-triazacyclononane-N-acetate (L) and N-(2-hydroxybenzyl-1,4,7-triazacyclononane (HL) and their complexes with vanadium(IV)/(V). Localized and delocalized electronic structures in compounds containing the mixed valent [OV---O---VO] core

The synthesis of the tetradentate pendant arm macrocycles 1,4,7-triazacyclononane-N-acetate (L¹) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL²) and their coordination chemistry with vanadium(IV) and (V) are reported. The following mononuclear species have been prepared and characterized by UV-Vis, IR spectroscopy: [L¹V^IVO(NCS)] (1), [L¹VO₂]·H₂O (2), [L²VO(NCS)] (3), [L²VO(NCS)]Cl (4), and [L²VO₂] (5). In addition, the dinuclear, mixed valent complexes [L₂¹V₂O₃]Br (6), [L₂²V₂O₃](ClO₄)·0.5acetone (7), and the homovalent complex [L₂²V₂O₃](ClO₄)₂ (8) have been synthesized. Complexes 2, 3, 6 and 7 have been characterized by single crystal X-ray crystallography. Crystal data: 2, space group P2₁c,a=9.944(4),b=6.701(3),c=18.207(8)Å, β=102.88(3)°, V=1182.7 ų, Z=4, D_calc=1.51 g cm⁻³, R=0.049 based on 4760 reflections; 3, space group Pbca, A=11.003(6), b=14.295(7), C=20.21(1) Å, V=3178.8 ų, Z=8, D_calc=1,50 g cm⁻³, R=0.057 based on 1049 reflections; 6, space Pbcn, a=12.922(3), B=13.852(3), C=12.739(3) Å, V=2280.3 ų, Z=4, D_calc=1,75 g cm⁻³, R=0.047 based on 1172 reflections; 7, space group C2/c, A=23.553(9), B=13.497(5), C=20.951(8) Å, β=90.03(3)°, V=6660.2 ų, Z=8, D_calc=1.49 g cm⁻³, R=0.053 based on 3698 reflections. Complexes 6 and 7 are mixed valent V(IV)/(V) complexes containing the [OV---O---VO]³⁺ core. In the solid state 6 belongs to class III (delocalized) and 7 to class I (localized) according to the Robin and Day classification of mixed valent compounds. A rationale for these differing electronic structures is given.     

Synthesis and characterization of 1:2 metal complexes of the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) and the X-ray structure of [CuL2](PF6)

The first 1:2 metal complexes of 2-(2′-pyridyl)quinoxaline (L) have been isolated. The physical and spectroscopic characteristics of the compounds [MCl₂L₂] (M = Ni, Cu, Cd) and [Cu^IL₂](PF₆) are described. The structure of the copper(I) complex has been determined by X-ray diffraction methods. Crystals are orthorhombic, space group P_cnb with A = 11.014(2), B = 12.886(2), C = 17.806(4) Å, V = 2527.1(9) ų and Z = 4. Refinement of the structure gave a final R factor of 0.046 (R_w = 0.041) for 814 unique reflections having I > 2.0σ(I). The ligand L acts as a bidentate chelate, the ligated atoms being the pyridine nitrogen and the nearest quinoxaline nitrogen. The structure of [CuL₂]⁺ consists of a distorted tetrahedral arrangement around the copper(I) atom with Cu---N bond lengths of 2.023(6) and 2.059(5) Å and the N---Cu---N angle of the chelating ligand equal to 80.6(2)°. A monomeric trans pseudo-octahedral stereochemistry is assigned for the [MCl₂L₂] complexes.     

Iron(III), nickel(II) and cadmium(II) complexes of triazamacrocyclic ligand with pendant nitrile groups 1,4,7-tris(cyanomethyl)-1,4,7-triazacyclononane: Synthesis, structural characteristics and artificial nuclease activity

Three novel transition metal complexes with 1,4,7-tris(cyanomethyl)-1,4,7-triazacyclononane (L) were synthesized and structurally characterized. In complex [FeLCl₃]·2H₂O (1), three N-donors from the macrocyclic backbone and three chloride anions complete the coordination polyhedron around Fe(III) and lead to a neutral [FeLCl₃] unit. The neutral Fe(III) units of the same chirality are linked through weak interactions into 3D supramolecular network with hexagonal channels. Guest water molecules trapped inside the channel are associated into an unprecedented 1D linear chain. The crystal structures of complexes [NiL(CH₃CN)₃](ClO₄)₂·0.5H₂O (2) and [CdL(CH₃CN)₃](ClO₄)₂·0.5H₂O (3) reveal that the metal center lies in a distorted octahedral N6 environment with three acetonitrile occupying the remaining coordination sites opposite to the macrocyclic ring. The artificial nuclease activity of redox-active complex 1 towards pMD-AMT plasmid DNA was assessed by gel electrophoresis. As a result, complex 1 can effectively cleave supercoiled DNA under near physiological conditions with/without H₂O₂ in a time- and complex concentration-dependent manner.     

Cis- and trans-titanium complexes with doubly silyl-bridged dicyclopentadienyl ligands: molecular structure of [(TiCl)2(μ-O){(SiMe2)2(η-C5H3)2}]2(μ-O)2

The reaction of TiCl₄ with Li₂[(SiMe₂)₂(η⁵-C₅H₃)₂] in toluene at room temperature afforded a mixture of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] in a molar ratio of 1/2 after recrystallization. The complex trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] was hydrolyzed immediately by the addition of water to THF solutions to give trans-[(TiCl₂)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] as a solid insoluble in all organic solvents, whereas hydrolysis of cis-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] under different conditions led to the dinuclear μ-oxo complex cis-[(TiCl₂)₂)(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] and two oxo complexes of the same stoichiometry [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ as crystalline solids. Alkylation of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] with MgCIMe led respectively to the partially alkylated cis-[(TiMe₂Cl)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] and the totally alkylated trans-[(TiMe₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] compounds. The crystal and molecular structure of the tetranuclear oxo complex [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ was determined by X-ray diffraction.     

Charge-transfer complexes of benzylviologen (1,1′-dibenzyl-4,4′-bipyridinium(2+) cation) with cyanocuprate(I) and the structure of (BzV)3Cu9(CN)15·H2O

Reactions between 1,1′-dibenzyl-4,4′-bipyridinium(2+) (benzylviologen, BzV) chloride and cyanocuprates(I) gave two charge-transfer complexes having different colors: dark brown (BzV)₃Cu₉(CN)₁₅·H₂O and light brown (BzV)Cu(CN)₃·2H₂O. An X-ray crystal analysis of the former compound showed that nine crystallographically nonequivalent Cu atoms form three kinds of triad ---Cu---(CN)---Cu--- screws, which are linked by CN groups resulting in a unique three-dimensional network structure. Three of the nine Cu atoms have distorted tetrahedral (td) coordination geometries while the others have triangular plane (tp) geometries. Each screw consists of a (-tp-td-tp-)_n array. There are three crystallographically nonequivalent viologen molecules. Certain CuCN moieties are located above a viologen ring or by the side of a viologen ring, with close interatomic contacts. These close contacts are characteristic of the charge-transfer complex and are responsible for the deep color of the complex.     

Synthesis, solution behaviour and molecular structures of 16-electron closo-2-(Ph3P)-1-N,2-[μ-(η-CH2CH=Ch2)]-1-N-(σ-CH2CH=CH2)-2,1- RhCB10H10, the first η-olefinic monocarbon metallacarborane

The first η²-olefinic monocarbon metallacarbone closo-2-(Ph₃P)-1-N,2-[μ-(η²-CH₂CH=Ch₂)]-1-N-(σ-CH₂CH=CH₂)-2,1- RhCB₁₀H₁₀ has been prepared by the reaction of the dimeric anion {[Ph₃PRhB₁₀H₁₀CNH₂]₂-μ-H}⁻[PPN]⁺ with allyl bromide and characterized by a combination of spectroscopic methods and a single-crystal X-ray diffraction study. The variable temperature ¹H and ¹³C NMR studies revealed the fluxional behavior of the η²-olefinic complex in CD₂Cl₂ solution which is associated with the allyl side-chain exchange process.     

Copper(II) complexes with (2-hydroxybenzyl-2-pyridylmethyl)amine–Hbpa: syntheses, characterization and crystal structures of the ligand and [Cu(II)(Hbpa)2](ClO4)2·2H2O

Copper(II) complexes were synthesized and characterized by means of elemental analysis, IR and visible spectroscopies, EPR and electrochemistry, as well as X-ray structure crystallography. The group consists of discrete mononuclear units with the general formula [Cu(II)(Hbpa)₂](A)₂·nH₂O, where Hbpa=(2-hydroxybenzyl-2-pyridylmethyl)amine and A=ClO₄ ⁻, n=2 (1), CH₃COO⁻, n=3 (2), NO₃ ⁻, n=2 (3) and SO₄ ²⁻, n=3 (4). The structures of the ligand Hbpa and complex 1 have been determined by X-ray crystallography. Complexes 1–4 have had their UV–Vis spectra measured in both MeCN and DMF. It was observed that the compounds interact with basic solvents, such that molecules coordinate to the metal in axial positions in which phenol oxygen atoms are coordinated in the protonated forms. The values were all less than 1000 M⁻¹ cm⁻¹. EPR measurements on powdered samples of 1–3 gave g/A values between 105 and 135 cm⁻¹, typical for square planar coordination environments. Complex 4·3H₂O exhibits a behaviour typical for tetrahedral coordination. The electrochemical behaviour for complexes 1 and 2 was studied showing irreversible redox waves for both compounds.     

Catalytic and electrochemical properties of new manganese(III) compounds of 2-(2′-hydroxyphenyl)-oxazoline (Hphox or HClphox). Molecular structures of [Mn(Clphox)2(MeOH)2](ClO4) and [Mn(phox)2(MeOH)2][Mn(phox)2(ClO4)2](H2O)2

New manganese(III) complexes of Hphox (2-(2′-hydroxyphenyl)-oxazoline) and HClphox (2-(5′-chloro-2′-hydroxyphenyl)-oxazoline) have been synthesised. The X-ray structures of [Mn(phox)₂(MeOH)₂][Mn(phox)₂(ClO₄)₂](H₂O)₂ and [Mn(Clphox)₂(MeOH)₂](ClO₄) show the manganese(III) ions to be octahedrally coordinated with methanol or perchlorate at the axial coordination sites. The cyclic voltammograms of the complexes, with the exception of [Mn(phox)₂(acac)] (Hacac=2,4-pentanedione), show an irreversible reduction wave of manganese(III) to manganese(II). After addition of an excess of 1-methylimidazole (1-Meim), the reduction process shifts towards lower potentials and becomes (quasi-) reversible, indicating that the presence of 1-Meim affects the catalytic efficiency of the complexes. The complexes catalyse the epoxidation of styrene by dihydrogen peroxide. The cumulative turnover numbers towards styrene oxide obtained after 15 min. vary from 16 for [Mn(Clphox)₂(MeOH)₂](ClO₄) to 26 for [Mn(phox)₂(acac)]. Ligand degradation appears to be the limiting factor for obtaining higher turnover numbers.     

CO substitution and diphosphine ligand chelation in the reaction between 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Re(2(CO)8(μ-H)(μ-η,η-C CPh)

The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and the dirhenium compound Re₂(CO)₈(μ-H)(μ-η¹,η²-C CPh) in CH₂Cl₂ at room temperature proceeds by CO loss to give the dirhenium complex Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) (1). This new complex was characterized in solution by IR and NMR (¹H and ³¹P) spectroscopy and in the solid state by X-ray diffraction analysis. Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) crystallizes in the triclinic space group

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γ = 69.240(6)°, V = 2024.9(3) ų, Z = 2, d_calc = 1.862 g cm⁻³ R = 0.0221, R_w = 0.243 for 4066 observed reflections. The bpcd ligand in 1 adopts a chelating mode with a linear phenylacetylide ligand being located on the adjacent rhenium center cis to the bpcd ligand. This complex represents the first structurally characterized example of a hydrido-bridged dirhenium complex possessing both a linear acetylide ligand and a chelating diphosphine ligand.     

X-ray crystal structure of Cu2(medpco-2H)Cl2, (medpco = N,N′-bis(2-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. Copper(II) complexes of a deprotonated binucleating pyridine N-oxide ligand

The X-ray structure is reported for the complex Cu₂(medpco-2H)Cl₂, (medpco = N,N′-bis-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. The complex is triclinic, , a=8.313(4), B=11.403(5), C=11.611(3) Å, =91.66(3), β=108.99(4), γ=109.60(3)° and Z=2. The deprotonated ligand (medpco-2H)²⁻ acts as a binulceating ligand, producing an N-oxide-bridged complex. Each copper in Cu₂(medpco-2H)Cl₂ is five-coordinate, being coordinated by a bridging N-oxide oxygen, a deprotonated amide nitrogen, a tertiary amine nitrogen and two bridging chlorides. The complex does not exhibit significant magnetic interaction, and this may be the result of distortion of the bridging geometry from planarity. A range of other, apparently N-oxide-bridged, complexes of the type Cu₂(medpco-2H)X₂ is reported. The complex Cu₂(medpco-2H)Br₂·H₂O is strongly antiferromagnetic, with magnetic data closely fitting the expected binuclear structure.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Convenient preparation of [CuX(PCy3)2](X = Br, I, SCN, N3) complexes. X-ray crystal structure of [Cu(N3)(PCy3)2] (Cy = cyclo-C6H11)

The labile cations [Cu(F-BF₃)(PCy₃)₂] and [Cu(OTf)(PCy₃)₂] are versatile precursors for the formation of [Cu(X)(PCy₃)₂] (X = Br, I, SCN, N₃) complexes by metathesis with NaX. The azide [Cu(N₃)(PCy₃)₂] is triclinic, space group , a = 9.755(4), B = 22.78(1), C = 9.284(6) Å, = 96.76(3), β = 115.36(3), γ = 94.20(5)°, Z = 2.     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.     

Synthesis and characterization of homologous nickel(II) and palladium(II) complexes with biphosphine monoxide ligands Ph2P(CH2)nP(O)Ph2 (n = 1–3) and pTol2P(CH2)P(O)pTol2

A series of cationic nickel complexes [(η³-methally)Ni(PP(O))]SbF₆ (1–4) [PP(O) = Ph₂P(CH₂)P(O)Ph₂ (dppmO) (1), Ph₂P(CH₂)₂P(O)Ph₂ (dppeO) (2), Ph₂P(CH₂)₃P(O)Ph₂ (dpppO) (3), pTol₂P(CH₂)P(O)pTol₂ (dtolpmO) (4)] has been synthesized in good yields by treatment of [(η³-methally)NiBr]₂ with biphosphine monoxides and AgSbF₆. The ligands are coordinated in a bidentate way. Starting from [(η³-all)PdI]₂ the cationic complexes [(η³-all)PP(O))]Y (8–14). [PP(O) = dppmO, dppeO, dpppO, dtolpmO;Y = BF₄, SbF₆, CF₃SO₃, pTolSO₃] were synthesized in good yields. The coordination mode of the ligand is dependent on the backbone and the anion, revealing a monodentate coordination with dppmO for stronger coordinating anions. The intermediates [(η³-all)Pd(I)(PP(O)-κ¹-P)] (5–7) [PP(O) = dppmO (5), dppeO (6), dtolpmO (7)] were isolated and characterized. Neutral methyl complexes [(Cl)(Me)Pd(PP(O))] (15–18). [PP(O) = dppmO (15), dppeO (16), dpppO (17), dtolpmO (18)] can easily be obtained in high yields starting from [(cod)PdCl₂]. For dppmO two different routes are presented. The structure of [(Me)(Cl)Pd{;Ph₂P(CH₂-P(O)Ph₂-κ²-P,O};] · CH₂Cl₂ (15) with the chlorine atom trans to phosphorus was determined by X-ray diffraction.     

Synthesis and crystal structure of tetranuclear copper(I) and silver(I) complexes bridged by 2-amino-1,3,4-thiadiazole (atdz): [Cu4(atdz)6](ClO4)4·2CH3OH and [Ag4(atdz)6](ClO4)4

Two novel tetracopper(I) and tetrasilver(I) complexes [Cu₄(atdz)₆](ClO₄)₄·2CH₃OH (1) and [Ag₄(atdz)₆](ClO₄)₄ (2), have been prepared using 2-amino-1,3,4-thiadiazole (atdz), and their crystal structures and properties have been determined. On each tetranuclear complex, two Cu or Ag atoms (M) are bridged by two atdz ligands to form a six-membered N₂M₂N₂ framework. The two N₂M₂N₂ frameworks are in parallel linked by another atdz ligand to provide the tetranuclear structure with a rectangular M₄ core. The four Cu or Ag atoms possess a trigonal-square geometry. The two adjacent MM separations are (3.096(1) and 3.412(1) Å) and (3.316(2) and 3.658(2) Å) for 1 and 2, respectively. On both tetranuclear complexes there are two species of hydrogen bonds between the ClO₄ ⁻ anions and the NH₂ group of atdz ligands. It is proposed that the hydrogen bonds are related to the stabilization of the tetranuclear structure during the crystallization process.     

Synthesis, crystal structure and magnetic properties of the chiral iron(II) chain [Fe(bpym)(NCS)2]n (bpym = 2,2′-bipyrimidine)

The iron(II) compound of formula [Fe(bpym)(NCS)₂]_n (bpym = 2,2′-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the tetragonal P4₁ (No. 76) and P4₃ space groups, a = 8.849(2), C=16.486(3) Å, V=1290.9(5) ų, Z=4, D_c=1.699 g cm⁻³, M_r=330.2, F(000)=664, λ(Mo K)=0.71073 Å, μ(Mo K)=14.8 cm⁻¹ and T=295 K. A total of 2449 reflections was collected over the range 3≤2≤55°; of these, 1657 were unique and 1321 were considered as observed (13σ(I)) and used in the structural analysis. The final R and R_w residuals were 0.027 and 0.026, respectively. The structure is made up of chiral (Δ and Λ enantiomers crystallize in the same crop) chains of iron(II) atoms bridged by bis-chelating bpym, the electroneutrality being achieved by N-bonded thiocyanato groups in cis position. Each metal atom is in a distorted FeN₆ octahedral environment, the Fe---N bonds ranging from 2.265(3) to 2.028(4) . The intrachain metal-metal separation is 5.960(1) Å. Variable-temperature magnetic susceptibility data in the temperatyre range 290–4.2 K show that the iron(II) is high-spin and interacts in an antiferromagnetic fashion, the relevant parameters being

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. The magnitude of the exchange coupling compares well with that reported for other structurally characterized bpym-bridged iron(II) complexes.     

Synthesis of 5,6-dihydro-4H-1,3-oxazines from neutral and cationic platinum(II) nitrile complexes. X-ray structure of trans-[Pt(CF3){ H2CH2}(PPh3)2]BF4

The 1,3-oxazine complexes cis- and trans-[PtCl₂{ C(R)OCH₂CH₂C}H₂₂] (cis: R=CH₃ (1a), CH₂CH₃ (2a), (CH3)₃C (3a), C₆H₅ (4a); trans:R =CH₃ (1b), C₆H₅ (4b)) were obtained in 51-71% yield by reaction in THF at 0 °C of the corresponding nitrile complexes cis- and trans-[PtCl2(NCR)₂] with 2 equiv. of ⁻OCH₂CH₂CH₂Cl, generated by deprotonation of 3-chloro-1-propanol with n-BuLi. The cationic nitrile complexes trans-[Pt(CF₃)(NCR)(PPh₃)₂]BF₄ (R=CH3, C₆H₅) react with 1 equiv, of ⁻ OCH2CH2CH2Cl to give a mixture of products, including the corresponding oxazine derivatives trans-[Pt(CF₃){ CH₂}(PPh₃)₂]BF₄ (5 and 6), the chloro complex _trans- [Pt(CF₃)Cl(PPh₃)₂] and free oxazine H2. For short reaction times (c. 5–15 min) the oxazine complexes 5 and 6 could be isolated in modest yield (37–49%) from the reaction mixtures and they could be separated from the corresponding chloro complex (yield 40%) by taking advantage of the higher solubility of the latter derivative in benzene. For longer reaction times (> 2 h), trans-[Pt(CF₃)Cl(PPh₃)₂] was the only isolated product. Complex 6 was crystallographically characterized and it was found to contain also crystals of trans- [PtCl{ H₂}(PPh₃)₂]BF₄, which prevented a more detailed analysis of the bond lengths and angles within the metal coordination sphere. The 1,3-oxazine ring, which shows an overall planar arrangement, is characterized by high thermal values of the carbon atoms of the methylene groups indicative of disordering in this part of the molecule in agreement with fast dynamic ring processes suggested on the basis of ¹H NMR spectra. It crystallizes in the trigonal space group P , with a=22.590(4), b=15.970(3) Å, γ=120°, V=7058(1) ų and Z=6. The structure was refined to R=0.059 for 3903 unique observed (I3σ(I)) reflections. A mechanism is proposed for the conversion of nitrile ligands to oxazines in Pt(II) complexes.     

Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu₄(PAP)₂(μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(μ₂-CH₃OH)₂(N₃)₄ (1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu₄(PAP3Me)₂ (μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(H₂O)₂(NO₂)₂]- (NO₃)₂ (2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ₂-1,1-azide intramolecular bridges, and two μ₂-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(CF₃SO₃)]CH₃OH) (3) and [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(H₂O)(ClO₄)] (4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ₂-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ₂-1,1-azide bridging interactions. Intramolecular Cu-N₃-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, respectively), in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a = 26.71(1), b = 13.51(3), c = 16.84(1) Å, β = 117.35(3)° and R = 0.070, R_w = 0.050. 3 crystallizes in the monoclinic system, space group P2₁/c with a = 8.42(1), b = 20.808(9), c = 12.615(4) Å, β = 102.95(5)° and R = 0.045, R_w = 0.039. 4crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) Å, = 100.65(4), β = 101.93(3), γ = 87.82(3)° and R = 0.038, R_w = 0.036 . The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in χ_m (80 K (1), 65 K (2)), but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2J = 768(24) cm⁻¹ (3); − 2J = 829(11) cm⁻¹ (4)).     

Characterization of a dinuclear Mn(II) tri(μ-carboxylato) complex with the hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (=TpPr2) ligand: intramolecular hydrogen bonding interaction between the protonated TpPr2 and Mn-coordinating carboxylate ligands

A dinuclear Mn(II) di(μ-hydroxo) complex having hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (=Tp^iPr₂) reacted with benzoic acid to yield a dinuclear Mn(II) tri(μ-carboxylato) complex, Tp^iPr₂Mn-(μ-OBz)₃-Mn(Tp^iPr₂H). X-ray crystallography reveals the unsymmetrical coordination environments for the manganese centers. One of the two Tp^iPr₂ ligands, which bound to the five-coordinated Mn center, is protonated by the action of the third carboxylic acid and the resulting non-Mn-binding N–H moiety forms an intramolecular hydrogen bond with the oxygen donor of a carboxylate ligand. Steric congestion in the bimetallic core results in the large separation of the manganese centers bridged by the syn-anti carboxylate ligand.