Chromium(III) complexes with 1,5,9-triazanonane (3,3-tri) - CrX3(3,3-tri)n+ and CrCl(diamine)(3,3-tri)2+

The reaction of CrCl₃ · 6H₂O (dehydrated in DMSO) with 1,5,9-triazanonane (3,3-tri) gives mer- CrCl₃(3,3-tri), the configuration being established by isomorphism with the corresponding Co(III) complex. This non-electrolyte is hydrolyzed in aqueous acidic solution and mer-[CrCl₂(3,3-tri)- (OH₂)]ClO₄ can be isolated by anation with HCl in the presence of HClO₄. Reaction of mer-CrCl₃- (3,3-tri) in DMF with diamines produces complexes of the type [CrCl(diamine)(3,3-tri)] Cl₂ [diamine= 1,2-diaminoethane (en), 1.2-diaminopropane (pn), 1,3-diaminopropane (tn), 2,2-dimethyl-1,3-diaminopropane (Me₂tn) and cyclohexanediamine (chxn, cis plus trans mixture; two isomers A and B)] and these have been characterized as the ZnCl₄²⁻ salts. The configuration of the triamine ligand in these complexes has been established as mer-(H↓)- by a single crystal X-ray analysis of [CrCl(en)(3,3-tri)]- ZnCl₄, monoclinic, P2₁, a=7.932, b= 14.711, c= 8.312 Å, β=104.6° and Z=2, refined to a conventional R factor of 0.034. The kinetics of the Hg²⁺- assisted chloride release from [CrCl(diamine)(3,3- tri)]ZnCl₄ salts were measured spectrophotometrically (μ=1.0 M HClO₄ or HNO₃) over 15 K temperature ranges to give, in order, 10⁴k_Hg (298.2 K) (M⁻¹ s⁻¹), E_a(kJ mol⁻¹), ΔS^# (J K⁻¹ mol⁻¹): en- (HClO₄): 5.95, 78.1, -53; pn(HClO₄); 5.24, 81.2; -44; tn(HClO₄): 26.7, 85.6, -15; Me₂tn(HClO₄): 21.8, 78.6, -40; A-chxn(HNO₃): 7.60, 81.0,-41; B-chxn(HNO₃): 18.3, 56.8, -115. A ‘non-replaced ligand effect’ on the rate is observed for the first time in this series of homologous Cr(III) complexes. The kinetics of the thermal aquation (k_H, 0.1 M HClO₄) were measured titrimetrically for CrCl(diamine) (3,3-tri)²⁺ to give the following kinetic parameters: diamine=en: 10⁷ k_H (298.2)=5.34 s⁻¹, E_a=99.2 kJ mol⁻¹, ΔS^#=-40 J K⁻¹ mol^-1; diamine =tn: 10⁷ k_H (298.2)=5.04 s⁻¹, E_a= 82.8, ΔS^#= -96.     

1D/2D coordination polymers of copper(II) having two superexchange pathways: syntheses, crystal structures and magnetic properties

Two new polynuclear complexes of Cu(II), [(μ-1,1,3-N₃)₂{Cu₂(me₂tn)₂(N₃)₂}]_n (1) (me₂tn=2,2-dimethylpropane-1,3-diamine) and [Cu₂(μ-C₂O₄)(μ-N₃)(ipr₂en)₂]_n(ClO₄)_n (2) (ipr₂en=N,N^′-di-isopropylethane-1,2-diamine) have been synthesized and structurally characterized by X-ray crystallography. The crystal structure of 1 displays a 2D network in which distorted octahedral copper(II) centers, chelated by a me₂tn ligand and bound to a terminal azide, are connected through μ-1,1,3 bridging azide anions. The structure of 2 shows 1D chains comprising alternating [(ipr₂en)Cu-Ox-Cu(ipr₂en)] units and end-to-end azide ligand. The chains on mutual H-bonding interaction through ClO₄⁻, give rise to a 2D supramolecular architecture. The magnetic data of complexes were recorded in the temperature range, 300-2 K. In case of complex 1, the magnetic data are consistent with a ferromagnetic interaction through the end-on azide bridge (J_FM=10 cm⁻¹) and a weak antiferromagnetic interaction (zj=−0.8 cm⁻¹) between the ferromagnetically coupled dimers and an average g-value of 2.05. The susceptibility data of 2 were fitted using an alternating AF-AF chain spin 1/2 law which leads to the following parameters J_oxalate=−180 cm⁻¹, J_azide=−43 cm⁻¹ and g=2.25 cm⁻¹.     

Exchange of isonitrile ligands in the complex [Mo(O)Cl(CNMe)4] by the tetraphos ligand prP4: Stereochemical influences on the reaction course

Reaction of [Mo(O)Cl(CNMe)₄]⁺ with the linear tetraphos ligand meso and rac prP₄ leads to a mixture of [Mo(O)Cl(κ⁴-meso-prP₄)]⁺ and [Mo(O)Cl(CNMe)(κ³-rac-prP₄)]⁺ which are identified by X-ray structural analysis and/or ³¹P NMR spectroscopy. In the meso κ⁴-product both of the phenyl groups of the central phosphorus atoms are oriented towards the oxo ligand whereas in the rac κ³-product one of these phenyl groups is oriented to the oxo and the other to the chloro ligand. The origin of the different coordination modes lies in the different steric demands of the oxo and chloro ligands. The influences of the steric interactions are enhanced by the fact that exchange of the fourth isonitrile is difficult. This hypothesis is supported by the preparation of the complex [Mo(O)Cl(CNMe)(dpepp)]PF₆ whose isonitrile ligand is inert towards exchange by monophosphines, even under drastic conditions.     

Synthesis and X-ray crystal structure of a polymeric copper(II) complex containing the novel ligand 4,4-(1,4-phenylene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole]

The synthesis and X-ray crystal structure of the complex {[Cu^II(Ph₂PBPT)(bpy)](ClO₄)₂ · 2DMF}_∞ where Ph₂PBPT=4,4^′-(1,4-phenylene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole], bpy=2,2^′-bipyridine and DMF=N,N-dimethylformamide are reported. In this one-dimensional coordination polymer the Cu²⁺ ions are in a distorted octahedral N₆ coordination environment made up of two Ph₂PBPT molecules, each chelating via one pyridine and one triazole nitrogen, and one bpy co-ligand. Within the zig-zag chain thus formed the shortest distance between two metal centres across the Ph₂PBPT ligand is 13.305(3) Å while it is 10.009(3) Å between two chains. This complex represents the first structurally characterised example of a coordination compound incorporating a chelating 4,4^′-bis(4H-1,2,4-triazole) as a ligand.     

Ligand exchange reactions between copper(II) and nickel(II) chelates of different sulphur and selenium containing ligands. VII. Single-crystal ESR study on the mixed ligand chelate system Ph4As[Cu/Zn(mnt)(Et2dtc)] and crystal and molecular structure of Ph4As[Zn(mnt)(Et2dtc)]

The synthesis and crystal and molecular structure of the first zinc(II) mixed ligand chelate containing a dithiolene ligand (maleonitriledithiolate) and N,N- diethyldithiocarbamate are reported. The compound Ph₄As[Zn(mnt)(Et₂dtc)] crystallizes monoclinic, space group P2₁/c with four molecules in the unit cell; a=17.834(3), b=12.056(2), c=16.171(4) Å, β=93.73(2)°.The coordination geometry of the ZnS₄ unit is nearly tetrahedral, with a dihedral angle of 87.6° between the chelate rings. The structure is compared with those of both the patent compounds (Ph₄- As)₂[Zn(mnt)₂] and Zn₂(Et₂dtc)₄. Ph₄As[Zn(mnt)(Et₂dtc)] could be used as the host lattice in single- crystal ESR investigations of the planar Cu mixed ligand complex. The rhombic spin-Hamiltonian parameters g and A^Cu are indicative of a low symmetry of the incorporated [Cu(mnt)(Et₂dtc)]⁻ complex anions. In order to substantiate the experimental findings about the actual structure of the copper molecules, the principal values of g and A^Cu were recalculated by means of Extended Hückel MO calculations. However, the calculations performed for the dihedral angles between the ligand planes varying between 0° and 90° suggest that the rotation of the ligands is not larger than 10°     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

Metal—phenoxyalkanoic acid interactions. Part 14. The crystal and molecular structures of diaquabis(4-fluorophenoxyacetato)copper(II) bis(4-fluorophenoxyacetic acid)dihydrate and tetra-μ-(4-fluorophenoxyacetato-0,0′)-bis[(2-aminopyrimidine)copper(II)]

The crystal structures of two copper(II) complexes of 4-fluorophenoxyacetic acid (4-FPAH) have been determined by X-ray diffraction. [Cu(4-FPA)₂(H₂O)₂]·2(4-FPAH)·2H₂O (1) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 14.808(2), b = 9.832(2), c = 6.847(2) Å, α = 87.77(2), β = 98.41(2), γ = 112.33(2)° and was refined to a residual of 0.038 for 1697 ‘observed’ reflections. The coordination sphere in this complex is tetragonally distorted octahedral comprising two waters [CuO, 1.940(3) Å], two unidentate carboxylate oxygens [CuO, 1.942(2) Å] and two ether oxygens [CuO, 2.471(2) Å]. Two adducted [4-FPAH] acid molecules are linked to the un-coordinated oxygens of the acid ligands by hydrogen bonds [2.547(4) Å]. [Cu₂(4-FPA)₄(2-aminopyrimidine)₂] (2) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 12.688(2), b = 11.422(2), c = 7.951(1) Å, α = 78.74(1), β = 107.51(1), γ = 75.78(1)°, and was refined to a residual of 0.042 for 2683 ‘observed’ reflections. (2) is a centrosymmetric tetracarboxylate bridged dimer with four similar CuO (equatorial) distances [1.967–1.987 Å; 1.977(3) Å mean] and the axial position occupied by the hetero nitrogen of the 2-aminopyrimidine ligand [CuN, 2.176(3) Å]. The Cu---Cu separation is 2.710(1) Å. Crystal data are also presented which confirm the isostructurality of complex (2) with [Cu₂(phenoxyacetate)₄(2-aminopyrimidine)₂], the Co^II, Mg^II and Mn^II4-fluorophenoxyacetate complexes with their phenoxyacetic and 4-chlorophenoxyacetic acid analogues, and of Cd^II4-fluorophenoxyacetate with Cd^II and Zn^II phenoxyacetates.     

Synthesis,characterization and crystal structure of 2-dimethylacetal-4-chloro-6-formylphenol and aquabis(2-dimethylacetal-4-chloro-6-formylphenolato)dioxouranium(VI)

The ligand 2-dimethylacetal-4-chloro-6-formylphenol, H(ALAC), prepared by boiling 2,6-diformyl-4-chlorophenol, H(DIAL), in methanol, was reacted with uranyl acetate to obtain the complex [UO₂(ALAC)₂(H₂O)]. The ligand and the uranyl complex were characterized by X-ray crystallography, infrared, ¹H NMR and electronic spectroscopy. Thermogravimetric and mass spectrometry data are also reported. In acid media H(ALAC) transforms easily into H(DIAL). H(ALAC) is monoclinic, P2₁/n, with a=13.951(5), b=7.902(5), c=9.465(5) Å, β= 91.33(3)°. The structure was refined to R=3.9%, based on 1657 observed reflexions. [UO₂(ALAC)₂(H₂O)] is tetragonal, P4₃2₁2, with a=11.147(5) and c=19.150(4) Å. The structure was refined to R=4.0%, based on 2938 observed reflexions. Four ligand oxygens and one water molecule are equatorially bonded to the uranyl group in this compound. Uranium and water oxygen lie in special positions on a crystallographic twofold axis so that the two halves of this molecule are symmetrically related. Selected bond distances for [UO₂(ALAC)₂(H₂O)] are: UO (charged) 2.28(2) Å, UO (neutral) 2.45(2) Å, UO (uranyl) 1.77(2) Å, UO (water) 2.44(4) Å.     

Synthesis and spectroscopic properties of CpRuCl(R-DAB(4e)) and CpRuCo(CO)3(R-DAB(6e)). Part XVII. X-ray structure determination of CpRuCo(CO)3(t-Bu-DAB(6e))

CpRuCl(PPh₃)₂ reacted with excess R-DAB in refluxing toluene to give CpRuCl(R-DAB(4e)) (1a: R = i-Pr; 1b: R = t-Bu; 1c: R = neo-Pent; 1d: R =p-Tol). ¹H NMR and ¹³C NMR spectroscopic data indicated that in these complexes the R-DAB ligand is bonded in a chelating 4e coordination mode.Reaction of 1a and 1b with one equivalent of [Co(CO)₄]⁻ afforded CpRuCo(CO)₃(R-DAB(6e)) (2a: R = i-Pr; 2b: R = t-Bu). The structure of 2b was determined by a single crystal X-ray structure determination. Crystals of 2b are monoclinic, space group P2₁/n, with four molecules in a unit cell of dimensions: a = 16.812(4), b = 12.233(3), c = 9.938(3) Å and β = 105.47(3)°. The structure was solved via the heavy atom method and refined to R = 0.060 and R_w = 0.065 for the 3706 observed reflections. The molecule contains a RuCo bond of 2.660(3) Å and a cyclopentadienyl group that is η⁵-coordinated to ruthenium [RuC(cyclopentadienyl) = 2.208(3) Å (mean)]. Two carbonyls are terminally coordinated to cobalt (CoC(1) = 1.746(7) and CoC(2) = 1.715(6) Å) while the third is slightly asymmetrically bridging the RuCo bond (RuC(3) = 2.025(6) and CoC(3) = 1.912(6) Å). The RuC(3)O(3) and CoC(3)O(3) angles are 138.4(5)° and 136.5(5)°, respectively. The t-Bu-DAB ligand is in the bridging 6e coordination mode: σ-N coordinated to Ru (RuN(2) = 2.125(4) Å), μ₂-N′ bridging the RuCo bond and η²-CN coordinated to Co (RuN(1) = 2.113(5), CoN(1) = 1.941(4) and CoC(4) = 2.084(5) Å). The η²-CN′ bonded imine group has a bond length of 1.394(7) Å indicating substantial π-backbonding from Co into the anti-bonding orbital of this CN bond.¹H NMR spectroscopy indicated that 2a and 2b are fluxional on the NMR time scale. The fluxionality of 6e bonded R-DAB ligands is rarely observed and may be explained by the reversible interchange of the σ-N and η²-CN′ coordinated imine parts of the R-DAB ligand.     

Synthesis and characterization of an N-coordinated amidate copper(II) complex of deprotonated N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide

The title ligand, N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide (DIPMAE-H), was prepared by a nucleophilic substitution reaction between N-(2,6-diisopropyl)phenyl-2-bromoethanamide and bis-(2-pyridylmethyl)amine. An analogous ligand (TBPMAE-H) in which the 2,6-diisopropylphenyl group was substituted for a tert-butyl group was also prepared in this manner. Then, [(DIPMAE-H)CuBr]⁺Br⁻ and [(TBPMAE-H)CuBr]⁺Br⁻ were prepared by heating one equivalent of ligand and CuBr₂ in CH₃CN. In both compounds the geometry about the copper center is square pyramidal with distortions due to the geometrical constraints of the ligand. The amide oxygen occupies the axial position, and the three amine nitrogens and the bromide ligand form the basal plane of the square pyramid. Pairs of complexes in the unit cell are associated via weak donation of a lone pair on the bromide ligand of one complex to the copper center of another (Cu?Br distances in the range of 3.3576-3.4022 Å).The title compound, (DIPMAE)CuBr, was prepared by deprotonation of [(DIPMAE-H)CuBr]⁺Br⁻ using NaH. The key feature of (DIPMAE)CuBr is the amidate group η¹- and N-coordinated to the copper center. The compound also exhibits distorted trigonal bipyramidal coordination geometry with the bromide and tertiary amine donors occupying the axial sites and the amidate and pyridyl donors occupying the equatorial positions. The copper atom is displaced from the trigonal plane towards the bromide donor apex due to the geometrical demands of the ligand.     

Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M₂(Altrz)₅(NCS)₄], and for Co(II) and Ni(II) with composition [M₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂. The crystal structure of [Co₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂ was solved at room temperature. It crystallizes in the monoclinic space group P2₁/n. The lattice constants are a = 18.033(3) Å, b = 13.611(2) Å, c = 15.619(3) Å, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 Å), one terminal triazole nitrogen (CoN = 2.12 Å) and two N-bonded NCS anions (CON = 2.08 Å). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H₂O (CoO = 2.15 Å). The crystal structure is stabilised by hydrogen bonding through H₂O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of ?0.4 cm^?1, ?10.9 cm^?1 and ?8.7 cm^?1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn₂(Altrz)₅(NCS)₂]∞[Zn(NCS)₄], [Cu₂(Altrz)₃(NCS)₄]∞ and [Cd₂(Altrz)₃(NCS)₄]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.     

Synthesis and in vivo evaluation of [18F]2-(4-(4-(2-(2-fluoroethoxy)phenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)-dione ([18F]FECUMI-101) as an imaging probe for 5-HT1A receptor agonist in nonhuman primates

The 5-HT_1AR partial agonist PET radiotracer, [¹¹C]CUMI-101, has advantages over an antagonist radiotracer as it binds preferentially to the high affinity state of the receptor and thereby provides more functionally meaningful information. The major drawback of C-11 tracers is the lack of cyclotron facility in many health care centers thereby limiting widespread clinical or research use. We identified the fluoroethyl derivative, 2-(4-(4-(2-(2-fluoroethoxy)phenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)dione (FECUMI-101) (K_i = 0.1 nM; E_max = 77%; EC₅₀ = 0.65 nM) as a partial agonist 5-HT_1AR ligand of the parent ligand CUMI-101. FECUMI-101 is radiolabeled with F-18 by O-fluoroethylation of the corresponding desmethyl analogue (1) with [¹⁸F]fluoroethyltosylate in DMSO in the presence of 1.6 equiv of K₂CO₃ in 45 ± 5% yield (EOS). PET shows [¹⁸F]FECUMI-101 binds specifically to 5-HT_1AR enriched brain regions of baboon. The specificity of [¹⁸F]FECUMI-101 binding to 5-HT_1AR was confirmed by challenge studies with the known 5-HT_1AR ligand WAY100635. These findings indicate that [¹⁸F]FECUMI-101 can be a viable agonist ligand for the in vivo quantification of high affinity 5-HT_1AR with PET.     

N-{2-(4-methoxyphenyltelluro)ethyl}morpholine (L1) and its platinum(II) and ruthenium(II) complexes. Synthesis and crystal structure of L1 and trans-[PtCl2(L1)2]

The first tellurated derivative of morpholine, N-{2-(4-methoxyphenyltelluro)ethyl}morpholine (L¹) has been synthesized by reacting in situ generated ArTe⁻ with 4-(2-chloroethyl)morpholine hydrochloride under N₂ atmosphere. The compound L¹ gives molecular ion peak at m/z 351 and is characterized structurally. The donor atoms N and Te in compound L¹ are rightly oriented for its ligation in bidentate mode. The TeC(alkyl) is 0.02 Å longer than TeC(aryl). The complexes of ligand L¹ having composition [PtCl₂(L¹)₂] (1) and [RuCl₂(p-cymene)L¹] (2) have been synthesized. The compound 1 has been characterized structurally. The Pt has a square planar geometry in complex 1 and two molecules of ligand L¹ bonded through Te alone are trans to each other (PtTe=2.583(2) Å). The ¹³C{¹H} NMR spectrum of complex 1 is as expected. The ¹H NMR spectrum of single crystals of complex 1 shows multiplication of signals, which is supported by HETCOR experiments. The complex 2 also has ligand L¹ in a monodentate coordination mode, bonded through Te alone. This is supported by deshielded CH₂Te and ArCTe signals in ¹H and ¹³C{¹H} NMR spectra of complex 2 with respect to those of free ligand L¹. The HETCOR spectrum of complex 2 has been used to authenticate the assignments of CH₂Te group, as its two protons appear to be magnetically non-equivalent.     

Monomeric molybdenum(V) complexes. 4. The structure of tetraphenylarsonium oxodichloro(N-2-oxophenylsalicylideniminato)molybdate(V), [Ph4As] [MoOCl2(SalphO)]

The structure of [Ph₄As] [MoOCl₂(SalphO)], where SalphO is N-2-oxophenylsalicylideniminate dianion, has been determined by X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/n with a = 11.829(2), b = 16.149(3), c = 17.410(3) Å, β = 97.485(15)° and Z = 4. The calculated and observed densities and 1.566 and 1.573(10) g cm^?3, respectively. Block-diagonal least-squares refinement of the structure using 4722 independent reflections with I ? 3σ(I) converged at R = 0.0345 and R_w = 0.0484. The crystal contains [Ph₄As]⁺ cations and [MoOCl₂(SalphO)]^? anions. The Mo atom in the anion is in a distorted octahedral coordination environment. A planar terdentate Schiff base ligand occupies meridional positions with the N atom trans to the terminal oxo group (O_t). Two Cl atoms are cis to the O_t atom. The Mo atom is displaced by 0.33 Å from the equatorial plane toward the O_t atom. The MoO_t distance is 1.673(3) Å. The MoN bond trans to the O_t atom is 2.298(4) Å. The two MoCl bond lengths are 2.371(1) and 2.408(1) Å. The difference of 0.037 Å is significant (30 σ). Preparations of the title complex and the related complexes are also described.     

Novel six-coordinate oxorhenium(V) ‘3+2’ mixed-ligand complexes carrying the SNO/SN donor atom set

Ligand exchange reactions of oxorhenium(V) precursors with bidentate SN and tridentate Schiff bases derived from the condensation of ketones or aldehydes with dithiocarbazic acid methyl ester (H₂NNHC(S)SCH₃) produce novel ‘3+2’ mixed-ligand complexes carrying the SNO/SN donor atom set. Thus, reactions of either [NBu₄][ReOCl₄] or Na[ReO(Gluconate)₂] with SNO ligands (H₂Lⁿ) or a mixture of bidentate SN (HL^m) and tridentate SNO (H₂Lⁿ) in methanol solutions lead, respectively, to the six-coordinated mixed ligand oxorhenium(V) compounds of types [ReO(Lⁿ)(HLⁿ)] and [ReO(Lⁿ)(L^m)], combining one tridentate dianionic S⁻NO⁻ donor Schiff base (L) and one bidentate anionic S⁻N donor ligand (HL). Coordination geometry around rhenium is distorted octahedral with the two SN donor atom sets of each ligand defining the equatorial plane, while apical positions are occupied by the oxo group and the oxygen atom of the tridentate SNO ligand (L), as shown by single-crystal X-ray diffraction structure of [ReO(L¹)(HL¹)] 1.     

Synthesis, characterization, thermal behavior, and DNA-cleaving studies of cyano-bridged nickel(II)-copper(II) complexes of 4-(pyridin-2-ylazenyl)resorcinol

We present here the syntheses of a mononuclear Cu^II complex and two polynuclear Cu^II Ni^II complexes of the azenyl ligand, 4‐(pyridin‐2‐ylazenyl)resorcinol (HL; 1). The reaction of HL ( 1 ) and copper(II) perchlorate with KCN gave a mononuclear complex [CuL(CN)] ( 4 ). Using 4 , one pentanuclear complex, [{CuL(NC)}₄Ni](ClO₄)₂ ( 5 ) and one trinuclear complex, [{CuL(CN)}₂NiL]ClO₄ ( 6 ), were prepared and characterized by elemental analyses, magnetic susceptibility, molar conductance, IR, and thermal analysis. Stoichiometric and spectral results of the mononuclear Cu^II complex indicated that the metal/ligand/CN ratio was 1 : 1 : 1, and the ligand behaved as a tridentate ligand forming neutral metal chelates through the pyridinyl and azenyl N‐, and resorcinol O‐atom. The interaction between the compounds (the ligand 1 , its Ni^II and Cu^II complexes without CN, i.e., 2 and 3 , and its complexes with CN, 4 – 6 ) and DNA has also been investigated by agarose gel electrophoresis. The pentanuclear Cu₄Ni complex ( 5 ) with H₂O₂ as a co‐oxidant exhibited the strongest DNA‐cleaving activity.     

Isolation of [{HB(Me2pz)3}MoO2(OC6H4S)]2, a binuclear Mo(VI) complex containing a disulfide bond

Aerial recrystallization of the mononuclear molybdenum(V) complex {HB(Me₂pz)₃}MoO(OC₆H₄-o-S) produced the novel binuclear Mo(VI) complex [{HB(Me₂pz)₃}MoO₂(OC₆H₄- o-S)]₂ which contains a disulfide bond. The dimer crystallizes as the dioxane solvate in the space group C2/c with cell parameters a=23.46(2), b=11.100(4), c=21.571(8) Å, β=104.23(4)°, Z=4. Final R_w=0.062 (2236 reflections with F_o>3σ(F_o), 301 variable parameters). The dimer contains two crystallographically identical distorted octahedral MoO₂²⁺ centers. One face of each octahedron is occupied by two oxo ligands and a phenolate oxygen atom; the opposite face is occupied by three nitrogens of the HB(Me₂pz)₃⁻ ligand. The two Mo(VI) centers of the dimers are linked by a disulfide bond formed upon oxidation of the 2-mercaptophenolate ligand of the original molybdenum(V) compound.     

Preparation of a new 16-MC-4 structure type that captures Mn(II) in the central cavity

Bernhard Lippert has contributed significantly to the understanding of metallamacrocyclic complexes with low valent, late transition metals. In particular, he has pioneered the preparation of metallacalixarenes such as 12-MC-3 and 16-MC-4 structure types. In this article, we provide the preparation of a new 16-MC-4, [Mn₄Br₄(B(^tBuM)PZG)₄] [Mn(HOCO₂)₂], complex made with the ligand potassium N,N-bis(3-methyl-5-tert-butylpyrazolylmethyl)glycinate (KB(^tBuM)PZG). In addition to being the first 16-MC-4 that is composed of manganese, this complex is the first example of a transition metal [Mn(II)] being captured in the interior cavity of the 16-MC-4. We discuss how our ligand design leads to the isolated structure due to the steric bulk that has been appended to the pyrazole ligand.     

Kinetics of CO substitution in Co4(CO)12 and Rh4(CO)12

The kinetics of rapid CO substitution by PPh₃ in Co₄(CO)₁₂ and Rh₄(CO)₁₂ have been examined by stopped-flow and low temperature FT-IR methods. In Co₄(CO)₁₂ rapid (k_obs ∼ 1.8 s⁻¹) substitution of CO occurs after a 1–15 s induction period at 28 °C in C₆H₅Cl solvent by a catalytic process. Addition of PPh₃ to Rh₄(CO)₁₂ yields Rh₄(CO)₁₁(PPh₃) according to a predominantly second order rate law k₁[Rh₄- (CO)₁₂] + k₂[Rh₄(CO)₁₂][PPh₃] with k₁ = 25 ± 11 s⁻¹ and k₂ = 2.97 ± 0.27 X 10⁴ M⁻¹ s⁻¹ at 28 °C. Substitution of a second CO ligand also occurs rapidly with k₁ = 0.15 ± 0.09 s⁻¹ and k₂ = 6.54 ± 0.07 X 10² M⁻¹ s⁻¹ at 28 °C. The reactivity of Rh₄(CO)₁₂ toward associative substitution is 10⁴– 10¹¹ faster than for the Co and Ir analogues, In Rh₄(CO)₁₁(PPh₃) the increase in CO substitution rates over Co and Rh analogues is 10²–10⁷. The ordering of associative substitution rates Co << Rh >>> Ir in these clusters exaggerates the trend seen in mononuclear metal complexes.     

The relationship between the structures of periphery ligands and the DNA binding mode of [Ru(II)(1,10-phenanthroline)(L1L2)dipyrido[3,2-a:2',3'-c]phenazine](n+) (L1=Cl or pyridine and L2=pyridine, n=1,2)

The binding modes of the [Ru(II)(1,10-phenanthroline)(L₁L₂) dipyrido[3,2-a:2′,3′-c]phenazine]²⁺ {[Ru(phen)(py) Cl dppz]⁺ (L₁ = Cl, L₂ = pyridine) and ([Ru(phen)(py)₂dppz]²⁺ (L₁ = L₂ = pyridine)} to native DNA is compared to that of the [Ru(II)(1,10-phenanthroline)₂dipyrido[3,2-a:2′,3′-c]phenazine]²⁺ complex ([Ru(phen)₂dppz]²⁺) by various spectroscopic and hydrodynamic methods including electric absorption, linear dichroism (LD), fluorescence spectroscopy, and viscometric titration. All measured properties, including red-shift and hypochromism in the dppz absorption band, nearly perpendicular molecular plane of the dppz ligand with respect to the local DNA helix axis, prohibition of the ethidium binding, the light switch effect and binding stoichiometry, increase in the viscosity upon binding to DNA, increase in the melting temperature are in agreement with classical intercalation of dppz ligand of the [Ru(phen)₂dppz]²⁺ complex, in which both phenanthroline ligand anchored to the DNA phosphate groups by electrostatic interaction. [Ru(phen)(py)₂ dppz]²⁺ and [Ru(phen)(py) Cl dppz]⁺ complexes had one of the phenanthroline ligand replaced by either two pyridine ligands or one pyridine plus a chlorine ion. They exhibited similar protection from water molecules, interaction with DNA bases, and occupying site that is common with ethidium. The dppz ligand of these two Ru(II) complex were greatly tilted relative to the DNA helix axis, suggesting that the dppz ligand resides inside the DNA and is not perpendicular relative to the DNA helix axis. These observation suggest that anchoring the [Ru(phen)₂dppz]²⁺complex by both phenanthroline is essential for the dppz ligand to be classically intercalated between DNA base-pairs.