Ligand Field Spectra Research Articles

Optical properties of Ni[ tbu 2P(O)NR] 2: A paramagnetic d 8 complex with planar structure

The title complexes of Ni(II) with trans-planar structure are paramagnetic because they have a triplet ground state (R = i-propyl, green isomer of c-hexyl) or there is another electronic level closely located above the singlet ground state which is available by thermal energy kT (R = t-butyl). Angular overlap model (AOM) calculations are able to interpret these ground states as well as the ligand field spectra measured from the crystals in the near-IR and visible region. For this the model must be extended considering metal ion s-d orbital mixing for a NiN 2O 2; chromophore. A fitting of absorption peaks to theoretical transition energies supplies AOM parameters e σ, e π and e sdσ of ligands with oxygen and nitrogen donor atoms which compare well to parameter values of other ligands of similar nature, as far as these are known.

Theoretical analysis of the ligand field spectrum of K 3CoF 6

We present a detailed ab initio study of the ligand field spectrum of the CoF 3− 6 cluster in the K 3CoF 6 crystal. The crystal environment around the octahedral CoF 3− 6 cluster is accounted for by a Madelung potential. The ground and ligand field excited states of K 3CoF 6 have been studied with the inclusion of correlation effects. Each state was first optimized separately in a complete active space self-consistent field (CASSCF) calculation, including ten active electrons occupying the bonding e g and anti-bonding e * g and t * 2g shells. Further correlation was incorporated by using the averaged coupled pair functional approach (ACPF) with the CASSCF configuration space as reference space and where the maximum number of correlated electrons was up to twenty. The one quintet-quintet transition is already described well at the CASSF level while the spin-forbidden quintet-triplet transitions require the inclusion of dynamical correlation.

Neutral transition metal complexes with the tridentate ligand 4-(5-methyl-4-imidazolyl)-3-thiabutanoic acid. A series of isostructural octahedral compounds

The synthesis and spectroscopic properties of the iron, cobalt, nickel and copper complexes with the ligand 4-(5-methyl-4-imidazoly)-3-thiabutanoic acid (abbreviated Hitba) are described. The compound Co(itba) 2 ( A) crystallizes in the triclinic space group P1 with a=7.600(1), b=7.697(1), c=8.2696(5) Å, α=86.745(8),β=71.321(7), γ=69.538(12)°, V=428.5 Å 3, D x=1.65 g/cm 3 for Z=1. The compound Cu(itba) 2 ( B) crystallizes in the triclinic space group P1 with a=7.789(3), b=7.794(4), c=8.138(4) Å, α=71.448(4), β=86.905(4), η=67.805(4)°, V=432.4 Å 3, D x=1.66 g/cm 3 for Z=1. In both structures the metal ion is located on the inversion centre because of symmetry considerations. The non-hydrogens were located using Fourier methods and the structures were refined by least-squares methods to residual R w values of 0.089 ( A) and 0.050 ( B). The coordination geometry of the metal ion in both compounds A and B is octahedral with the donor atoms of the two ligands in mutual trans positions. The bond distances in the cobalt compound are significantly different from those in the Jahn-Teller distorted copper compound (CoN=2.109(7), CuN=1.986(3); CoO=2.065(6), CuO=1.988(2); CoS=2.501(2), CuS=2.7146(8)). The geometry of the cobalt ion can be described as a rather regular octahedron compared with the elongated octahedral copper structure. The obtained compounds M(itba) 2 are all isostructural according to their X-ray powder patterns and IR spectra, and all show remarkably strong ligand field spectra.

Systematic ab initio study of the ligand field spectra of hexacyanometalate complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSystematic ab initio study of the ligand field spectra of hexacyanometalate complexesK. Pierloot, E. Van Praet, L. G. Vanquickenborne, and B. O. RoosCite this: J. Phys. Chem. 1993, 97, 47, 12220–12228Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/j100149a021RIGHTS & PERMISSIONSArticle Views294Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

A cellular ligand-field model for ‘l-l’ spectral intensities

The transition energies and intensity distributions in the ligand-field spectra of K2PtCl4 and K2PtBr4 are quantitatively reproduced within the cellular ligand-field approach. The energy and intensity parameters provide a realistic and consistent account of the electron distribution in these third row transition-metal chromophores. The intensity arises dynamically through the molecular vibration modes. The parameters for the three ungerade bending modes in the molecular D 4h symmetry are of similar magnitude, a result that is consistent with the nearly equal frequencies of these vibrations. Analyses of the transition energies of the analogous palladium(II) complexes are consistent with the studies of the platinum(II) species.

Spectroscopic analysis, coordination geometry, and x-ray structures of nickel(II) compounds with sterically demanding tris(pyrazolyl)borate ligands and azide or (thio)cyanate anions. Crystal and molecular structures of bis[(.mu.-thiocyanato-N,S)(hydrotris(3-isopropyl-4-bromopyrazol-1-yl)borato)nickel(II)]-3-heptane and (thiocyanato-N)(hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borato)nickel(II)

Ligand-field spectra and infrared spectra of compounds with stoichiometry M(LLL)X, where X is one of the pseudohalides NCS - , NCO, and N 3 - , LLL - is a tridentate-substituted pyrazolylborate monoanionic ligand, and M=Ni (as well as a number of Co and Zn compounds for comparison), are described. [Ni{HB[N 2 C 3 H(Me)(C 4 H 9 )] 3 }(NCS)] crystallizes in P2 1 /n with a=9.594, b=17.429, c=17.933A, β=98.43°, Z=4. [Ni{HB[N 2 C 3 H(Br)(C 3 H 7 )] 3 }(NCS-μ-N,S)] 2 .3C 7 H 16 crystallizes in C2/c with a=21.301, b=12.740, c=30.198A, β=107.04°.

The effect of the crystal environment on the metal–ligand interaction and the ligand field spectrum of CrF3−6

The octahedral CrF3−6 cluster is studied in two different crystal environments. The available experimental data reveal that the cluster with the largest Cr–F bond distance is at the same time characterized by the largest value of the spectrochemical strength. This paradoxical fact has been shown to be due to the effect of the two different Madelung potentials. In K2NaCrF6, the central Cr ion is situated at a maximum of the Madelung potential; in CrF3, it is situated at a minimum. For the different crystal environments it has also been shown that the increase in covalency, that goes with the introduction of correlation, parallels the covalency that is present already at the Hartree–Fock level.

Synthesis, crystal structure and properties of two acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulfonamide) complexes: bis(5-acetamidato- 1,3,4-thiadiazole-2-sulfonamide- O)bis( 1,2-ethanediamine)copper(II) and bis(5-acetamidato-1,3,4-thiadiazole-2-sulfonamide- N)bis(1,3- propanediamine)copper(II); an unusually weak ambidentate anionic ligand

The diverse coordination chemistry exhibited by acetazolamide (H 2acm), a potent inhibitor of the carbonic anhydrase metalloenzyme, is highlighted in two new copper(II) complexes of this ligand: [Cu(Hacm) 2(en) 2] ( I) and [Cu(Hacm) 2(tn) 2] ( II). The synthesis, crystal structure and spectroscopic properties of both compounds are reported in this paper. The structures of both compounds consist of discrete units of [Cu(Hacm) 2(en) 2] ( I) and [Cu(Hacm) 2(tn) 2] ( II), respectively, interacting through van der Waals contacts and hydrogen bonds only. Hacm, however, binds differently in each compound. In both cases, the Cu(II) ions, lying on the symmetry centers, show an elongated octahedral geometry with the four 1,2-ethanediamine or 1,3-propanediamine N atoms in an approximately square coplanar arrangement (Cu-N distances of 2.00 and 2.01 Å for I; 2.04 and 2.05 Å for II); two sulfonamido O atoms in I and two thiadiazole N atoms in II, from two trans Hacm ligands, complete the distorted octahedron at the longer distance of 2.65 and 2.46 Å, respectively. Although the ligand is deprotonated at the acetamido group, in neither case is the interaction with the copper produced via the donor atoms of that group. Furthermore, in I, unexpectedly, in spite of its four potentially chelating N atoms, and in spite of the deprotonation of the acetamido group, acetazolamide acts as a monodentate ligand coordinating through one of the O atoms of the sulfonamido moiety. This behavior is completely different from that observed in II and in all acetazolamide complexes described up to now, and it must be related to hydrogen bonding and to the copper(II) Jahn-Teller effect. Stabilization of the negative charge at the deprotonated group takes place through ‘pairing’ of the Hacm ions in the packing system. These results further emphasize the many coordinating possibilities of the ligand, which could be of relevance to a proper understanding of the mechanism of inhibition in the enzyme. Crystallographic data: [Cu(C 4N 4S 2O 3H 5) 2(C 2N 2H 8) 2] ( I) (MW=626.2) crystallizes in the triclinic space group P 1 , Z=1, with the cell dimensions a=8.196(7), b=9.094(4), c=9.352(3) Å, α=84.51(3), β=74.83(6), γ=63.57(5)° and V=602 Å 3, D calc=1.73 Mg m −3; the final agreement values were R=0.0335 and R w=0.0427 for 3947 independent significant reflections. [Cu(C 4N 4S 2O 3H 5) 2(C 3N 2H 10) 2] ( II) (MW=654.3) crystallizes in the monoclinic space group P2 1/ n, Z=2, with the cell dimensions a=9.336(3), b=10.232(1), c=14.138(3) Å, β=103.80(2) and V=1312 Å 3, D calc=1.66 Mg m −3; the final agreement values were R=0.0327 and R w=0.0405 for 1932 independent significant reflections. The structures were solved by using the copper coordinates (at the inversion center) for repeated Fourier calculations (AUTOFOUR, SHELXS-86). Ligand field and EPR spectra for both complexes are in agreement with the tetragonal Cu(II)N 4O 2 ( I) and Cu(II)N 4N 2′ ( II) chromophores, respectively.

Tetrathiorhenate(VI), ReS42–. Spectroelectrochemical characterization (UV–VIS–IR) of a small new d1system and of its tetrakis(2,2′-bipyridine)diruthenium(II) complex (EPR)

ReS42– is the first d1 tetrathiometallate persistent enough to be studied with respect to change transfer, ligand field and IR vibrational spectra via spectroelectrochemistry; an EPR spectrum could only be detected of its trinuclear derivative [(bpy)2Ru(µ-ReS4)Ru(bpy)2]2+(bpy = 2,2′-bipyridine) at 4 K.

Structure, spectra and redox behaviour of copper(II) complexes of bis(benzimidazolyl)diamine ligands

The linear quadridentate ligand N,N′-bis(benzimidazol-2-ylethyl)ethane-1,2-diamine (L1) and its 1-methylbenzimidazole analogue (L2) and homologues form 1 : 1 complexes with Cu(ClO4)2; L1 also forms complexes of the types CuL1X2 where X = NO3, PF6, Br or Cl and CuL1(X)Y where X = Cl or Br and Y = ClO4 or Br. Deep blue CuL1Br2·2H2O crystallizes in the monoclinic space group C2/c with Z= 4, a= 9.919(2), b= 16.626(3), c= 14.102(3)Å and β= 94.39(2)°. The structure was solved by Patterson and Fourier difference methods and refined by the least-squres technique to R= 0.064 for 2195 independent reflections with I > 1.5σ(I). The molecule lies on a two-fold axis symmetrically around CuII. The co-ordination around CuII is found to be square planar with two amino nitrogens and two benzimidazole nitrogens forming the equatorial plane [Cu–N 1.983(3) and 2.037(4)Å]. The bromides are at longer distances [3.349(1)Å] in axial sites. Ligand field and EPR spectra indicate that one bromide or chloride ion is axially co-ordinated to CuII in [CuL1]2+. This ion exhibits quasi-reversible redox behaviour. Electrochemical studies of the dihalides in methanol have established the presence of [CuL1X2], [CuL1(X)]+ and [CuL1]2+ in equilibrium. In complexes with 565 [CuL4]2+[L4=N,N′-bis(benzimidazol-2-ylmethyl)ethane-1,2-diamine] and 555 [CuL3]2+[L3=N,N′-bis(1-methylbenzimidazol-2-ylmethyl)propane-1,3-diamine] chelate rings, CuII does not seem to lie in the N4 square plane, as revealed by their low A∥ values and irreversible electrochemical behaviour. The CuII–CuI redox potentials in methanol are in the order [CuL1]2+ < [CuL3]2+ < [CuL4]2+; this illustrates that six-membered chelate rings are suitable to stabilize CuII, when Cu–N σ interactions are favourable.

Synthesis and solution properties of some trans-cyanoacidotetraamminechromium(III) complexes

The trans-[Cr(NH 3) 4(CN)X] + ions, where X = NCS, F and Cl, have been prepared by reaction in methanol suspension of either trans-[Cr(NH 3) 4(H 2O)(CN)] 2+ with NCS − and F −, or trans-[Cr(NH 3) 4(Me 2SO)Cl] 2+ with CN −. Their perchlorate salts have been characterized by analysis, ion-exchange, conductance, absorption spectra, phosphorescence in room-temperature solution and aqueous chemistry. The solvent dependence of the ligand-field spectrum for X = F is ascribed to hydrogen bonding that affects the CrF interaction. Both π(X) → e g *(Cr) and t 2g (Cr) → π*(CN) charge-transfer transitions are observed, consistent with the π-donor and π-acceptor nature of the two axial ligands. All these complexes undergo acid-catalysed CN − aquation. When X = Cl this competes with pH-independent loss of X. The aquation products, fully stereoretentive, confirm the trans isomerism of the new species. The anation and aquation behaviours reveal trans effects of the CN − ligand.

Transition metal complexes of two related pyrazole containing ligands:3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diazaoctane (ddad) and 1,4-bis(2-ethyl-(3,5-dimethyl-1-pyrazolyl))-piperazine (bedp). Synthesis, spectroscopy and X-ray structures

Several coordination compounds with the ligand 3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diaza- octane (ddad) were obtained: (Cu, Ni)(ddad)(BF 4) 2, Co(ddad)(H 2O)(BF 4) 2, (Co, Ni, Cu, Zn) 2(ddad)Cl 4, Co 3(ddad) 2(NCS) 6 and Cu 2(ddad)(NCS) 3. Five X-ray structures were obtained, viz. of [Cu(ddad)](BF 4) 2, [Ni(ddad)](BF 4) 2, Ni(ddad)(NCS) 2, [Ni(bedp)](H 2O)(BF 4) 2 and [Cu(bedp)](H 2O)(BF 4) 2, but the data did not allow the calculation of very accurate bond lengths. However, the basic coordination geometries were obtained in all cases. The coordination by the ligands is square planar, while Ni(ddad)(NCS) 2 contains additional trans coordinating thiocyanate anions. The asymmetric unit of [Cu(ddad)](BF 4) 2 contains two almost identical [Cu(ddad)] 2+ species. The coordination of the copper atoms in both molecules is intermediate between tetrahedral and square planar. One molecule [Cu(ddad)] 2+ is the (R,R) diastereoisomer of the ligand and the other is the (S,S) diastereoisomer. The chloride compounds are, except for Ni(II), all dinuclear with MN 2Cl 2 chromophores. The nickel(II) compound contains square planar Ni(ddad) 2+ cations and tetrahedral NiCl 4 2- anions. The thiocyanate compound of Ni(II), which is isomorphous with the corresponding Zn(II) compound, has octahedral MN 2N 2′N 2″ chromophores. The cobalt compound crystallizes as [Co(ddad)(NCS)] 2Co(NCS) 4 with five coordinate cobalt in the cation. With copper thiocyanate ddad forms the mixed-valence compound Cu 2(ddad)(NCS) 3, with [Cu(ddad)] 2+ and [Cu(NCS) 3] 2-. With the ligand, 1,4-bis(2-ethyl-(3,5-dimethyl-l-pyrazolyl))-piperazine (bedp) the compounds [(Ni, Cu)Coedp)](H 2O)(BF 4) 2, (Ni, CO)Coedp)(NCS) 2, Zn 2(bedp)(NCS) 4, (Ni, Co, Cu, Zn) 2(bedp)Cl 4 and Cu 2(bedp)(NCS) 3 were obtained. The chloride compounds form dinuclear compounds (similar to ddad) with MN 2Cl 2 chromophores. However, in addition to the green form of [Ni(bedp)][NiCl 4] a purple isomer Ni 2(bedp)Cl 4, with a tetrahedral NiN 2Cl 2 chromophore, was obtained. The ligand field spectra of Ni(bedp)(NCS) 2 and the isomorphous cobalt compound show typical octahedral chromophores. With copper thiocyanate a mixed-valence compound was formed, with a structure likely to be similar to the corresponding ddad compound, viz. [Cu(II)(bedp)][Cu(I)(SCN) 3].

Metal uptake by N, N′-bis(2-benzimidazolylmethyl) amine immobilized on poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)

N,N′-bis(2-benzimidazolylmethyl)amine (bbaH) has been anchored to poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (GMA). GMA resins with various glycidyl methacrylate: ethylene glycol dimethacrylate ratios were used. Two ways of attachment were investigated. Direct coupling of the aliphatic amine of bbaH to GMA yields resins (GB) containing 0.6–0.8 mmol of the ligand per gram of resin. In contrast, a three-step reaction yields resins (GAB) containing 1.2–1.6 mmol of the ligand per gram of resin. The resin structures were confirmed by solid-state cross polarization and magic-angle spinning nuclear magnetic resonance spectroscopy, infrared spectroscopy, and elemental analyses. The metal-uptake capacities of the resins for Cu 2+ are high: 0.63 mmol Cu 2+/g of resin for GB8/2-I and 1.25 mmol Cu 2+/g of resin for GAB8/2-II at pH 5.8. The capacities for Ca 2+, Co 2+, Ni 2+, Zn 2+ and Cd 2+ are lower. For 0.08 M CuCl 2 solutions in concentrated hydrochloric acid (pH −1) the Cu 2+ capacity is still reasonably high: 0.26 and 0.43 mmol/g for GB8/2-I and GAB8/2-II, respectively. Metal-uptake experiments under competitive conditions confirm the high selectivity for Cu 2+ . Elemental analyses and spectroscopic data suggest that 1:1 (metal:ligand) complexes are formed on the polymer matrix. Ligand field and EPR spectra are consistent with a distorted square pyramidal coordination geometry of the Cu 2+ and Co 2+ complexes and a distorted octahedral coordination geometry of the Ni 2+ complex. The kinetic performance of the resins was found to depend on the resin particle size and the amount of ethylene glycol dimethacrylate in the copolymer. The method of ligand attachment, however, does not affect the kinetic properties. H 2SO 4 (1 M) was tested for its stripping potential. Stripping of Cu 2+ was found to be quite fast and dependent on the GMA used. Complete removal of Cu 2+ over 99 %), however, could only be affected for some of the resins after prolonged acid treatment, the difficulties being caused by the relatively high Cu 2+ capacities at pH 0.

Coordination compounds of the ligand 1,6-bis(3,5-dimethyl-1-pyrazolyl)-2,5-dithiahexane (bddh) with divalent nickel, cobalt and zinc salts. X-ray crystal structure of Co(bddh)(NCS) 2

The N 2S 2 ligand 1,6-bis(3,5-dimethyl-1-pyrazolyl)-2,5-dithiahexane (abbreviated bddh) forms the coordination compounds (Co, Ni, Zn)(bddh)Cl 2, (Ni, Co)(bddh)(NCS) 2 and [Ni(bddh)(NO 3) 2](H 20) 2. The X-ray crystal structure of Co(bddh)(NCS) 2 was determined at room temperature: tetragonal, space group P4 12 12, a= b=9.083(1), c=26.447(3) Å, α=β=γ=90.0°, Z=4. The structure was solved by Patterson methods and refined by least-squares calculations to the residual R values of 0.038 ( R) and 0.021 ( R w) and the goodness-of-fit of 2.27 for 4808 measured, 2313 independent and 1999 observed ( Fρ4.0σ(F)) reflections. The cobalt(II) ion is in a distorted octahedral CoN 2N′ 2S 2 geometry, in agreement with its ligand field spectrum. The ligand chelates through two pyrazole N atoms in trans position and the two sulfur atoms in cis position. The thiocyanate anions coordinate through the N atoms in a cis position. The Co-donor distances are 2.119(2) (N-pyrazole), 2.579(1) (S) and 2.026(3) (N-thiocyanate) Å. The ligand field spectra of the nickel compounds agree with octahedral coordination of the metal ion. IR spectroscopy of [Ni(bddh)(NO 3) 2](H 2O) 2 strongly suggests that both nitrate anions are monodentate and the water molecules are present in the crystal lattice. The compounds (Co, Zn)(bddh)Cl 2 are X-ray isomorphous and the ligand field spectrum of Co(bddh)Cl 2 shows a CoN 2Cl 2 chromophore.

Spectroscopic and magnetic properties of square-planar bis[(cyclooctane-1,5-diyl)bis(pyrazol-1-yl)borato]cobalt(II)

Ligand-field spectra, EPR spectra and magnetic susceptibility of the title compound are described in terms of square-planar Co(II) in the low-spin state ( S= 1 2 ). The presence of two short, agostic, CoH contacts (2.16 Å) results in a very slow relaxation, allowing the observation of EPR signals even at room temperature. This relaxation behaviour is also responsible for the fact that solid state NMR spectra ( 13C and 1H) could not be observed for this compound. The magnetic moment of 2.05(3) BM ( g av = 2.18(3)) in the 77–300 K region, agrees with the EPR g values for the powder ( g∥ = 1.65(5) and g⊥ = 2.37(5); g av =2.13(5)). Dopes of the title compound in the corresponding Zn compound (not X-ray powder isomorphous with the Co compound) and the Ni compound (powder isomorphous with Co compound), on the other hand, show quite different, and beautifully resolved EPR spectra. In the Zn lattice a very sharp EPR signal, with inverted, g values at g∥ = 2.05 (with an A∥ value of 18 Gauss) and g⊥ = 2.00, indicating a Co III)O 2 − species, appears to be present. Unfortunately, this mixed compound could not be purified through recrystallization, since on each purification step some Co(II) was lost from the lattice. In the isomorphous Ni lattice, however, the Co hyperfine splitting nicely shows up in a rhombic signal with hyperfine splittings present on each of the three g values and superhyperfine on g z ; the parameters are g x =2.68(2) ( A x = 115(5) G), g y = 2.54(4) ( A y = 135(5) G) and g z = 2.01(2) ( A z = 165(5) G; A N = 18(1) G). These EPR values differ slightly from the frozen-solution data of the pure Co compound in toluene, for which the parameters g x = 2.70 (very broad, A x unresolved), g y = 2.30(2) ( A y = 65(5) G) and g z = 2.02(2) ( A z = 150(5) G) are derived. Ligand-field spectral data of the pure Co compound are in agreement with a square-planar CoN 4 chromophore. In solutions of organic solvents, like toluene, THF and CH 2Cl 2, the colour changes somewhat and the ligand-field maxima are shifted slightly; however, no tetrahedral geometry can be deduced from these spectra, in agreement with frozen-solution EPR spectra. The ligand-field spectrum of the Co-doped zinc compound, on the other hand, shows clear bands due to tetrahedral Co(II). Solid state 1H and 13C NMR spectra of the pure Ni compound show almost the same spectrum as the diamagnetic Zn compound, indicating that the Ni(II) is indeed low spin in the solid state. No signals were found indicating the presence of agostic MH interactions. On the other hand, IR spectra clearly show CH bands indicative for agostic MH interactions, i.e. at 2690 (Co), 2780 (Cu) and 2800 (Ni) cm −1, whereas the non-isomorphous Zn compound has the CH stretching vibration at 2820 cm −1.

Coordination compounds of 5-methyl[1,2,4]triazolo[1,5- a]pyrimidin-7-ol and transition metal(II) halides. Synthesis, spectral and magnetic properties

The synthesis and spectroscopic and magnetic properties of a series of polynuclear metal coordination compounds are described. The compounds have the general formula MX 2(mtpH) 2 (with M=Mn, Fe, Co, Ni, Cu and Cd; X=Cl, Br; mtpH=5-methyl[1,2,4]triazolo[1,5- a]pyrimidin-7-ol). The IR spectra and X-ray powder-diffraction patterns indicate the presence of two structure types within the series. On the basis of their ligand-field spectra and magnetic properties a pseudo-octahedral halide-bridged linear-chain structure is derived for most of the compounds. In this structure the metal ions are surrounded by four bridging anions and two N-coordinated, mtpH ligands. Structural exceptions are MnBr 2(mtpH) 2 and CoBr 2(mtpH) 2. These compounds have a different, possibly five-coordinated, structure in which both N and O atoms of mtpH have interactions with the metal ions and/or hydrogen bonding systems.

Preparation and Spectroscopic Properties of Cofacial Binuclear Copper(II) Complex with 3, 3′-[1,3-Phenylene-bis(methylene)]bis(2,4-pentanedione)

Abstract 3, 3′-[l, 3-Phenylenebis(methylene)]bis(2, 4-pentanedione) (H2L) was prepared by the reaction of 2, 4-pentanedione and 1, 3-bis (bromomethyl) benzene. From a ratio of the intensities of the 1H n. m. r. spectrum, the keto form of H2L is about 87% and the enol form is about 13% The dicopper(II) complex (Cu2L2) of H2L was prepared. A strong i.r. band due to the C=O stretching mode is shifted toward lower energy upon the production of Cu2L2 complex. The ligand field spectrum of Cu2L2 complex is similar to that for bis(2, 4-pentanedionato)copper(II) complex and the copper atom has primarily the square-planar coordination. As judged by the e.s.r. spectra, Cu2L2 complex is the cofacial bimetallic system.

Spectroscopic characterization, electrochemistry and single-crystal structure of bis[chlorobis (dimethylphosphito- p)(hexamethylbenzene) ruthenium(II)-μ-( O,O,Cl)]Copper(II) dichloromethane (1:2), an unusual linear, heterotrinuclear complex

The X-ray crystal structure of the heterotrinuclear compound [Cu{ClRu[(MeO) 2PO] 2(C 6Me 6)} 2]·2CH 2Cl 2 is described, together with its spectroscopic and electrochemical properties. The copper ion is tetragonally coordinated by four, short copper-oxygen bonds [CuO = 1.931(4) and 1.965(4) Å] and two, long CuCl bonds of 2.881(2) Å. The chloride ions bridge directly between the copper and ruthenium, with RuCl = 2.292(2) Å and RuClCu = 93.6(1)°. The other bridging ligands are the OP(OMe) 2 − ligands, which coordinate to copper with oxygen and to ruthenium with phosphorus. The ruthenium coordination is completed by the η 6-C 6Me 6 ligand. The structure of the complex is retained in solutions of CH 2Cl 2 and CH 3CN. Electrochemical studies (CV and DPP) show that both ruthenium(II) ions can be oxidized subsequently at, respectively, 0.69 and 0.87 V. The copper(II) ion is not redox active. The compound has been further characterized by ligand-field spectra and EPR spectra for copper(II). These spectra agree with a tetragonal chromophore CuO 4Cl 2, both for the solid and the (frozen) solution.

Spectrochemical properties of noncubic transition metal complexes in solutions—IV. Energy levels of tetragonal distorted chromium(III) complexes in aqueous solutions

Abstract A general method for the analysis of the d-d transition energies observed in the ligand field spectra of chromium(III) complexes with D 4 h or C 4υ symmetry is described and used to derive the crystal field and angular overlap parameters for the complexes of known stereochemistry. Examples are also presented. The spectrum of the diamminetetrakis(isothiocyanato)chromate(III) ammonium in aqueous solution is reported. The spectra of the miscellaneous systems have been studied theoretically using a crystal field model and an angular overlap model.

Coordination behavior of the ligand 1,9-bis(3,5-dimethyl-1-pyrazolyl)-3,7-dithianonane (bddn) towards first-row transition metals. X-ray structure of [Cu(bddn)(H 2O)](BF 4) 2

The synthesis and characterization of the ligand 1,9-bis(3,5-dimethyl-1-pyrazolyl)-3,7-dithianonane (bddn) and its coordination compounds, viz. [M(L)(X) 2] where M is Co 2+, Zn 2+; X is Cl −, Br −, NCS −, and [Cu(L)(H 2O)](BF 4) 2 are described. The X-ray structure of [Cu(bddn)(H 2O)](BF 4) 2 has been determined. The compound crystallizes from ethanol in the monoclinic space group P2 1/ c with unit-cell parameters a=18.508(5), b=9.253(3), c=15.743(5) Å, β=107.91(3)°, V=2565.5 Å 3, D calc=1.57 g/cm 3 for Z=4. The structure was refined to R=0.099 and R w=0.116 for 1841 unique reflections with I>σ( I). The copper(II) ion is coordinated by two pyrazole nitrogen donors, two thioether donors and a water molecule in a trigonal bipyramidal environment, with the two pyrazoles in an unusual cis position. The donor atoms at the axial positions area nitrogen and a sulfur, the equatorial plane donors are nitrogen, sulfur and the oxygen atom. From the ligand field spectra, the infrared patterns and the X-ray powder patterns it was concluded that the structures of the cobalt(II)- and zinc(II)-containing compounds are structurally similar to Zn(bddo)(NCS) 2, a previously reported chain like structure with an MN 2N′ 2 chromophore, in which the ligand S atoms do not bind to the metal ion.