Four-coordinate Structure Research Articles

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N, N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N, N-dimethylformamide (DMF) containing 0.4 M (C 2H 5) 4 NBF 4 as a constant ionic medium at 25°C. The calorimetric data were well explained in terms of the formation of [Mn(ur)] 2+, [Mn(ur) 2] 2+ and [Mn(ur) 4] 2+ for manganese(II), [Ni(ur)] 2+ for nickel(II) and [Zn(ur)] 2+ and [Zn(ur) 2] 2+ for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)] 2+, [Mn(ur) 2] 2+, [Ni(ur)] 2+, [Zn(ur)] 2+ and [Zn(ur) 2] 2+ complexes have a six-coordinate octahedral structure, while the [Mn(ur) 4] 2+ complex has a four-coordinate tetrahedral structure.

Structural and electronic factors in heterolytic cleavage: formation of the Co(I) intermediate in the corrinoid/iron-sulfur protein from Clostridium thermoaceticum.

We have completed the first direct structural characterization of an enzyme-bound four-coordinate Co(I) intermediate, in this case for the corrinoid/iron-sulfur protein (C/Fe-SP) from Clostridium thermoaceticum. Extended X-ray absorption fine structure and X-ray edge spectroscopy of the active Co(I) state of the C/Fe-SP indicates a four-coordinate (distorted) square-planar structure where the best fit gives average Co-N(equatorial) distances of 1.87 +/- 0.01 A, corresponding to 4.2 +/- 0.3 ligands. The X-ray edge spectrum of Co(I) C/Fe-SP contains a moderate intensity 1s-4p + "shake-down" (SD) transition and no 1s-3d peak (where SD transitions are indicative of square-planar geometries). X-ray edge results for the methyl-Co(III) form, reported earlier [Wirt, M. D., Kumar, M., Ragsdale, S. W., & Chance, M. R. (1993) J. Am. Chem. Soc. 115, 2146-2150], are consistent with a base-off methylcobamide structure. The absence of a ligated 5-methoxybenzimidazole base in the methyl-Co(III) state is important since the base-off form is predicted to predispose the Co-C bond toward heterolytic cleavage to form the four-coordinate Co(I) species concurrent with methyl transfer. Additionally, we have examined first-derivative X-ray edge spectra of Co(I) C/Fe-SP, relative to edge spectra of a cobalt foil, as an indicator of effective nuclear charge on cobalt. The Co(I) C/Fe-SP edge position at 7720.5 +/- 0.3 eV is less than, but very close to, the value seen for the corresponding free Co(I) cobalamin.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the stereochemistry of diphenyl diketone monothio-semicarbazone and its transition metal complexes

The stereochemistry and complexation behaviour of diphenyl diketone monothiosemicarbazone (DKTS) with CuII, CoII, NiII, CdII, ZnII, PdII, PtII, RuIII, RhIII and IrIII have been investigated by means of chemical, magnetic and spectral (i.r., Raman, 1H- and 13C-n.m.r. and electronic) studies. The ligand forms complexes of the M(DKTS)2 type with NiII, CuII and CoII having a distorted octahedral geometry. The absence of a v(M—X) band in the i.r. spectra, coupled with their 1:1 electrolytic conductances, suggests that RuIII, RhIII and IrIII form octahedral complexes of the [M(DKTS)2]Cl type. A four-coordinate structure involving bridging halides is proposed for the ZnII, CdII, PdII and PtII complexes, which have relatively low v(M—X) vibration modes.

Steric solvent effect on small and large cations: calorimetric study of halogeno and thiocyanato complexes of beryllium(II) and cadmium(II) in N,N-dimethylacetamide

Solution equilibria of beryllium(II) and cadmium(II) complexes with halide and thiocyanate ions are studied in N,N-dimethylacetamide (DMA) by calorimetry. Mononuclear BeII complexes, [BeX]+ and [BeX2](X = Cl, SCN), and CdII complexes, [CdX]+, [CdX2], [CdX3]– and [CdX4]2–(X = Cl, Br, I, SCN), are found, and their formation constants, enthalpies and entropies are determined. The BeII systems are also studied in N,N-dimethylformamide (DMF). Each of the BeII complexes has very similar thermodynamic quantities in DMA and in DMF, in sharp contrast to first-row transition metal(II) complexes where a marked solvent effect has been observed. In spite of the very small size of the cation, steric hindrance of DMA is absent in the four-coordinate solvation structure of Be2+. ΔH°n and ΔS°n for the CdII complexes in DMA are largely different from those in DMF, which shows the steric solvent effect of DMA, i.e. steric hindrance does exist in the six-coordinate structure of this fairly large cation. When combined, these results offer clear evidence for the octahedral-specific nature of the steric hindrance in metal–DMA interactions.

Synthesis, characterization and structure of cyclopalladated ferrocenylketimines

The reactions of ferrocenylketimines C 5H 5FeC 5H 4C(CH 3)NAr (Ar = a variety of substituted phenyls, 1-naphthyl and 2-naphthyl) with lithium tetrachloropalladate (II) in the presence of sodium acetate in methanol for about 20 h at room temperature and the treatment of the result products with triphenylphosphine lead to the five-membered cyclopalladated derivatives [P dCl{C 5H 5FeC 5H 3C(CH 3)N Ar (PPh 3)]. The structures of these metallocycles have been confirmed by IR and 1H NMR spectroscopies, and further by X-ray crystal structure determination of [P dCl {CH 5FeC 5H 3C(CH 3)N (C 6H 4-4-Cl)} (PPh 3)]. The palladium atom shows the four-coordinate structure typical of palladium complex, and the PdN distance is 2.135 Å. The 1H NMR spectra of [P dCl {C 5H 5FeC 5H 3C(CH 3)N Ar} (PPh 3)] (Ar  C 6H 4-2-Cl and 1-naphthyl) show that both compounds exist as a mixture of two isomers.

Structural Effect of Several Acyclic Neutral Carriers Containing 8-Quinolyloxy Units on the Stability Constants of Their Li+ Complexes in Water-Saturated Nitrobenzene

The stability constants (β1NB(M)/mol-1 dm3) of 1:1 complexes of M+ (=Li+, Na+) with 1,3-bis(8-quinolyloxy)propane (IV), 1,4-bis(8-quinolyloxy)butane (V) and 3,3-bis[(7-methyl-8-quinolyloxy)methyl]oxetane (VI) were determined by ion-transfer polarography in water-saturated nitrobenzene (NB) at 25° C. Their logarithmic values were on the order of VI (4.6)< V (5.7)<IV (7.4) for M=Li and VI (3.9)< V (4.5)<IV (5.7) for M=Na. This order shows that the stability of the Li+ and Na+ complexes significantly increases when the carrier can form a four-coordinate structure similar to that of a tetradentate 14-crown-4 in their complexes. The potentiometric selectivity coefficients (kLiNapot) of IV -VI for Li+ against Na+ were calculated based on the β1NB(M)-values using the equation log kLiNapot=0.70+logβ1NB(Na)/β1NB(Li)], and the results compared with those previously described for other bis(8-quinolyloxy)propane derivatives.

X-ray photoelectron spectroscopy of Al- and B-substituted sodium trisilicate glasses

X-ray photoelectron spectroscopy (XPS) has revealed physical and chemical structure differences between aluminum and boron substituted sodium silicate glasses, Na2O · xR2O3 · (3 − 2x)SiO2, prepared by a melt quench method, where R = Al or B, and x = 0, 0.2, 0.4, 0.6, 0.8, 1. The structure of sodium aluminosilicate (SAS) glasses deduced from the analysis of XPS data is found to agree with the four-coordinated aluminum structure model with Na balancing the local charge. The structure of sodium borosilicate (SBS) glasses is mostly consistent with Bray's model with the need to consider a ‘contending factor’ for Na. Sodium is not fully ionized as often assumed. Its ionicity increases in both SAS and SBS glasses with increasing Al/B substitution. Net charge on atoms according to Pauling's model has been calculated as a guidance in analyzing the XPS spectra.

Synthesis and structural characterization of (2-oxazolinylthienyl)tetraorganotin(IV) compounds

The synthesis and spectroscopic characterization ( 119 mSn Mössbauer and 13C/ 119Sn NMR) of a series of thienyl tetraorganotin compounds, L n SnR 4- n , (L  [2-(4,4-dimethyl-2-oxazolinyl)-3-thienyl]; R  CH 3, n-C 4H 9, c-C 6H 11, C 6H 5, p-CH 3C 6H 4 and p-ClC 6H 4; n = 1, 2) are described. The compounds are essentially four-coordinate structures in the solid state and in solution. An X-ray crystal structure analysis of [2-(4,4-dimethyl-2-oxazolinyl)-3-thienyl]tri( p-tolyl)tin confirms the tetrahedral geometry at tin. The oxazolinyl substituent on the thienyl ring is oriented in such a way that the oxygen atom rather than the nitrogen points towards tin at a non-bonded contact of 2.977(3) Å, thus inducing a slight distortion of the tetrahedral geometry. This finding contrasts with those for LSnPh 2Cl and LSnMe 2(S 2CNMe 2), in which the oxazolinyl nitrogen is intramolecularly coordinated to tin.

Some triphenyltin(IV) complexes containing potentially bidentate, biologically active anionic groups

Triphenyltin(IV) derivatives have been synthesized which contain anions from various biologically active acids. The coordination about the tin atom was investigated by infrared, 119Sn NMR and Mössbauer spectroscopic methods. The triphenyltin cation with S-bonding groups generally acquires a four-coordinated structure. On the other hand, combination with O-bonding groups can produce several structural possibilities: four-coordinate, five-coordinate cis- and trans-trigonal bipyramidal and bridging carboxylate examples being obtained. Some of the higher coordination number species appear to dissociate in solution.

Triphenyltin derivatives of isothiazol-3(2 H)-one 1,1-dioxides. Synthesis, Mössbauer spectra, some fungitoxicity data, and crystal structure of triphenylstannyl 1,2-benziosthiazol-3-(2 H)-one 1,1-dioxide· N,N-dimethylformamide

The syntheses and tin-119m Mössbauer spectroscopic data are reported for two series of stannylimides, 2-triphenylstannyl 1,2-benziosithiazol-3(2 H)-one 1,1-dioxide·L (L = O-donor ligand) and 2-triphenylstannyl 4,5-substituted isothiazol-3(2 H)-one 1,1-dioxides, and for the stannylester, triphenyltin 1,2-benzisothiazol-3(2 H-onyl-2-acetate 1,1-dioxide. The observed quadrupole splitting (QS) values (3.12–3.25 mm s −1) are interpreted in terms of trans-C 3SnNo trigonal bipyramidal structures for the (C 6H 5) 3Sn NC(O)C 6H 4S O 2·L [ L = (C 6H 5) 2C 2CO, (CH 3) 2NCHO, C 9H 7NO, (C 6H 5CH 2) 2SO, (C 6H 5 3PO, (C 6H 5) 3AsO] adducts. A crystal structure determination of the N,N-dimethylformamide adduct confirms the Mössbauer assignment. The ipso-carbons [Sn-C 2.120(4), 2.120(5), 2.122(5) Å] comprise the equatorial girdle of the trigonal bipyramid, the apical positions being occupied by the imido nitrogen [Sn−N 2.242(5) Å] and amido oxygen [Sn–O 2.402(5) Å] atoms. A similar five-coordinate structure is assigned to (C 6H 5) 3Sn NC(O)C(R′)C(R″)S O 2 [Qs 2.95–3.32 mm s −1; R′ = R″ = CH 3; R′ = H, R″ = C 6H 5; = −(CH 2) 4−; R′R″ = −(CH 2) 5−], but for the R′ = CH 3, R″ = C 6H 5 derivative, the lower QS value (2.54 mm s −1) is more consistent with a four-coordinated tetrahedral structure. A trans-C 3SnO 2 trigonal bipyramidal structure for the (C 6H 5) 3SnO 2CCH 2 NC(O)C 6H 4S O 2 stannylester is indicated by its large QS (3.53 mm s −1). Results on fungitoxicity tests on some of the triphenyltin compounds are presented.

Spectroscopic studies of myoglobin at low pH: heme ligation kinetics

On the basis of the characterization of heme structure and ligation in equilibrium, we explore both proximal and distal ligation kinetics of myoglobin below pH 4. Upon photolysis of MbCO, a significant five-coordinate heme population is observed, with an intact iron-histidine bond that persists on the time scale of CO rebinding. Incomplete CO photolysis is attributed to a rapidly exchanging minority population of four-coordinate hemes, which leads to fast (greater than 10(10) s-1) geminate recombination. The possible relevance of such a mechanism at pH 7 is also noted. Using a novel experimental protocol, we observe the resonance Raman spectrum of partially photolyzed MbCO as a function of continuous wave illumination time (tau). Under extended illumination (tau approximately 35 ms at pH 3.4), there is a loss of intensity in the nu 4 region of the Raman spectrum and the iron-histidine mode is bleached from the spectrum of the five-coordinate photoproduct. In the Fe-CO stretching region of the CO-bound fraction, the intensity of the 526-cm-1 mode increases with tau at the expense of the 491-cm-1 mode. These changes are interpreted as being due to replacement of the proximal histidine ligand under continuous illumination. Complete relaxation to the pure four-coordinate deoxy heme structure observed in equilibrium is not observed even as tau----infinity, presumably since CO rebinding leads to acidification of the iron and its complexation with histidine. We propose a kinetic model to account for our results and discuss the implications for previous low-pH kinetics measurements.

Ion chemistry of phosphorus in hydrocarbon flames: Part II. Positive Ion Formation

Premixed methane/oxygen flames at atmospheric pressure of both fuel-rich (FR) and fuel-lean (FL; i.e. oxygen-rich) composition were doped with small amounts (< 0.1 mol%) of volatile phosphorus alkyl triesters. The phosphorus positive ions (cations) produced by chemical ionization reactions were observed by sampling the flame through a nozzle into a mass spectrometer. This study follows on from Part I in which the phosphorus negative ions (anions) were similarly investigated. About a dozen phosphorus cations were observed in each flame below 160 u, many of them common to both flames. The cations can be represented by five series. The first involves ions of the type (RO) 4- n P(OH) + n with n = 0–4 (FR, R = CH 3) or n = 2–4(FL, R = CH 2H 5). Evidence was obtained for a methyl cation transfer reaction. The remaining four series amount to the hydrates PO + n · xH 2O with n = 1–4; x has various values for each series in each flame in the range 0–3. However, many of these “hydrates” have the general form PO a (OH) b (O 2) c (H 2O) + d involving coordinate bond formation of O 2 and H 2O with the central P atom. Virtually all the high-mass ions appear to have four-coordinate tetrahedral structures. The phosphorus cation formation chemistry is discussed in detail involving three-body association, nucleophilic displacement (S N2) and proton transfer reactions. Finally, some points of comparison are made between the cations and the phosphorus anions presented in Part I.

A Novel Topological Compression Mechanism in a Covalent Liquid

Monte Carlo simulations of tetrahedrally bonded SiO(2) liquid show that pressure induces large changes in the topology of its four-coordinated framework structure but leaves the average properties of local coordination environments virtually unchanged. Ring statistics are used to describe the liquid's topology; the observed changes paradoxically indicate that the liquid compresses primarily by increasing the size of its rings. A theory for the effects of ring formation on density, which also explains the density of crystalline tectosilicates, accounts for the compression of the liquid.

Synthesis and Structural Information on Mercury(II) Chloride Complexes with Some Mono-Ortho Substituted Medially Metallized Type Azo Dyes

Abstract The preparation of 1:2 and 1:1 mercury(II) chloride complexes with arylazo ligands is described. These compounds are freely soluble in methanol in they behave as non-electrolytes. Based on molar conductance, 1H n.m.r., electronic spectra and i.r. spectral features down to 200cm−1, complexes of arylazo-2-naphthol(L1H) and arylazopyridines (L3−L6) are considered as neutral, four-coordinated tetrahedral structures while complexes of arylazo-2-carboxylic acid (L2H) appear to be neutral, three-coordinated around mercury(II).

D-Glucose adducts with zinc-group metal ions. Synthesis, and spectroscopic and structural characterization of Zn(II), Cd(II), and Hg(II) complexes with d-glucose, and the effects of metal-ion binding on the sugar anomeric structures

The interaction of the zinc-group metal halide salts in solution with d-glucose has been investigated. Solid adducts of the type M( d-glucose)X 2· nH 2O, where M = Zn(II), Cd(II), or Hg(II); X = Cl − or Br −; and n = 4 or 2, were isolated and characterized by f.t.-i.r. and n.m.r. spectroscopy, and by molar conductivity measurements. The Zn(II)- and Cd(II)-glucose adducts appear structurally similar, binding to one d-glucose molecule, possibly through the 1-OH and 2-OH groups as well as to four H 2O molecules, forming a six-coordinate metal cation. The Hg(II) ion may be bonded to two sugar molecules (unidentately) and to two H 2O molecules, resulting in a four-coordinate structure around mercury. The binding of Zn(II) and Cd(II) is via the α anomer of d-glucose. The possibility cannot be excluded that the Hg(II) ion binds to both the α and β anomers.

The reaction of [PtCl 4] 2− with 1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane: complete product selectivity via non-coordinating anions and isolation of two intermediates

The reaction of [PtCl 4] 2− with 1,1,4,7,10,10- hexaphenyl-1,4,7,10-tetraphosphadecane (P 4) leads to four different products due to the formation of intermediates and the presence of two different diastereomers of P 4. The four complexes can be separated using non-coordinating anions. [PtCl(P 4)]-(BF 4) ( 1), [PtCl(P 4)](BPh 4) ( 2), chiral. [Pt(P 4)]- (BPh 4) 2 ( 3) and meso-[Pt(P 4)](BPh 4) 2 ( 4) have been characterized by elemental analyses, 195Pt and 31P NMR spectroscopy, and in one case ( 3) by a preliminary X-ray diffraction analysis. In the five-coordinate complex 1 P 4 has a tetrahedral arrangement. 2 is also five-coordinate, the chloride occupying the apical and P 4 the four basal positions of a square pyramid. 3 and 4 have four-coordinate square-planar structures where the X-ray structure of 3 shows it to be the chiral form of the two possible diastereomers. 4 is therefore supposed to be the meso form. A steric effect as a possible reason for the observed diastereoselective action of Na- (BPh 4) is discussed.

Synthesis and spectra of Co(salen) derivatives containing pendant groups and their dioxygen adducts. Pendant chain length and coordinating ability

Five Co(salen) derivatives, Co(sal-moen), Co(sal-motn), Co(sal-ipstn), Co(sal-eatn) and Co(sal-batn) containing the (CH 2) 2OCH 3, (CH 2) 3OCH 3, (CH 2) 3SCH(CH 3) 2, (CH 2) 3N(C 2H 5)a and (CH 2) 3N(n-C 4H 9) 2 as the pendant groups, respectively, were newly synthesized. Electronic spectra obtained at room temperature show that all the complexes are free from pendant coordination. On the other hand, ESR spectra in frozen CH 2Cl 2 at liquid nitrogen temperature indicate that Co(salmotn) and Co(sal-batn) retain the four-coordinate structure while Co(sal-moen), Co(sal-ipstn) and Co(sal-eatn) exist as a mixture of the four- and five-coordinate species. Upon oxygenation at −90°C, all the complexes form dioxygen adducts in which the pendant group occupies the axial position trans to the dioxygen. Resonance Raman spectra exhibit the ν(O 2) and ν(CoO 2) at 1150–1142 and 538–522 cm −1, respectively, which are typical of six-coordinate, ‘base-bound’ dioxygen adducts. These results suggest that pendant coordination is possible regardless of the nature of the donor atom as long as the latter is bonded to the Co(salen) core via two or three methylene bridges.

A Calorimetric Study of Ternary Zinc(II) Complexes with Chloride Ions and 2,2′-Bipyridyl in N,N-Dimethylformamide

Abstract Formation equilibria of ternary zinc(II) complexes with chloride ions and 2,2′-bipyridyl (bpy) have been calorimetrically studied in N,N-dimethylformamide (DMF) containing 0.4 mol dm−3 (C2H5)4NClO4 as a constant ionic medium at 25 °C. Formation of binary (2,2′-bipyridyl)zinc(II) complexes has also been explored. The calorimetric data were satisfactorily explained in terms of formation of the ternary [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes together with the binary [Zn(bpy)n]2+ (n=1–3) ones, and their formation constants and enthalpies were determined. The formation of the ternary [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes is not so favorable in DMF. It is suggested that both [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes have the four-coordinate tetrahedral structure in DMF.

Stereochemical Properties of Copper(II) Complexes of (RS)-3-Aminohexahydroazepine: Crystal and Molecular Structures of [(R)-3-Aminohexahydroazepine][(S)-3-aminohexahydroazepine]copper(II) Diperchlorate, [Cu(R-ahaz)(S-ahaz)](ClO4)2 and Related Complexes

Abstract Orange-red copper(II) complexes of (RS)-3-aminohexahydroazepine (=RS-ahaz), Cu(RS-ahaz)2X2·nH2O (X−=ClO4−, BF4−, NO3−, Br−, I−) were prepared, and the molecular structures of complex 1 (X−=ClO4−; n=0) and complex 2 (X−=Br−; n=2) were determined by the single-crystal X-ray diffraction method. The complex 1 has centrosymmetry, and the complex cation in 1 involves a pair of R- and S-ahaz (R- and S-ahaz refer to (R)-and (S)-3-aminohexahydroazepine) and takes a strict four-coordination geometry, so that 1 is formulated as [Cu(R-ahaz)(S-ahaz)](ClO4)2. The complex cation in 2 resembles closely that of 1, and 2 can be represented as [Cu(R-ahaz)(S-ahaz)]Br2·2H2O. The other orange-red complexes of RS-ahaz (X−=BF4−, NO3−, I−) were concluded to take similar strict four-coordinated structures. Blue-violet hetero-anion complexes Cu(RS-ahaz)2X(ClO4) were obtained from complex 1 and LiX (X−=Cl−, Br−). The crystal structure determination of Cu(RS-ahaz)2Br(ClO4) (=complex 3) revealed that 3 involves a pair of enantiomeric five-coordinated cations, [CuBr(R-ahaz)2]+ and [CuBr(S-ahaz)2]+, in the single crystal, whereby the ligand exchange which proceeds during the transformation from 1 to 3 is indicated.

A spectral study of transition-metal complexes on a chelating ion-exchange resin containing aminophosphonic acid groups

The coordination mode of a commercial chelating ion-exchange resin, ES 467, containing aminomethylphosphonic acid groups anchored on a macroporous styrenedivinylbenzene copolymer, with several metal ions, such as chromium(III), cobalt(II), nickel(II), copper(II) and zinc(II) has been studied with the aid of IR, ligand field and ESR spectra. The chelating group of ES 467, aminomethylphosphonic acid, appears to bind different metal ions mainly through oxygen atoms of the phosphonic acid group, though, in the case of those species containing low-loading of metal ions, the secondary amine nitrogen atom also appears to take part in coordination. Most of the metal ions studied seem to be present as six-coordinated species in the polymeric matrix, whereas cobalt(II) species show electronic spectra which are consistent with the presence of both four-coordinated (tetrahedral) and six-coordinated (octahedral) structures of these species. The distribution coefficients for cobalt(II), nickel(II), copper(II) and zinc(II) have been determined and it appears that the resin ES 467 binds copper(II) ions selectively. An attempt has been made to find a possible relationship between the selectivity of the chelating resin and the stereochemistry of the adsorbed metal ions.