Secondary Amine Nitrogen Atoms Research Articles

Synthesis and Characterization of Homo- and Heterodinuclear Complexes Containing the N3M(μ2-SR)3MN3 Core (M = Fe, Co, Ni)

A novel amine-thiolate ligand, H33·6HCl (N,N‘,N‘‘-tris-[2-thio-3-aminomethyl-5-tert-butylbenzyl]-1,1,1-tris(aminomethyl)ethane), has been synthesized and used in the preparation of dinuclear complexes of Fe, Co, and Ni. The nonadentate N6S3 ligand H33 is formally derived from the symmetric tridentate N2S ligand H11 (2,6-bis(aminomethyl)-4-tert-butylthiophenol). It provides two dissimilar octahedral N3S3 and N‘3S3 coordination sites to give complexes with a central N3M(μ2-SR)3MN‘3 core structure (N and N‘ denote primary and secondary amine nitrogen atoms, respectively). The complexes of H33 exist as dinuclear [MII2(3)]+, [MIIIMII(3)]2+, or [MIII2(3)]3+ species which are all accessible by chemical or electrochemical reduction/oxidation. The following complexes were isolated as microcrystalline solids: [CoIII2(3)][ClO4]3 (4b), [NiIIINiII(3)][BPh4]2 (5b), and [FeIIIFeII(3)][BPh4]2 (6b). The chemical and physicochemical properties of the respective species are very similar to those of Fe, Co, and Ni complexes of H11, [M2(1)3]n+ (M = Co, n = 3, (4a); M = Ni, n = 2 (5a); M = Fe, n = 2 (6a)), and support the formulation of 4b−6b as discrete dinuclear species with a central N3M(μ2-SR)3MN‘3 core. NMR spectra of diamagnetic cobalt complexes 4a and 4b reveal the complexes to be C3h and C3 symmetric, respectively, in the solution state. The crystal structure determination of [CoIII2(1)3][Fe(CN)6]·7MeOH·3H2O (4c) (monoclinic, space group C2/c, a = 28.037(2) Å, b = 17.861(1) Å, c = 25.727(2) Å, β = 90.24(1)°, and Z = 8) reveals 4c to consist of dinuclear [CoIII2(1)3]3+ trications featuring two fac-octahedral N3CoIII(SR)3 units bridged at the thiolate sulfur atoms. Compound 4c represents the first structurally characterized MIII2 complex of H11. The ability of H33 to form heterodinuclear complexes is demonstrated with the synthesis of [CoIIINiII(3)][BPh4]2 (7) and its linkage isomer [NiIICoIII(3)][BPh4]2 (8). All complexes undergo two electrochemically and chemically reversible one-electron-transfer reactions which convert the respective [M2(3)]n+ species. For MIII2/MIIIMII (E11/2) and MIIIMII/MII2 (E21/2): −0.40 V, −0.84 V (M = Co), +0.49 V, +0.05 V (M = Ni), +0.21 V, −0.33 V (M = Fe) vs SCE. Heterodinuclear complexes 7 and 8 also give rise to two consecutive one-electron-transfer processes at E11/2 (NiIII/II) and E21/2 (CoIII/II): +0.55 V, −0.71 V (for 7) and +0.60 V, −0.86 V (for 8), respectively. Comparison of the electrochemical properties of [CoIIINiII(3)]2+ and [NiIIINiII(3)]2+ reveals the NiIII/II redox potential in the dinuclear complexes to be influenced by the oxidation state of the adjacent metal ion. At 77 K the mixed-valent NiIIINiII (S = 3/2 spin ground states) and FeIIIFeII complexes (S = 1/2 spin ground states) exhibit localized and delocalized valencies, respectively, as indicated by UV−vis, EPR, and 57Fe Mössbauer spectroscopy.

Reactions at the N2Ni(μ2-SR)2NiN2 Core in Dinuclear Nickel(II) Amine-Thiolate Complexes

A discrete dinickel complex with a central N2NiII(μ2-SR)2NiIIN2 core has been synthesized and investigated in the context of ligand binding and oxidation state changes. Reaction of the hexadentate amine-thiolate ligand N,N′-bis-[2-thio-3-aminomethyl-5-tert-butylbenzyl]propane-1,3-diamine (8) with Ni(ClO4)2 · 6 H2O in methanol affords [NiII28][ClO4]2 · 3 CH3OH (9), the structure of which has been determined by X-ray crystallography. Complex 9 contains a central N2Ni(μ2-SR)2NiN2 core with two approximately planar cis-N2S2Ni coordination polyhedra bridged at the thiolate sulfur atoms. The cis-N2S2Ni units differ in that one nickel atom forms a six-membered chelate ring with the two secondary amine nitrogen atoms of 8 whereas the other nickel atom is bound to the remaining primary nitrogen atoms. Complex 9 binds a variety of substrates. Binding of anions to the N2Ni(μ2-SR)2NiN2 core in 9 occurs selectively at the Ni atom bound to the secondary nitrogen atoms because of a slightly weaker ligand-field strength. This is demonstrated by X-ray structure determination of the isothiocyanate complex [NiII28(NCS)2] · MeOH (10) formed by the reaction of 9 with 2 equiv. of KSCN in methanol. Complex 10 is the first example of a complex with adjacent octahedral cis-N4S2Ni and planar cis-N2S2Ni sites. The overall dinuclear structure of the parent complex 9 is retained in 10, except for trans-axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inversion of configuration at both secondary amine nitrogen atoms. In DMF solution both complexes undergo two successive reductions at potentials of –0.95 V and –1.53 V vs SCE, assigned to the formation of mixed-valent [NiINiII8]1+ and [NiI28]0 species, respectively. The similar electrochemical properties of 9 and 10 suggest that the trans-axially bound isothiocyanate ions in 10 are replaced by DMF molecules in DMF solution. Upon reduction, these solvent molecules decoordinate to produce an unsolvated [NiINiII8]1+ species with two planar N2S2Ni units.

Capillary electrophoresis, potentiometric and laser excited luminescence studies of lanthanide(III) complexes of 1,7-dicarboxymethyl-1,4,7,10-tetraazacyclododecane (DO2A) †

The protonation constants of the ligand 1,7-dicarboxymethyl-1,4,7,10-tetraazacyclododecane (DO2A) were re-determined by the potentiometric pH titration method (log K 10.94, 9.55, 3.85, 2.55) and the macrocycle ring protonation sites have also been confirmed by NMR techniques to be the secondary amine nitrogen atoms. The stability constants of calcium(II) and all trivalent lanthanide (Ln3+) metal complexes of DO2A (Ca2+, log KML 7.16; Ln3+, log KML 10.94–13.31) were determined by the potentiometric pH titration and capillary electrophoresis methods, respectively. In general, the stabilities of the Ln(DO2A)+ complexes increase with increasing atomic number for the lighter lanthanides (La3+–Sm3+) and remain relatively unchanged for the heavier lanthanides (Eu3+–Lu3+). Laser-excited spectroscopy of the 7Fo → 5Do transition of Eu3+ is used to study the aqueous Eu3+–DO2A complex system. At low pH (e.g. pH 5–6) Eu3+ forms a 1∶1 species with the ligand DO2A, presumably Eu(DO2A)(H2O)q+, where q is the number of inner-sphere coordinated water molecules. As the solution pH increases the hydrolysis product, Eu(DO2A)(OH)(H2O)q – 1, is formed. Lifetime measurements of each species in H2O and D2O allow the determination of the corresponding number of inner-sphere coordinated water molecules to be 3.0 and 2.6, consistent with the proposed structures (i.e.q = 3). The first hydrolysis constant (pKh) is estimated to be 8.1 ± 0.3.

Vanadium(V) Complexes with Flexible and Hydrolytically Stable Amine Alcohol Ligands and their isomerization in solution: Models for the interaction of Vanadium(V) with biogenic ligands

AbstractThe hydrolytically stable trivalent, pentadentate amine alcohol ligands 1,1‐bis(2‐hydroxyethyl)‐4‐(2‐hydroxy‐5‐R‐benzyl)‐1,4‐diazabutane 2 (H3hebab–R; a: R = H, b: R = OMe, c: R = Br, d: R = NO2) react with ammonium metavanadate to form the oxovanadium(V) complexes [VO(hebab–R)] 4, which have been characterized by 1H, 13C, and 51V NMR, vibrational (IR, Raman, and resonance Raman) and electronic spectroscopy. According the high flexibility of the ligand systems the complexes 4 possess two different possible structures in solution. These two isomers differ in the ligand arrangement: fac‐4 possesses a facial configuration of the phenolate oxygen and the two amine nitrogen donors with the oxo group trans to the tertiary amine nitrogen atom, whereas mer‐4 is characterized by a meridional configuration of the phenolate oxygen and the two amine nitrogen donors with the oxo group trans to the secondary amine nitrogen atom. The two isomers are related by an isomerization equilibrium proceeding via a rotation about a pseudo C3 axis of the octahedral coordination environment. This isomerization mechanism seems to be of general importance, since it can also account for the solution structures of oxovanadium(V), cis‐dioxovanadium(V) and cis‐dioxomolybdenum(VI) complexes of flexible high‐denticity ligand systems. The electronic influence of the para substituent at the phenolate on the isomerization reaction has been investigated by 51V NMR spectroscopy. The thermodynamic parameters determined from the variable‐temperature 51V NMR data show the fac‐isomers to be more stable in all cases. Although the smallest ΔH° is observed for the methoxy substituted derivative 4b, the X‐ray crystal structure analysis shows that even in this case solely the fac‐isomer is present in the solid state. For 4b the 1H and 13C NMR data of both isomers can be observed and assigned. The data reveal a pronounced dependence of the coordination induced shift for the relevant resonances on the relative orientation of the chelate rings with respect to the oxo group at the vanadium center, leading to characteristic resonance patterns. Additional information on the electronic structure of the complexes 4 and the analogous Schiff base derivatives [VO(sabhea–R)] 3 (H3sabhea–R = N‐(5‐R‐salicylidene)‐2‐(bis(2‐hydroxyethyl)‐amino)ethylamine; a: R = H, b: R = OMe, c: R = Br, d: R = NO2) has been derived from cyclic voltammetry and density functional calculations. The methanolysis reaction of the complexes 4 has been studied by 51V NMR spectroscopy. A penta‐coordinate intermediate has been observed, which indicates the semilabile character of the diethanolamine fragment of the ligand systems 2 in the corresponding oxovanadium(V) complexes.

Intermediate Products of the Reaction of (4,4,9,9-Tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone)nickel(II) With Butane-2,3-dione; the Structure of cis-Aqua(3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexadeca-1(16),4,6-tien-3-Ol)nickel(II) Perchlorate Trihydrate

Intermediate products have been isolated from the reaction of (4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone )nickel(II) perchlorate with butane-2,3-dione which finally yields the macrocyclic product (3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexa-deca-2,4,6,16-tetraene)nickel(II) perchlorate , [Ni( omht )] (ClO4)2. An initial violet product is assigned a structure with the macrocyclic ligand 3-acetyl-3,6,8,8,13,13,15-heptamethyl-1,2,4,5,9,12-hexaazacyclopentadeca-5,15-diene. In water this converts into an equilibrium mixture of the tautomeric cations blue cis-aqua(3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexadeca-1(16),4,6-trien-3-ol)nickel(II), cis-[Ni(L2)(H2O)]2+, and orange (3,6,8,- 8,13,13-hexamethyl-4,5,9,12-tetraazahexadeca-3,5-diene-2,15-dione 15-hydrazone)nickel(II), [Ni(L3)]2+. The rates at 25°C of the forward and reverse reactions of this tautomerism, and of the slower conversion of the equilibrium mixture to [Ni( omht )](ClO4)2, are reported. The structure of cis -[Ni(L2)(H2O)](ClO4)2.3H2O has been determined by X-ray diffractometry (monoclinic, space group P21/n, a 9.694(8), b 19.218(14), c 16.652(9) Ǻ, β 94.88(1)°, R 0.079 for 3254 reflections). This has NiII in octahedral coordination by secondary amine nitrogen atoms 10 and 13, hydrazone nitrogen atoms 1 and 6, and the carbinolamine oxygen substituent at position 3 of the pentadentate macrocyclic ligand L2, with a water molecule coordinated cis to the hydroxy group. Compounds of the tautomeric cations [Ni(L2)]2+ and [Ni(L3)]2+ with coordinated thiocyanate, azide, nitrite, oxalate and acetate are described.

Novel routes to functionalized cyclam-like macrocycles

Abstract

Amides and sulfonamides: efficient molecular padlocks for the template synthesis of azacyclam (1,3,5,8,12-pentaazacyclotetradecane) macrocycles

Amides and sulfonamides, both aliphatic and aromatic, acted as efficient locking fragments, in the presence of formaldehyde and base (triethylamine), in closing the open-chain tetramine 1,9-diamino-3,7-diazanonane around labile metal centres prone to a square type of co-ordination, i.e. NiII and CuII, to give a pentaazamacrocyclic complex of the azacyclam family. The product of the copper(II) template reaction involving methanesulfonamide as a locking fragment (3-methanesulfonyl-1,3,5,8,12-pentaazacyclo-tetradecane)dinitratocopper(II), was obtained in crystalline form and its crystal and molecular structure determined from single-crystal X-ray diffraction data, collected with the use of Cu-Kα radiation: trigonal, space group R3c, a=b=c= 14.997(3)Å, α=β=γ= 98.48(2)°, Z= 6. Only the four secondary amine nitrogen atoms of the macrocycle are bound to the CuII, giving a regular square stereochemistry. The tertiary nitrogen atom N(1), which presents distinct sp2 structural features, is not involved in the co-ordination. The axial positions of the elongated octahedron are occupied by oxygen atoms of the nitrate ions. A kinetic investigation was carried out on the copper(II) template reactions involving diprotic acids as locking fragments, including amides, amines and carbon acids, such as nitroethane and diethyl malonate: for the systems investigated the rate of the template reaction seems to be related to the strength of the diprotic acid. This suggests that the monodeprotonated form of the acid is present in the rate-determining step of the cyclisation process.

Komplexe 17-gliedriger Dibenzo-Makrocyclen mit N3O2- bzw. N3S2-Donorzentren Strukturen von [Zn(′N3O2′)Cl]2ZnCl4 und [Hg(′N3S2′)Br2] / Complexes of 17-Membered Dibenzo Macrocycles with N3O2 or N3S2 Donor Sets Crystal and Molecular Structures of [Zn(′N3O2′)Cl]2ZnCl4 and [Hg(′N3S2′)Br2

The macrocyclic complexes [Zn(′N3O2')Cl]2ZnCl4 (1) und [Hg(′N3S2')Br2] (2) have been prepared and their crystal structures determined. Zn(II) is incorporated into the macrocyclic cavity of the ′N3O2′ ligand and primarly coordinated to the three nitrogen donors of the macrocycle and to a chloride ion. Weaker interactions occur with the oxygen donors of the macrocycle. The Zn—O distances are 296,4(5) and 322,4(6) pm. In complex 2 Hg(II) lies outside the macrocyclic cavity. The donor set comprises two secondary amine nitrogen atoms and a thioether sulfur atom of the macrocycle, and two bromide anions. The coordination polyhedron can be described as a trigonal bipyramid. The conformational behaviour of the ′N3O2′ and the ′N3S2′ ligands within these and other complexes is discussed. ′N3O2′ and ′N3S2′ are 17-membered dibenzo macrocycles. Crystal data for [Zn(′N3O2')Cl]2ZnCl4 (1): monoclinic, space group C2/c, a = 2864(4), b = 951.0(2), c = 1986(4) pm, β = 118.5(1)°, Z = 4, 2499 reflections, R = 0.0581; [Hg(′N3S2′)Br2] (2): monoclinic, space group P21/c, a = 887.0(2), b = 1307.6(3), c = 2002.3(4) pm, β = 94.13(3)°, Z = 4,3123 reflections, R = 0.072.

Metal-ion selectivity by macrocyclic ligands. Part 2. The interaction of Zn II , Cd II and Hg II with pyridinyl-derived N3O2 macrocycles; X-Ray structures of one zinc and two cadmium endomacrocyclic complexes and of one zinc and one mercury exomacrocyclic complex

The interaction of ZnII, CdII and HgII with the macrocycles L1 and L2, each containing an N3O2-donor set, has been investigated. Conductometric titration of the 1:1 complexes of ZnII and CdII with chloride in each case indicated the sequential formation of a 1:1 electrolyte of the type [ML(Cl)]+ and a 2:1 electrolyte of the type [MLCl2] in each case. Proton NMR titration of the ligands with M(O2CMe)2 in CD3OD gave evidence for the formation of 1:1 and 1:2 (metal : ligand) species. The stability constants of the complexes have been determined in 95% methanol. The X-ray crystal structures of the 1:1 complexes [ZnL1I2]·H2O, [ZnL1(NO3)]NO3, [CdL1(NO3)(MeOH)]NO3, [CdL2-(ClO4)(MeCN)]ClO4 and [HgL1I2] have been determined. The metal atoms in [ZnL1I2]·H2O and [HgL1I2] are four-co-ordinated in a tetrahedral geometry and lie outside the macrocyclic cavity. The donor set in each molecule comprises the two secondary amine nitrogen atoms from the macrocycle and the two iodide anions. The complex [ZnL1(NO3)]NO3 has all donors of the macrocycle co-ordinated with one oxygen from a nitrate anion occupying the sixth site to yield an approximately trigonal-prismatic geometry. The structure of [CdL1(NO3)(MeOH)]NO3 shows that the metal is seven-co-ordinated in an approximately pentagonal-bipyramidal environment consisting of the full donor set of the macrocycle together with one oxygen each from a nitrate anion and a methanol of solvation. The structure of [CdL2(ClO4)(MeCN)]ClO4 shows that the metal has a similar co-ordination environment consisting of the full donor set of the macrocycle together with an oxygen from a perchlorate anion and a nitrogen from acetonitrile of solvation.

Crystal and molecular structure and solution behaviour of low-spin (3-methyl-1,3,5,8,12-pentaazacyclotetradecane)κ4N1,N5,N8,N12)nickel(II) diperchlorate

Template reaction of 3,7-diazanonane-1,9-diamine, formaldehyde and methylamine, in the presence of Ni(CIO4)2, gives the pentaazamacrocyclic low-spin complex [Ni(azacyclam)][CIO4]2(azacyclam = 3-methyl-1,3,5,8,12-pentaazacyclotetradecane), whose crystal and molecular structure was determined from single-crystal X-ray diffraction data collected with the use of Cu-Kα radiation: space group P212121 with a= 15.967(3), b= 13.497(3), c= 8.737(2)A, α=β=γ= 90°, Z= 4 (R= 0.0705). Only the four secondary amine nitrogen atoms of azacyclam are bound to the metal, according to a regular square-planar stereochemistry, the lone pair of the tertiary nitrogen atom, N(1), being exposed. In particular, the N(1)C3 group is flattened, probably due to a long-range electrostatic interaction between N(1) and the metal. As a consequence, N(1) displays a very small affinity towards aqueous H+(pKa < 2). The [Ni(azacyclam)]2+ complex in aqueous solution displays the high spin–low spin (blue-to-yellow) interconversion, typical of complexes of cyclam. However, in contrast, addition of HCI favours formation of the high-spin form. This unusual behaviour is ascribed to protonation of the N(1) atom, at acid concentrations of 0.5–1.0 mol dm–3, and to axial co-ordination of a hydrogen-bonded chloride ion. Addition of HCIO4 first favours formation of the high-spin species, then that of the low-spin complex: in this case, the hydrogen-bond-facilitated axial co-ordination of a water molecule is hypothesized.

Structural investigation of the Cu(II) chelate of N-phosphonomethylglycine. X-ray crystal structure of Cu(II) [O 2CCH 2NHCH 2PO 3]·Na(H 2O) 3.5

The structure of the metal chelate formed between Cu(II) and N-phosphonomethylglycine (PMG) has been determined by single crystal X-ray diffraction methods. The Cu(II) cation is five-coordinate with donor atoms in a distorted square pyramidal geometry for which the basal plane involves a tridentate combination of the carboxylate oxygen, one of the phosphonate oxygen atoms and the monoprotonated secondary amine nitrogen atom to form two adjacent chelate rings, together with a second phosphonate oxygen atom from an adjacent ligand. The complex is capped and further extended by coordination to one of the basal phosphonate oxygen atoms of yet another adjacent ligand. The phosphonate group of the ligand bridges between three Cu(II) centers through a monodentate O2 and a bidentate O1. Each Cu(II) cation is coordinated by all ligand donor atoms, carboxylate oxygen, nitrogen and phosphonate oxygen, in addition to the two bridging phosphonate oxygens of ligands which are primarily associated with adjacent chelate molecules. The Cu(II) complex is monoclinic, space group C2, with cell parameters a = 21.980(2), b = 4.779(2), c = 10.017(2) Å, β = 93.86(1)°, V= 1049.9(4) Å 3 and Z = 4. The structure was solved by direct methods and refined by a modification of direct difference and least-squares techniques to R = 0.072 with 715 independent reflections, I>3σ( I), and 62 variables.

Structure and Racemization of Optically Active mer-(3-Azapentane-1,5-diamine or 3-methyl-3-azapentane-1,5-diamine)(ethylenediamine-N-acetato)cobalt(III) Complexes

Abstract The crystal structure of (−)500CD-mer-[Co(edma)(dien)]Br2·2/3CH3OH·2/3H2O was determined by the X-ray diffraction method. The crystal is triclinic, space group P1, a=13.824(8), b=13.814(8), c=8.055(3) Å, α=101.18(6), β=101.17(6), γ=116.32(5)°, and Z=3. All of the crystallographically independent complex cations, in which the terdentate ligands coordinate meridionally, have a δ spiral configuration, and the asymmetric nitrogen donor atoms of the edma ligands take an S configuration. The racemization reactions due to the inversion at the secondary amine nitrogen atom of the edma ligand in (−)500CD-mer-[Co(edma)(dien)]2+ and (−)514CD-mer-[Co(edma)(mdien)]2+ were studied at 20–35 °C in the pH range of 6.10–7.24. The rate law for both complexes was described as R=k[OH−][complex]. The activation parameters at 30.0 °C were ΔH\eweq of 94.9 kJ mol−1 and ΔS\eweq of 126 J K−1 mol−1 for the dien complex and ΔH\eweq of 73.8 kJ mol−1 and ΔS\eweq of 62.0 J K−1 mol−1 for the mdien complex.

Studies on cobalt(III) complexes with ( R,S)-8-amino-2-methyl-3,6-diazaoctanoate ion. II. Determination of absolute configuration of mixed complexes with the ( S)-alaninate ligand

Trans(O) and β- mer(N) cis(O) cobalt(III) complexes with ( R,S)-8-amino-2-methyl-3,6-diazaoctanoate ion. (abbreviated as ( R,S)-amda and ( S)-alaniate ion ( S-ala) were prepared, subjected to cation exchange chromatography, and characterized by means of visible absorption, CD, and 1H-NMR spectroscopy. The five optically active diastereoisomers chromatography, and their absolute configurations were assigned in the order of elution to Δ S R (3 S,6 R), Λ S S (3 R,6 S), Δ S S (3 S,6 S), Δ S S (3 S,6 R) and Λ S R (3 R,6 S) diastereoisomers. Here the subscripts R or S and superscript S designate the absolute configurations of the ligands ( R,S)-amda and S-ala, respectively, and the configuration of the secondary amine nitrogen atom (sec-3N and sec-6N in the ( R,S)-amda) is designated as (3 S,6 R) or (3 R,6 S). On the other hand, a sample of the β- mer(N) cis(O) form which was shown to be a mixture of diastereoisomers of (Δ S S (3 S,6 R) + Λ S R (3 R,6 S))-[Co((S)-ala)(( R,S)-amda)]ClO 4, could not so far be separated into components by ion-exchange chromatography.

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.

Crystal and molecular structure of [N N′-(3,3′-dipropylamine)- bis(salicylideneaminato)monoacetate]cobalt(III) complex

The crystal and molecular structure of [N,N′-(3,3′-dipropylamine)bis(salicyclideneaminato)-monoacetate]cobalt(III) complex has been determined by a three-dimensional X-ray diffraction study. In the complex, the cobalt ion has an octahedral coordination environment with cis-geometry for the two salicyclideneaminato moieties. An oxygen atom of the acetate ion is coordinated to cobalt ion and another oxygen atom is hydrogen-bonded to the secondary amine nitrogen atom.

Synthesis of some pentagonal-bipyramidal complexes of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II) with a heptadentate Schiff-base ligand and the crystal and molecular structures of a copper(II) complex

Complexes of the type [ML]X2.xH2O, where M is a divalent metal ion (Mn, Fe, Co, Ni, CU, Zn), X = ClO4- or BPh4-, x= 0 or 1, and L is a potentially heptadentate Schiff base derived from the condensation of one molecule of 2,6-diacetylpyridine with two molecules of diethylenetriamine, are reported. The complexes were prepared by metal exchange from corresponding alkaline-earth metal complexes. By means of a single-crystal X-ray analysis of [CuL][ClO4]2, comparisons of X-ray powder patterns, and various physical properties it is shown that the complexes have a pentagonal-bipyramidal structure in the solid state and also, nickel(II) complexes excepted, in acetonitrile solution. Crystals of [CuL][ClO4]2, are monoclinic, with a= 12.18(1), b= 13.78(1), c= 14.92(1)A, β= 98.3(1)°, Z= 4, space group P21/n. 1 486 Reflections above background have been measured by diffractometer and refined by full-matrix least squares to R 0.079. The three nitrogen atoms of the trimethine group together with the two secondary amine nitrogen atoms define the equatorial plane of a distorted pentagonal bipyramid, the primary amine nitrogen atoms occupying the axial positions. The Cu–Nax. bonds [1.993(19), 1.997(20)A] are notably shorter than the Cu–Neq. bonds (average 2.356 A). The transition-metal complexes are all high spin. Electronic spectra are reported, as well as the e.s.r. spectrum of [CuL][BPh4]2.

Conformations of GABA analogues. I: Crystal and molecular structure of guanidinoacetic acid

The crystal and molecular structure of guanidinoacetic acid has been determined by single-crystal X-ray diffraction techniques. The crystals are monoclinic, space groupP21/c, witha = 4.942(3),b = 6.010(3),c = 21.911(14) A, β = 128.60(4) °, andZ = 4. The structure was solved by direct methods, and refined by least-squares procedures toR = 0.070 for 552 observed diffraction maxima. The molecules are zwitterions linked by an infinite three-dimensional network of hydrogen bonds via the primary amine nitrogen and carboxylate oxygen atoms. The secondary amine nitrogen atom is not involved in hydrogen bonding.

ChemInform Abstract: CRYSTAL STRUCTURE OF THE DIHYDROPERCHLORATE OF 1,4,8,11‐TETRA‐AZACYCLOTETRADECANE(CYCLAM)

Three-dimensional crystal structure analysis by Patterson and Fourier methods has shown that the title compound consists of centrosymmetrical cations, two of the nitrogen atoms being protonated, and perchlorate ions. There is one formula unit [C10H26N4][ClO4]2 in a triclinic unit cell of dimensions a= 8·081 (3), b= 8·657(3), c= 8·219(2)A, α= 119·23(2), β= 95·05(3), γ= 111·37(2)°, space group P. Refinement by least-squares gave R 0·049 on 1009 diffractometer observations. In the perchlorate ion mean Cl–O is l·405(3)A, uncorrected for libration. The cationic ring contains two centrosymmetrically related protonated nitrogen atoms (N–C 1·504 and 1·490, N–H 0·94 and 0·99 A), and two secondary amine nitrogen atoms (N–C 1·464 and 1·470, N–H 0·91 A). An approximately tetrahedral arrangement about the latter type is completed by a hydrogen atom from the former type which may be forming a weak hydrogen bond. Evidence for N–H ⋯ O hydrogen bonding is equivocal.

Crystal structure of the dihydroperchlorate of 1,4,8,11-tetra-azacyclotetradecane (cyclam)

Three-dimensional crystal structure analysis by Patterson and Fourier methods has shown that the title compound consists of centrosymmetrical cations, two of the nitrogen atoms being protonated, and perchlorate ions. There is one formula unit [C10H26N4][ClO4]2 in a triclinic unit cell of dimensions a= 8·081 (3), b= 8·657(3), c= 8·219(2)A, α= 119·23(2), β= 95·05(3), γ= 111·37(2)°, space group P. Refinement by least-squares gave R 0·049 on 1009 diffractometer observations. In the perchlorate ion mean Cl–O is l·405(3)A, uncorrected for libration. The cationic ring contains two centrosymmetrically related protonated nitrogen atoms (N–C 1·504 and 1·490, N–H 0·94 and 0·99 A), and two secondary amine nitrogen atoms (N–C 1·464 and 1·470, N–H 0·91 A). An approximately tetrahedral arrangement about the latter type is completed by a hydrogen atom from the former type which may be forming a weak hydrogen bond. Evidence for N–H ⋯ O hydrogen bonding is equivocal.