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Cryoreduction of the [FeO2]6 (n = 6 is the number of electrons in 3d orbitals on Fe and pi* orbitals on O2) dioxygen-bound ferroheme through irradiation at 77 K generates an [FeO2]7 reduced oxy-heme. Numerous investigations have examined [FeO2]7 centers that have been characterized as peroxo-ferric centers, denoted [FeO2]per7, in which a ferriheme binds a dianionic peroxo-ligand. The generation of such an intermediate can be understood heuristically if the [FeO2]6 parent is viewed as a superoxo-ferric center and the injected electron localizes on the O-O moiety. We here report EPR/ENDOR experiments which show quite different properties for the [FeO2]7 centers produced by cryoreduction of monomeric oxy-hemoglobin (oxy-GMH3) from Glycera dibranchiata, which is unlike mammalian "globins" in having a leucine in place of the distal histidine; of frozen aprotic solutions of oxy-ferrous octaethyl porphyrin; and of the oxy-ferrous complex of the heme model, cyclidene. These [FeO2]7 centers are characterized as "superoxo-ferrous" centers ([FeO2]sup7), with nearly unit spin density localized on a superoxo moiety which is end-on coordinated to a low-spin ferrous ion. This assignment is based on their g tensors and 17O hyperfine couplings, which are characteristic of the superoxide ion coordinated to a diamagnetic metal ion, and on the absence of detectable ENDOR signals either from the in-plane 14N ligands or from an exchangeable H-bond proton. Such a center would arise if the electron that adds to the [FeO2]6 superoxo-ferric parent localizes on the Fe ion, to make a superoxo-ferrous moiety. Upon annealing to T150 K, the [FeO2]sup7 species converts to peroxo/hydroperoxo-ferric ([FeO2H]7) intermediates. These experiments suggest that the primary reduction product is [FeO2]sup7 and that the internal redox transition to [FeO2]per7/[FeO2H]7 states is driven at least in part by H-bonding/proton donation by the environment.

New copper(II) and zinc(II) complexes of cross-bridged tetraazamacrocyclic ligands derived from 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,7,10-tetraazacyclotridecane ([13]aneN4), and 1,4,7,10-tetraazacyclododecane (cyclen) have been synthesized. The X-ray crystal structures of the two cyclen-derived complexes have been determined and show both metal ions to be in distorted octahedral environments with the ligand in a cis -folded conformation. The bridged-ligand complexes are remarkably stable kinetically under harsh acidic conditions, as seen from their dissociation reactions. The electrochemical and spectroscopic properties of the Cu 2 complexes have also been investigated. # 2003 Elsevier Science B.V. All rights reserved.

The Mn2+ and Fe2+ complexes of the cross-bridged tetraazamacrocyclic ligands, 4,11-dibenzyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1), 4,10-dibenzyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2), 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (3), and 1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (4) provide new compounds of these elements for fundamental studies and applications. These unsubstituted and benzyl substituted derivatives were prepared for comparison of their structures and properties with the known catalytically active dimethyl cross-bridged ligand complexes, which are especially notable for their exceptional kinetic stabilities and redox activity. The X-ray crystal structures of five complexes demonstrate that the ligands enforce a distorted octahedral geometry on the metals with two cis sites occupied by labile ligands. The Fe2+ complexes of the unsubstitued ligands form μ-oxo dimers upon exposure to air, which have also been structurally characterized. Cyclic voltammetry of the monomeric complexes shows reversible redox processes for the M3+/M2+ couples, which are sensitive to solvent, ring size, and ring substitution.

The high spin Co2+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1), 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2), 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3), and racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4) have been synthesized and characterized by X-ray crystallography. The Co(III) complexes of 1-3 were also prepared by the chemical oxidation of the Co(II) complexes. The X-ray crystal structures of Co(1)Cl-2, Co(3)Cl-2, and [Co(3)Cl-2]PF6 demonstrate that the ligands enforce a distorted octahedral geometry on Co(II) and Co(III) with two cis sites occupied by chloro ligands. In contrast, the Co(II) complex of 4 is five-coordinate with trigonal bipyramidal geometry. The methyl groups substituted on the carbon atoms of ligand 4 define a shallow cavity, allowing only one chloride ligand to bind to the chelated metal ion. This difference in coordination geometry causes Co(4)Cl+ to be much more difficult to oxidize (E-1/2 = 1.176 V vs. SHE) than the octahedral Co(II) complexes of 1-3 (E-1/2 from -0.157 to 0.173 V vs. SHE). The Co(III) complexes of 1-3 have three absorbances in their electronic spectra, while typical cis-Co(III)N4X2 complexes have only two. This additional splitting of energy states is attributed to the increased distortion from octahedral resulting from the short ethylene cross-bridge on the macrobicyclic ligands. (C) 2002 Elsevier Science B.V. All rights reserved.

The threading of more or less linear axle molecules through macrocyclic molecules, a fundamental process relating to the formation of interlocked molecular structures, has been investigated through the study in acetone of the equilibrium constants for the formation of pseudorotaxanes by NMR methods. The 30 new axle molecules have in common a secondary ammonium group, present as the thiocyanate salt, and an anthracen-9-ylmethyl group, but are rendered unique by the second amine substituent. All rotaxanes involve the well known polyether macrocycle, benzo[24]crown-8. The constants for the binding of axles having linear groups ranging from 2 to 18 carbon atoms show little variation in binding constant but are divided into two groups by their equilibration rates. Those with less than five methylene groups react rapidly on the NMR timescale, whereas those having more than five methylene groups are slow. Branching inhibits binding, but the effect decreases as the branch is moved away from the amine. Phenyl groups weaken binding when close to the amine but strengthen binding when more remote. Some functional groups decrease pseudorotaxane stability (alcohol functions), whereas others increase binding (carboxylic acid groups).

The crystal structures are reported of trans-dioxocyclam dihydrate, C(10)H(20)N(4)O(2).2H(2)O, a structural isomer of the well known cis-dioxocyclam, and of its novel Ni complex, (1,4,8,11-tetraazacyclotetradecane-2,9-dionato-kappa(4)N)nickel(II) dihydrate, [Ni(C(10)H(18)N(4)O(2))].2H(2)O, the first example of a transition metal complex of this ligand. Both molecules lie on crystallographic centres of inversion. The free ligand has two of its N atoms turned outwards from the ring and hydrogen bonded to water molecules. A major conformational change takes place in the complex in which the ligand binds in a trans tetradentate fashion, as suggested by the electronic spectrum. The nickel(II) ion is low spin, although the electronic spectrum of the complex in water indicates an equilibrium mixture of low-spin and high-spin species. The irreversible electrochemical oxidation of [NiL(1)] (L(1) is deprotonated trans-dioxocyclam, C(10)H(18)N(4)O(2)) in water occurs at a potential of 0.964 V [versus SHE (standard hydrogen electrode)], which is very similar to that for the Ni-cis-dioxocyclam complex.

The novel high spin Ni2+ complexes of the topologically constrained tetraazamacrocycles (1–4) [4,11-dimethyl-1,4,8,11 - tetraazabicyclo[6.6.2]hexadecane (1); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3); racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4)] show striking properties. Potentiometric titrations of the ligands 2 and 4 revealed them to be proton sponges, as reported earlier for 1 [1]. Ligand 3 is less basic, losing its last proton with a pK = 11.3(2). Despite high proton affinities, complexation reactions in the absence of protons successfully yielded Ni2+ complexes in all cases. The X-ray crystal structures of Ni(1)(acac)+, Ni(3)(acac)+ and Ni(1)(OH2)2 2+ demonstrate that the ligands enforce a distorted octahedral geometry on Ni2+ with two cis sites occupied by other ligands. Magnetic measurements and electronic spectroscopy on the corresponding Ni(L)Cl2 (L = 1–3) complexes r...

The high-spin dichloro Mn2+ and Fe2+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1) and 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2) provide durable new compounds of these elements for important fundamental studies and applications. The compounds are especially noteable for their exceptional kinetic stabilities and redox activity. The X-ray crystal structures of all four complexes demonstrate that the ligands enforce a distorted octahedral geometry on the metals with two cis sites occupied by labile chloride ligands. Magnetic measurements reveal that all are high spin with typical magnetic moments. Cyclic voltammetry of the complexes shows reversible redox processes at +0.110 and +0.038 V (versus SHE) for the Fe3+/Fe2+ couples of Fe(1)Cl2 and Fe(2)Cl2, respectively, while the Mn3+/Mn2+ and Mn4+/Mn3+ couples were observed at +0.585 and +1.343 V, and +0.466 and +1.232 V for the complexes Mn(1)Cl2 and Mn(2)Cl2, respectively. Mn2+(1) was found to react with H2O2 and o...

The novel bicyclic pentadentate ligand 5-methyl-1,5,9,24,25-pentaazapentacyclo[7.7.7.5.5]pentacosane11,13,15,18(25),20,22-hexene (L1) has been synthesized. Because of its cross-bridged topology it exhibits a relatively rigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structure of the monoprotonated ligand salt, HL1ClH2O [orthorhombic, P212121, a = 9.4405(5) A, b = 13.3617(5) A, c = 16.710(1) A]. The complexes of L1 with both iron(II) and manganese(II) have been characterized, including the crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P21/n, a = 10.0460(5) A, b = 19.237(9) A, c = 15.6254(8) A, beta = 95.97(2)degrees and a = 7.745(2) A, b = 22.786(4) A, c = 14.639(4) A, beta = 105.074(10)degrees respectively]. The manganese complex is high spin with mueff = 5.96 and theta = 2.5 +/- 0.8 cm(-1), indicating weak ferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxide have been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidenced by their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl-phenyl-nitrone.

The parallel syntheses of two new cross-bridged tetraazamacrocyclic complexes whose ligands are derived from 1,4,8,11-tetraazacyclotetradecane (cyclam = 14N4) and rac-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane (tetB = 14N4Me(6)) have been characterized through the crystal structure determination of every stepwise intermediate ligand in the multistep ligand syntheses. These structures show that although the final ligand skeletons are nearly identical, the immediate precursors differ greatly because of the six additional methyl groups of the 14N4Me(6) macrocycle. The inversion from one diastereomer to another of the tetracycle derived from rac-14N4Me(6) has been chemically induced through the successive addition of methyl groups to the reactive tertiary nitrogens, and the novel heterocycles produced have been crystallographically characterized with one showing a conformation not previously known for these systems. The structures of the two copper(II) complexes have significant geometrical differences, and accordingly, their electrochemical and spectroscopic properties are compared. The complexes exhibit remarkable kinetic stability under harsh conditions.

The design and synthesis of a new family of tridentate Schiff base ligands for use in octahedral molecular templates has been successfully demonstrated. As anticipated, two molecules of the ligand, 2,6-pyridinedicarboxaldhydebis(p-hydroxyphenylimine), coordinate equatorially to six-coordinate octahedral metal ions to give orthogonally oriented molecular turns around the anchoring metal ion. This new template offers the advantages that (1) syntheses of the ligand and its complexes are straightforward, giving high yields in simple, one-pot reactions, and (2) structural variations are easily accomplished. X-ray structural analysis has shown that the ligand will only function as a turn when its spatial organization is controlled by coordination to a metal ion. Upon chelation, the phenolic groups are directed across and beyond the metal ion center, and, unlike earlier ligands of this general type which lacked reactive moieties, substitution reactions may be carried out at the free phenolic groups of the octahedral complex. These reactions remain to be optimized in order to achieve the long-term goal of proving their value as synthons for interlocked molecules.

The kinetics of O 2 binding to a vacant coordination site on the cobalt(II) ion have been determined, revealing a radical-like character for the reaction. Reversible oxygenation of Co(II) cyclidenes (C4, C5, C6, C8, C12-bridged and unbridged) was studied by a cryogenic stopped-flow method. In the presence of axial base, kinetic parameters are insensitive to the nature of the solvent, and negative entropies of activation suggest that dissociation of a solvent molecule is not the rate-determining step for the dioxygen binding process. This is in contrast to the behavior of previously studied Co(II) complexes. A very low activation energy (1–4 kcal mol −1 ), typical of diffusion controlled processes, was found for dioxygen binding. The binding rate constants for the highest affinity complexes (10 8 M −1 s −1 ) are comparable to the values for natural dioxygen carriers. The size of the lacuna primarily affects the dioxygen binding rates, while the axial bases influence the dioxygen dissociation rates.

The binding of CO to a lacunar Fe(II) cyclidene complex is characterized by very negative values for the activation entropy and activation volume, whereas the reverse dissociation reaction is accompanied by small positive activation entropy and activation volume data. The constructed volume profile suggests that, in the transition state, CO disappears completely into the ligand pocket during partial Fe−CO bond formation, followed by a high-spin to low-spin transition on Fe(II) during which the metal center moves into the ligand plane and accounts for the subsequent volume decrease.

A new type of isomerism has been detected in the cyclidene family of lacunar dioxygen carriers, providing an additional structural variable for the control of their oxygen affinity. In those rare complexes that do not have methyl substituents on the primary macrocycle, NMR and X-ray crystallographic data indicate that, in addition to their usual cis orientation, the bridges can also adopt a trans orientation. In the crystal structure of [Co(C(8)MeHH[16]cyclidene)](PF(6))(2).3CH(3)OH, the bridge has this trans orientation with one end in the "lid-on" configuration while the other end is "lid-off". The trans orientation of the bridge is identified as the principal cause of the decreased dioxygen affinity of such unsubstituted cyclidenes.

The kinetics of carbon monoxide binding and dissociation have been studied for a series of lacunar iron(II) cyclidene complexes to elucidate the dependence of dynamic parameters on the various structural features of these versatile compounds. Ligand substituents have large effects on the binding and dissociative rate constants, and remarkably, four distinctly different steric effects have been observed. (1) Changing cavity size alters the rate of CO binding by as much as 4 orders of magnitude, presumably by constraining access to the metal ion. (2) Decreases in cavity size also can increase the rate of CO dissociation by a factor of 10 or so. (3) Placing bulky groups in the path CO must follow to enter the cavity decreases the rate of binding because of steric effect (1), but these same obstructions may also decrease the rate of dissociation by blocking the escape path and, possibly, fostering geminate recombination. (4) Proximal ligand strain both decreases the rate of binding and increases the rate of C...

A dicopper(II) complex with an unsymmetrical dicompartmental ligand containing bridging phenolic oxygen atoms was synthesized by stepwise condensation, in the presence of copper(II) ions, of 2,6-diformyl-4-methylphenol and diaminopropane, followed by hydroxylamine. The complex was isolated and characterized as Cl-, [Cu2Cl4]2-, and ClO4- derivatives. A byproduct of the reaction, a copper(II) complex with a substituted salycilaldoxime, was also structurally characterized. The structure of the binuclear cation of major interest is nearly planar, with the copper(II) ions slightly displaced to opposite sides of the plane of the donor atoms (

The preparations and structures of three vaulted cyclidene complexes are compared with the two previously reported. All show similar structures with large rigid cavities partly closed off by the piperidine risers, illustrating in particular the attractive effect of van der Waals forces resulting in the incorporation of solvent molecules or [PF 6 ] − ions nesting on the edges of the cavities. However, the detailed geometries vary, according to the nature of the ligand substituents, the metal, the counter-ion and the lattice solvent molecules. These give rise to differing orientations of the capping aromatic rings and the piperidine risers.

Unbridged Ni(II) cyclidene complexes have been prepared with bulky substituents at the terminal nitrogen atoms (R2 = -C(Me)2CH2N(Me)2; -CH(Ph)2; -CH2C(Me)3; -CH2CH(Ph)2) (substituent R3 at the adjoining carbon = Me). Complexes containing the last two substituents and bridged with m-xylylene and (CH2)6 have also been synthesised. The effects of the bulky substituents on 13C n.m.r spectra, electrochemical behaviour and oxygen binding ability are examined. The crystal structures of the m-xylylene-bridged complexes with R2 = CH2C(Me)3, R3 = Me (I) and R2 = Me, R3 = Ph (II) have been determined; both are monoclinic, P21\c, with (I) a = 13.463(1); b = 14.506(2); c = 26.72492)A, β = 91.45(1), R = 0.082 for 3895 observed (I/σ(I)> = 2.0) reflections; (II) a = 24.721(6), b = 10.934(3), c = 16.321(5)A, β = 97.30(2)°, R = 0.074 for 2992 observed (I/σ(I)> = 3.0) reflections

The factors controlling the reversible dioxygen binding in lacunar cobalt(II) cyclidene complexes (Figure 1) have been examined. Extensive structural variations reveal that the dioxygen affinity can be controlled by both steric and electronic means. The dioxygen affinity decreases monotonically with the length of a polymethylene bridging group (R 1 , Figure 1) from octamethylene to tetramethylene; no binding occurs with the still shorter trimethylene bridge. From the analysis of a large array of experimental data, the effects ofthe R 2 and R 3 substituents on dioxygen affinity are found to be mainly electronic; for example, electron-withdrawing groups at the R 2 and R 3 positions decrease the affinity

The synthesis of four novel cobalt(II) cyclidene complexes with long polymethylene bridges is described. These complexes have been found to reversibly bind dioxygen in a manner similar to that of their shorter bridged analogs. Dioxygen affinities are reduced for bridge lengths exceeding that of octamethylene, an effects on small-molecule binding that are associated with the long bridge have been examined by comparison of the X-ray crystal structure of th undecamethylene-bridged cobalt(III) complex with the shorter bridged analogues.

Infrared spectra were obtained for dioxygen adducts of a series of cobalt(II) and iron(II) cyclidene complexes with 1-methylimidazole as the axial base. The v o-o bands were located in the range 1137–1163 cm−1, and their identity was confirmed by 18O2 isotopic substitution. The frequency was found to be insensitive of the metal ion but dependent on both the σ and π electron donating properties of the cyclidene ligands. There is no apparent correlation between v o-o and the oxygen affinity; v o-o alternates with the even or odd number of carbon atoms in the bridging polymethylene group because of a symmetry effect on the π electron system of the ligand.

The nickel(II) and cobalt(II) complexes have been synthesized and charactetized as the first examples of metal complexes of a 14-membered cyclidene. [(2,3,16,17,19,29-Hexamethyl-3,1(,20,23,26,29-hexaazabicyclo[16.6.6]tiaconta-1,17,19,23,25,29-hexaene-k 4 N 20,23,26,29 )nickel(II)] hexafluoxophosphate, NiC 30 H 52 N 6 P 2 F 12 tallized in the orthorhombic space group Pna2 1 .

The pentadentate ligand DPC (DPC=4,7-bis(2-picolyl)-4,7-diaza-1-oxacyclononane) reacts with FeC 2 in MeOH to teh produce the high (S=2) iron(II) complex (λ max =260 and 378 nm in water). The structure of the complex was determined by X-ray crystallography. Crystal data: orthorhombic space group P2 1 2 1 2 1 .

The electronic structures of the bis(hydroxo)manganese(IV) and oxohydroxomanganese(IV) complexes [Mn(IV)(OH)(2)(Me(2)EBC)](2+) and [Mn(IV)(O)(OH)(Me(2)EBC)](+) were probed using electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD spectroscopies. The d-d transitions of [Mn(IV)(OH)(2)(Me(2)EBC)](2+) were assigned using a group theory analysis coupled with the results of time-dependent density functional theory computations. These assignments permit the development of an experimentally validated description for the pi and sigma interactions in this complex. A similar analysis performed for [Mn(IV)(O)(OH)(Me(2)EBC)](+) reveals that there is a significant increase in the ligand character in the Mn pi* orbitals for the Mn(IV)=O complex relative to the bis(hydroxo)manganese(IV) complex, whereas the compositions of the Mn sigma* orbitals are less affected. Because of the steric features of the Me(2)EBC ligand, we propose that H-atom transfer by these reagents proceeds via the sigma* orbitals, which, because of their similar compositions among these two compounds, leads to modest rate enhancements for the Mn(IV)=O versus Mn(IV)OH species.

The preparation and crystal structure of 1,10,13,18-tetraazatricyclo[8.6.6.0 3,8 ]docosa-3,5,7-triene-11,17-dione monohydrate, C 18 H 26 N 4 O 2 .H 2 O, are described. The molecule has a U-shaped conformation, with the N atoms well oriented for metal complexation.

3,4-Bis(alkylamino)-3-cyclobuten-1,2-dithiones (cis-dithiosquaramides, LH 2 ) react with divalent metal acetates to give neutral 2:1 complexes of the general formula M II (LH) 2 -xH 2 O (M II =Ni, Cu, Pd). The ligands bind in a didentate S 2 Cashion Corming a square planar M II S 4 coordination sphere.

The preparation and crystal structures of (4,11-di­benzyl-1,4,8,11-tetra­aza­bi­cyclo­[6.6.2]­hexa­decane-κ4N)copper(I) hexa-fluorophosphate, [Cu(C26H38N4)]PF6, and acetonitrile(4,11-dibenzyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-κ4N)-copper(II) bis(hexafluorophosphate), [Cu(C2H3N)(C26H38-N4)](PF6)2, are described. The CuI ion is tetracoordinated in a very distorted tetrahedron, while the CuII analogue is pentacoordinated in a square pyramid.

The synthesis, characterization and structure are described for new cobalt complexes, with a BF2 + bridged, bis(a-dioxime) ligand, based upon a sterically demanding framework derived from an anthracene Diels-Alder adduct. The ligand provides a deep cleft within which axial ligands and/or O2 can bind. The crystal structures of the bis- and mono(BF2 +) bridged complexes have space groups P21/c and P I, respectively, with unit cell dimensions a = 12.662(2) A, b = 16.430(3) A, c = 10.438(3) A, β = 103.51(2)°, a = 12.046(1)A, b = I7.596(3)A, c = 9.939(I)A, a = 105.15(1)°, β = 102.87(1)°, and γ = 78.13(1), respectively. For both complexes Z = 2 and the residuals R and R w were 0.070, 0.104, and 0.059, 0.075, respectively. ESR studies show that the cobalt(II) complexes have a strong tendency to bind two axial nitrogen bases, adopting a coordination number of six. The dioxygen affinity of the new cobalt(II) dioxygen carrier is limited by the competition between axial base binding and O2 binding. This ext...

N-Monosubstituted dithiooxamides react with diamines to give tetradentate dithiooxamide ligands (LH 4 ) of the general formula RNHC(S)C(S)NH(CH 2 ) n NHC(S)C(S)NHR (R=c-C 5 H 9 and c-C 6 H 11 , n=2; R=n-C 12 H 25 and C 6 H 5 CH 2 , n=2-4). Reaction of these ligands with Ni(II) gives cationic complexes of the general formula [Ni(LH 4 )] 2+ under acidic conditions, neutral complexes of formula Ni(LH 2 ) under neutral conditions, and a polymeric material of approximate formula (Ni 2 L) n under basic conditions

The preparation and crystal structure of chloro(4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-κ 4 N)-palladium(II) chloride dihydrate, [PdCl(C 14 H 30 N 4 )]Cl.2H 2 O, are described. The Pd II ion is coordinated to all four N atoms of the folded macrobicycle and to a single chloride ligand in a square-pyramidal geometry. The bond to the axial N atom is considerably longer than the others [Pd-N ax 2.461(3) and average Pd-N eq 2.097 (10) A]. The Pd-Cl distance is 2.3407 (10) A.

A new model for the T-form of hemoglobin has been developed; it consists of a cobalt(II) complex with a pentadentate ligand in which the binding of the axial ligand is inhibited by a steric device. The compounds reported here are isomeric lacunar cyclidene complexes containing a pyridyl group covalently attached to the macrocycle. One isomer possesses a stereochemistry suitable for the intramolecular coordination of the pyridine nitrogen, as demonstrated by ESR experiments on the cobalt(II) complex. A crystal structure is reported for one of the isomers: (hexamethyl-23-[2-(1-methylpyridiniumyl)] hexaazabicyclo[10.7.7]hexacosahexaene-k 4 N) nickel(II) iodide, C 32 H 5 I 3 NiH 2 O, orthorhombic, Pna2 1

The preparation and crystal structure of the title complex, [CuCl 2 (C 7 H 19 N 3 )], are described. The Cu II ion has distorted tetragonal pyramidal geometry, with Cl axial; the axial Cu-Cl distance [2.505 (1) A] is elongated compared with the basal Cu-Cl distance [2.400 (1) A]. In the basal plane, Cu-N(tertiary) [2.138 (3) A] is considerably longer than Cu-N(primary) [1.985 (4) A mean], presumably reflecting the reduced basicity of the ligand atom.

In the structure of aquachloro[7,10,13-trioxa­3,17,23-triazabicyclo[17.3.1]tricosa-1 (23),2,17,19,21-pentaene-N,N',N′′]copper(II) hexafluorophosphate acetonitrile solvate, the CuII ion is pentacoordinate with square-pyramidal coordination geometry, with a relatively long axial bond to water [2.244 (5) A] and with the shortest Cu-N bond being to the pyridine N atom. The water molecule is also hydrogen bonded to two O atoms of the ligand. The complex is folded about the N-Cu-N axis, the polyether chain being nearly planar and making an angle of about 135° with the pyridine ring.

Molecular dynamics simulations have been used to study the three-dimensional distribution of methanol solvent molecules around three cobalt(II) cyclidene complexes differing in details of their ligand structures. The ligands are a planar unbridged 14-membered macrocycle in Co([14]Cyc), a saddle-shaped unbridged 16-membered macrocycle in Co([16]Cyc), and a lacunar bridged 16-membered macrocycle in Co(C6[16]Cyc). All three complexes contain five-coordinate cobalt(II) with the metal ion bound to four nitrogen donor atoms from the macrocycle and one nitrogen donor from an axial methylimidazole. Distinctly different solvation patterns are exemplified for the three complexes by the positions of the maximum in the Co-O pair distribution function (at r(Co-O) = 2.5, 3.7, and 4.5 Å for Co([14]Cyc), Co([16]Cyc), and Co(C6[16]Cyc), respectively) and by the number of methanol molecules within the macrocyclic cleft (1.5, 0.7, and 0.4 molecules at a Co-O distance of 5.25 Å in the "cavity", respectively). Analysis of the anisotropic solvent structure reveals the presence of a methanol molecule directly above the cobalt(II) center, at a distance of ca. 2.5 Å, for planar Co([14]Cyc), and the absence of solvent from such close proximity to the metal ion for the remaining complexes. The bridge further protects the sides of the cavity from the solvent. The width of an empty cavity of Co(C6[16]Cyc) shrinks by 0.3 Å in methanol solution, as compared to vacuum simulations. These results confirm the experimentally based (decrease in absolute value of enthalpies and entropies of dioxygen binding) suggestion that extensive solvation of the cobalt(II) center reduces its accessibility to incoming small molecules.

A family of Mn3+ and Fe3+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1) and 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2) has been prepared by the chemical oxidation of the divalent manganese and iron analogues. The ligands are ethylene cross-bridged tetraazamacrocycles derived from cylam and cyclen, respectively. The synthesis and characterization of these complexes, including X-ray crystal structure determinations, are described. The structural evidence demonstrates that the tetradentate ligands enforce distorted octahedral geometries on the metal ions, with two cis sites occupied by labile ligands. Magnetic measurements reveal that the complexes are high spin with typical magnetic moments. Cyclic voltammetry shows reversible redox processes for the Fe3+/Fe2+ couples of the iron(III) complexes, while Mn3+/Mn2+ and Mn4+/Mn3+ couples were observed for the complexes with manganese(III). The manganese chemistry of 1 was studied in depth. The dichloro manganese(III) cation of 1 undergoes facile ligand substitution reactions at the labile, monodentate sites, for example substituting azide for chloride ligands. Air oxidation of the dichloro complex of Mn (1)2+ in basic solution does not give the expected mu-oxo dimeric product common to manganese. Instead, an unusual manganese(III)-OH complex has been isolated from this reaction and structurally characterized. A similar reaction under slightly different conditions gives a putative MnIII(OH)2 complex that metathesizes to MnIII(OMe)2 upon recrystallization from methanol.

The preparation and crystal structure of 1,10,13,18-tetraazatricyclo[8.6.6.0 3,8 ]docosa-3,5,7-triene-11,17-dione monohydrate, C 18 H 26 N 4 O 2 .H 2 O, are described. The molecule has a U-shaped conformation, with the N atoms well oriented for metal complexation.

The preparation and crystal structure of bis(10b,10c-cis-3a,5a,8a,10a-tetraazaperhydropyrene)copper(I) hexafluorophosphate, [Cu(C 12 H 22 N 4 ) 2 ]PF 6 , are described. The Cu I ion lies on an inversion centre and is linearly coordinated, with one bond to each of two tetracyclic tetraamine ligands [Cu-N = 1.976 (2) A].

The kinetics of O2 binding to a demonstrably vacant coordination site on a cobalt(II) ion are determined, revealing a radical-like character for the reaction, with a very low activation barrier (ca. 1–2 kcal mol–1) and large entropically controlled rate constants, whose values approach those for myoglobin and haemoglobin (up to 108 dm3 mol–1 s–1).

Crystal structure determinations for two salts show that the structures of metal-free cyclidene ligand salts are critically dependent on the degree of protonation, showing either a structure close to those found for corresponding metal complexes, or an entirely different conformation stabilised by N–H ⋯ Cl hydrogen bonds in an ‘ion quartet’, a cluster formed by the [LH5]5+ ion interacting with 3 Cl– ions.

The synthesis and characterization of a new cobalt(II) complex [Co(Me2H2Me2malox)(py)2][Me2H2Me2malox = 4,4′-oxalyldinitrilodi(pent-2-en-2-olato)(2–), py = pyridine], based on a chelating ligand containing no saturated chelate rings, is described together with the corresponding cobalt(III) complex. The cobalt(II) complex binds dioxygen in a reversible manner in pyridine solution at temperatures near –20 °C. The corresponding copper(II) complex [Cu(Me2H2Me2Me2malox)] crystallizes in the monoclinic system P21/c with a= 8.866(1), b= 16.029(1), c= 9.106(1)A, β= 97.57(2)° and Z= 4. Structural refinement resulted in R= 0.0423 and R′= 0.0436 for 2153 observed reflections. Studies of [Cu(Me2H2Me2malox)] using X-ray crystallography and IR spectroscopy guided the development of the synthetic procedure used in the isolation of the cobalt(II) adduct. A six-co-ordinate cobalt(III) complex is reported as a model for the cobalt–dioxygen adduct. Proton exchange with solvent has been observed using NMR spectroscopy and implications for the rational design of dioxygen carriers is discussed.

A new macrocyclic ligand having a carefully selected pendant group has been synthesized and its cobalt(III) complex has been prepared and characterized by X-ray crystallography. 1,4,7,10-Tetra-azacyclododecane-N-m-toluic acid was prepared via the corresponding nitrile, from m-cyanobenzyl-bromide and the tetra-azamacrocycle, followed by formation of the cobalt(III) complex and then hydrolysis of the cyano group in the complex. The structure reveals a novel dinuclear structure in which the dangling carboxyl groups like the two metal ions. This is consistent with the molecular design since the pendant group was selected to prevent chelation of the carboxyl group to the same metal ion as the parent macrocycle. Crystal data: [{Co(C16H25N4O2)H2O}2][ClO4]4·6H2O: orthorhombic, space group Pbcn, a= 25.346(7), b= 15.722(2), c= 25.720(4)A, Z = 8 (dimers), and R= 0.064 for 2 806 unique observed [I/σ(I) 3.0] reflections. The crystal contains two independent but essentially identical dimers with two-fold symmetry, containing octahedral cobalt(III), cis-co-ordinated to four nitrogen atoms of the macrocycle, to a carboxylate oxygen, and to a water molecule.

A series of square-planar iron (II) complexes has been prepared with synthetic dianionic unsaturated tetraaza macrocyclic ligands that are devoid of functional substituents and vary in ring size from 14 to 16 members. The temperature dependence of the magnetic susceptibility confirms the unusual intermediate spin (S = 1) ground state for these square-planar derivatives. In addition, dicationic iron (II) complexes of these ligands have been prepared by protonation of the neutral square-planar complexes. Two types of protonation products have been obtained, including the complexes of tetradentate bis-..beta..-diimine macrocyclic ligands and two novel derivatives in which acetonitrile molecules have added to the apical ..gamma..-carbon of the charged six-membered chelate rings. Ring size effects appear most dramatically in the reactions of the planar complexes with acetonitrile, in which case ring size determines the nature of the product. However, it is also evident both in electronic and Moessbauer spectral data that ring size exerts a great influence on ligand field strengths. The six-coordinate complexes Fe(macrocycle)-(pyridine)/sub 2//sup 2 +/ containing 14- and 15-membered ring macrocyclic ligands have low-spin ground states, while a 16-membered ring derivative exhibits a spin-state equilibrium.