Tuning Magnetic Properties of a Carbon Nanotube-Lanthanide Hybrid Molecular Complex through Controlled Functionalization.

Molecular magnets attached to carbon nanotubes (CNT) are being studied as potential candidates for developing spintronic and quantum technologies. However, the functionalization routes used to develop these hybrid systems can drastically affect their respective physiochemical properties. Due to the complexity of this systems, little work has been directed at establishing the correlation between the degree of functionalization and the magnetic character. Here, we demonstrate the chemical functionalization degree associated with molecular magnet loading can be utilized for controlled tuning the magnetic properties of a CNT-lanthanide hybrid complex. CNT functionalization degree was evaluated by interpreting minor Raman phonon modes in relation to the controlled reaction conditions. These findings were exploited in attaching a rare-earth-based molecular magnet (Gd-DTPA) to the CNTs. Inductively coupled plasma mass spectrometry, time-of-flight secondary ion mass spectrometry and super conducting quantum interference device (SQUID) measurements were used to elucidate the variation of magnetic character across the samples. This controlled Gd-DTPA loading on the CNT surface has led to a significant change in the nanotube intrinsic diamagnetism, showing antiferromagnetic coupling with increase in the Weiss temperature with respect to increased loading. This indicates that synthesis of a highly correlated spin system for developing novel spintronic technologies can be realized through a carbon-based hybrid material.

Outer-sphere anion recognition by a cyclen-based octadentate europium(III) complex: pH dependent recognition of ortho-phthalic acid.

An octadentate cyclen-based europium complex with amidic and hydroxyalkyl pendent moieties exhibits pH dependent ligand denticity associated with anion recognition. Unusually high hydration numbers are determined for ortho-phthalate ternary outer-sphere complexes for which modulation of lanthanide-based luminescence is observed.

The preparation of N-acetyl-Co(III)-microperoxidase-8 (NAcCoMP8) and its ligand substitution reactions: a comparison with aquacobalamin (vitamin B(12a)).

The synthesis of the Co(III) porphyrin octapeptide N-acetyl-Co(III) microperoxidase-8 (NAcCoMP8) is described. NAcCoMP8 provides a means of comparing and contrasting the chemistry of Co(III) porphyrins and corrins to assess the influence of the macrocycle. Log K values, and ΔH and ΔS, for the coordination of anionic (CN(-), N3(-), NO2(-), HSO3(-)) and neutral (pyridine, N-methylimidazole, methoxylamine and hydroxylamine) ligands by aquacobalamin (H2OCbl(+)) and NAcCoMP8 are reported. Anions bind more strongly to H2OCbl(+) than to NAcCoMP8 while the converse is true for the neutral ligands. Density Functional Theory (DFT) calculations and QTAIM analyses suggest the bonding between Co(III) and these ligands is predominantly ionic although anionic ligands induce a significant covalency, the extent of which is important for the stability of the complex. The CoL bond length (L=an anion) in a Co(III) corrin, while longer than in a Co(III) porphyrin, is shorter than might be expected as assessed from CoL bond lengths when L=neutral ligand. It is likely that this stems from coulombic interaction between L and the residual charge at the metal center (2+ in corrin; 1+ in porphyrin). Co(III) in H2OCbl(+) is more labile towards substitution by CN(-) than NAcCoMP8 but the converse is true when the entering ligand is neutral N-methylimidazole. The extent of participation of the incoming ligand in the transition state of the reaction is controlled by the log K value so the nature of the incoming ligand determines in which of these two macrocyclic systems Co(III) is the more labile.

Bis-(2-hy-droxy-eth-yl)ammonium 2-bromo-phenolate.

In the crystal structure of the 1:1 title salt, C(4)H(12)NO(2) (+)·C(6)H(4)BrO(-), hydrogen-bonding inter-actions originate from the ammonium cation, which adopts a syn conformation. A gauche relationship between the C-O and C-N bonds of the 2-hy-droxy-ethyl fragments also facilitates O-H⋯O inter-actions of bis-(2-hy-droxy-eth-yl)ammonium cation chains to phenolate O atoms. The resulting double-ion chains along [100] are further linked by N-H⋯O inter-actions, forming chains parallel to [110].

Bis-(2-bromo-eth-yl)ammonium bromide.

The title salt, C(4)H(10)Br(2)N(+)·Br(-), crystallizes with four cations and four anions in the asymmetric unit. In the crystal, the bis-(2-bromo-eth-yl)ammonium cations and bromide anions are linked into chains by N-H⋯Br hydrogen bonds describing a binary C(2) (1)(4) motif along [010]. Each of these chains is formed by a unique cation and anion pair. The ammonium cations occur in the less preferred anti conformation, characterized by different NCCBr torsion angles. Adjacent chains are linked by weak C-H⋯Br inter-actions, forming a three-dimensional network. The crystal studied was a pseudo-merohedral twin with twin ratio 0.640 (2):0.360 (2).

Hydrogen-bond inter-actions in morpholinium bromide.

In the title compound, C(4)H(10)NO(+)·Br(-), which was synthesized by dehydration of diethano-lamine with HBr, morpholinium and bromide ions are linked into chains by N-H⋯Br hydrogen bonds describing a C(2) (1)(4) graph-set motif. Weaker bifurcated N-H⋯Br inter-actions join centrosymmetrically related chains through alternating binary graph-set R(4) (2)(8) and R(2) (2)(4) motifs, to form ladders along [100]. In addition, C-H⋯O inter-actions between centrosymmetric morpholinium cations link ladders, via[Formula: see text](8) motifs, to yield sheets parallel to (101), which in turn are crosslinked by weak C-H⋯O inter-actions, related across a glide plane, to form a three-dimensional network.

N,N'-bis(2-hydroxycyclohexyl)-N,N'-bis(2-hydroxyethyl)ethane-1,2-diaminium dichloride.

The achiral meso form of the title compound, C(18)H(38)N(2)O(4)(2+)·2Cl(-), crystallizes to form undulating layers consisting of chains linked via weak hydroxyalkyl C-H...Cl contacts. The chains are characterized by centrosymmetric hydrogen-bonded dimers generated via N-H...Cl and hydroxycycloalkyl O-H...Cl interactions. trans-N-Alkyl bridges subdivide the chains into hydrophilic segments flanked by hydrophobic cycloalkyl stacks along [001].

Amino-alcohol ligands: synthesis and structure of N,N'-bis(2-hydroxycyclopentyl)ethane-1,2-diamine and its salts, and an assessment of its fitness and that of related ligands for complexing metal ions.

The synthesis and solid state structure of the amino-alcohol ligand, (1R,2R,1'S,2'S)-N,N'-bis(2-hydroxycyclopentyl)ethane-1,2-diamine (Cyp(2)en) obtained by the reaction of cyclopentene oxide with ethylenediamine, as well as its bromide, chloride, perchlorate, and nitrate salts, is reported. In all five structures, the Cyp(2)en ligand sits on a center of inversion with the two amino groups and two hydroxyl groups of the cyclopentyl moieties trans to each other across that inversion center. Comparing this conformation to that of a density functional theory (DFT)-calculated structure of cis-[Ni(Cyp(2)en)(H(2)O)(2)](2+) suggests that the ligand is not well pre-organized for coordinating a metal ion. The likely solution structure of this ligand, and that of the related ligands bis(2-hydroxy)ethane-1,2-diamine (Bheen) and bis(2-hydroxycyclohexyl)ethane-1,2-diamine (Cy(2)en), was explored using molecular mechanics modeling with the generalized AMBER force field. A Boltzmann distribution of the lowest energy conformations found shows that 36 conformations of Bheen each contribute more than 1% to the population at 300 K; this decreases to 27 conformations for Cyp(2)en and to 12 for Cy(2)en, and Cy(2)en is the most rigid of the three ligands. The population-weighted root-mean-square deviation (rmsd) between these lowest energy conformations and the conformation required for coordinating a metal ion increased in the order Cy(2)en < Cyp(2)en < Bheen, while stability constants for coordinating Ni(II) decrease in the order Cy(2)en > Bheen > Cyp(2)en. The high pre-organization of Cy(2)en is due to an intramolecular N-H....O hydrogen bond, apparently missing in the other two ligands. Pre-organization is likely to be an important, but not the only factor, that controls the value of the stability constants of these ligands with metal ions.

Hydrogen-bonding controls the solid-state and enantiomeric conformations of the amino alcohol ligand 2-[(2-hydroxyethyl)amino]cyclohexanol.

The crystal structure of the title compound, C(8)H(17)NO(2), consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen-bonded dimers, generated via N-H...O and O-H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction.

The structure of N,N'-bis(2-hydroxyethyl)ethane-1,2-diamine and its complexes with Zn(II) and Cd(II).

The crystal structure of the nitrate salt of N,N'-bis(2-hydroxyethyl)-ethane-1,2-diamine (BHEEN), and its complex with Zn(II) and Cd(II) are reported. (H(2)BHEEN)(NO(3))(2) packs in a layered structure with a herringbone pattern within each layer arising from H-bonding between amino and alcohol protons and NO(3)(-) counterions. In [Zn(BHEEN)(2)]Cl(2), each ligand coordinates to Zn(II) through its two N-donors producing a distorted tetrahedral geometry at the metal centre. The two hydroxyethyl arms of each ligand are trans to each other and the crystals obtained contained a racemic mixture of the bis-trans-R,R and the bis-trans-S,S isomers. All four hydroxyl groups are H-bonded to chloride counter ions, creating a layered structure. Whilst distant from the metal ion (average 3.00 A), the four O atoms of the pendent hydroxylamino groups appear positioned to interact with the metal. The orientation of the arms is preserved in a B3LYP gas phase calculation of the structure. An analysis using Bader's Atoms in Molecules indicates that the Zn-N bonds are predominantly ionic with some covalent character and that there is a weak interaction between the metal and the hydroxyl groups. Several other weak interactions including four O...HN, five O...HC and a H-H dihydrogen bond were identified. The Cd(II) complex of BHEEN crystallised as a dimer [(mu-Cl)(2)(Cd(BHEEN)Cl)(2))] with two asymmetrically-bound bridging Cl(-) ligands and a terminally-coordinated Cl(-) on each metal ion. One hydroxyl group of each ligand is coordinated to the metal and the uncoordinated hydroxyl group is H-bonded to the H atom of the coordinated hydroxyl group of the second ligand in the complex. The ESI-MS spectrum shows the presence of di-cadmium complexes, but the most intense peaks are due to mono-cadmium complexes. The gas phase B3LYP structure of the dimer energy-minimises into two monomers and the longer bond between Cd(II) and bridging Cl(-) breaks. Hence, dimerisation may be a consequence of the crystallisation process and the dimer may not be the predominant species in solution.

Complexation of mercury(I) and mercury(II) by 18-crown-6: hydrothermal synthesis of the mercuric nitrite complex.

A dimercury(I) 18-crown-6 complex is isolated, and its possible role in the hydrothermal preparation of the mercuric nitrite complex is discussed. The reported structures are of [Hg(2)(18-crown-6)(2)(H(2)O)(2)](ClO(4))(2) (1), monoclinic, C2/c, a = 21.0345(9), b = 12.1565(5), c = 16.8010(7) A, beta = 113.2000(10) degrees , V = 3948.7(3) A(3), Z = 16, R = 0.0230; [Hg(18-crown-6)](NO(2))(2) (2), monoclinic, P2(1)/c, a = 8.027(5), b = 14.437(9), c = 7.827(5) A, beta = 95.165(11) degrees , V = 905.6(10) A(3), Z = 2, R = 0.0175. The complex cation in compound 1 consists of a mercurous dimer exhibiting a Hg-Hg bond length of 2.524(2) A. Non-bonding interactions between adjacent crown ether macrocycles across the Hg-Hg bond result in large variations in mercury to oxygen distances within equatorial coordination sites. At low pH compound 1 is proposed to be preferentially formed under hydrothermal conditions affording compound 2 upon disproportionation. Nitrite ions ligate via a unidentate nitrito (cis to metal) coordination mode as interpreted using vibrational (infrared) spectroscopy. The conformation adopted by 18-crown-6 in compounds 1 and 2 is closely related to a D(3d) conformation as evidenced by X-ray crystallography. Band splitting readily observed in vibrational spectra of the metal free crown ether, attributed to vibrational modes of oxyethylene fragments, is absent in spectra of 1 and 2 confirming a regular D(3d) macrocyclic orientation. Short Hg-O bonds observed for axially coordinated water molecules in 1 and coordinated nitrite ligands in 2, illustrate the prevalence of relativistic effects commonly observed in mercury complexes.

Complexation of metal ions of higher charge by the highly preorganized tetradentate ligand 2,9-bis(hydroxymethyl)-1,10-phenanthroline. A crystallographic and thermodynamic study.

The metal ion selectivity for M(III) (M = metal) ions exhibited by the highly preorganized ligand PDALC is investigated (PDALC = 2,9-bis(hydroxymethyl)-1,10-phenanthroline). The structures are reported of [Bi(PDALC)(H(2)O)(2)(ClO(4))(3)] x H(2)O (1), monoclinic, P2(1)/c, a = 12.8140(17), b = 19.242(3), c = 9.2917(12) A, beta = 91.763(2) degrees, V = 2289.9(5) A(3), Z = 4, R = 0.0428; [Th(PDALC)(NO(3))(4)] x 3 H(2)O (2), monoclinic, P2(1)/n, a = 7.876(3), b = 22.827(9), c = 12.324(5) A, beta = 94.651(6) degrees, V = 2208.4(15) A(3), Z = 4, R = 0.0669; [Cd(PDALC)(2)](ClO(4))(2) (3)), triclinic, P1, a = 7.5871(16), b = 13.884(3), c = 14.618(3) A, alpha = 74.081(2) degrees, beta = 88.422(2) degrees, gamma = 78.454(2) degrees, V = 1450.2(5) A(3), Z = 2, R = 0.0267. The Bi in 1 is best regarded as 9-coordinate, with four short bonds to the PDALC, and two short bonds to the coordinated water molecules, with three long bonds to perchlorate oxygens. The Bi-N bonds at 2.35 A are by a considerable margin the shortest Bi-N bonds to 1,10-phenanthroline (phen) type ligands, which is suggested to be due to the Bi adapting to the metal ion size requirements of PDALC. The Th(IV) in 2 is 12-coordinate, with four bonds to PDALC, and the four chelated nitrates, with close to normal bond lengths to the PDALC ligand. The Cd(II) in 3 is 8-coordinate, with Cd-N and Cd-O bonds that are similar to those found in other 8-coordinate Cd(II) complexes. The five known structures of PDALC complexes, including the three reported here, suggest that the M-N bonds to PDALC are quite easily varied in length in response to differing metal ion sizes, but that the M-O bonds are more constrained by the rigid ligand to be close to the ideal value of 2.50 A. The formation constants (log K(1)) for M(III) ions with PDALC show that for small metal ions such as Ga(III) and Fe(III), log K(1) is only slightly higher than for phen, suggesting that these metal ions are too small to coordinate to the alcoholic oxygen donors of PDALC. For larger metal ions such as Bi(III), Gd(III), Th(IV), and UO(2)(2+), log K(1) for PDALC is higher than log K(1) for phen by more than 5 log units, which stabilization is attributed to the fact that PDALC is preorganized for complexation with large metal ions with an ionic radius of about 1.0 A. The fluorescence of M(III) complexes of PDALC is discussed. PDALC free ligand gives fluorescence typical of phen ligands, with the protonated form giving a broad less intense band, and the non-protonated form of the ligand giving an intense structured set of bands. Large lanthanide ions without partially filled f-subshells, such as La(III), Lu(III), and also Y(III), give a fairly strong CHEF (chelation-enhanced fluorescence) effect, while those with partially filled f-subshells, such as Gd(III), Yb(III), and Tb(III), strongly quench the fluorescence of PDALC. A heavy element such as Bi(III) has strong spin-orbit coupling effects that act to quench the fluorescence of PDALC almost completely, which effect is enhanced by the covalence of the Bi-N bonds.

Metal ion complexing properties of the highly preorganized ligand 2,9-bis(hydroxymethyl)-1,10-phenanthroline: a crystallographic and thermodynamic study.

Metal ion complexing properties of the ligand 2,9-bis(hydroxymethyl)-1,10-phenanthroline (PDALC) are reported. For PDALC, the rigid 1,10-phenanthroline backbone leads to high levels of preorganization and enhanced selectivity for larger metal ions with an ionic radius of about 1.0 A that can fit well into the cleft of the ligand. Structures of PDALC complexes with two larger metal ions, Ca(II) and Pb(II), are reported. [Ca(PDALC) 2](ClO 4) 2 ( 1) is triclinic, Pi, a = 7.646(3), b = 13.927(4), c = 14.859(5) (A), alpha = 72.976(6), beta = 89.731(6), mu = 78.895(6) degrees , V = 1482.5(8) A (3), Z = 2, R = 0.0818. [Pb(PDALC)(ClO 4) 2] ( 2) is triclinic, Pi, a = 8.84380(10), b = 9.0751(15), c = 12.178(2) (A), alpha = 74.427(3), beta = 78.403(13), mu = 80.053(11) degrees , V = 915.0(2) A (3), Z = 2, R = 0.0665. In 1, the Ca(II) is eight-coordinate, with an average Ca-N of 2.501 A and Ca-O of 2.422 A. The structure of 1 suggests that Ca(II) is coordinated in a very low-strain manner in the two PDALC ligands. In 2, Pb(II) appears to be eight-coordinate, with coordination of PDALC and four O donors from perchlorates bridging between neighboring Pb atoms. The Pb has very short Pb-N bonds averaging 2.486 A and Pb-O bonds to the alcoholic groups of PDALC of 2.617 A. It is suggested that the Pb(II) has a stereochemically active lone pair situated on the Pb(II) opposite the two N donors of the PDALC, and in line with this, the Pb-L bonds become longer as one moves around the Pb from the sites of the two N donors to the proposed position of the lone pair. There are two oxygen donors from two perchlorates, nearer the N donors, with shorter Pb-O lengths averaging 2.623 A. Two oxygens from perchlorates nearer the proposed site of the lone pair form very long Pb-O bond lengths averaging 3.01 A. The Pb(II) also appears to coordinate in the cleft of PDALC in a low-strain manner. Formation constants are reported for PDALC in 0.1 M NaClO 4 at 25.0 degrees C. These show that, relative to 1,10-phenanthroline, the hydroxymethyl groups of PDALC produce a significant stabilization for large metal ions such as Cd(II) or Pb(II) that are able to fit in the cleft of PDALC but destabilize the complexes of metal ions such as Ni(II) or Cu(II) that are too small for the cleft.

Metal-ion selectivity produced by C-alkyl substituents on the bridges of chelating ligands: the importance of short H-H nonbonded van der Waals contacts in controlling metal-ion selectivity. A thermodynamic, molecular mechanics, and crystallographic study.

The effect on metal-ion selectivity of the use of cyclohexenyl bridges in ligands in place of ethylene bridges is examined (selectivity is defined as the difference in log K1 for one metal ion relative to that of another with the same ligand). The syntheses of N,N'-bis(2-hydroxycyclohexyl)ethane-1,2-diamine (Cy2-en), N,N'-bis(2-hydroxycyclohexyl)propane-1,3-diamine (Cy2-tn), and 1,7-bis(2-hydroxycyclohexyl)-1,4,7-triazaheptane (Cy2-dien) are reported. The crystal structures of [Cu(Cy2-tn)(H2O)](ClO4)2 (1) and [Cu(Cy2-dien)](ClO4)2 (2) are reported. Characteristics of 1: monoclinic, Pn space group, a=11.627(2) A, b=7.8950(10) A, c=12.737(8) A, beta=98.15(3) degrees, Z=2, R=0.0524. Characteristics of 2: orthorhombic, Pbca space group, a=21.815(16) A, b=8.525(7) A, c=25.404(14) A, Z=8, R=0.0821. Structure 1 has the Cu(II) atom coordinated in the plane of the ligand to the two N donors and two O donors, with a long bond to an axially coordinated water molecule. 2 has three N donors, and one hydroxyl O donor from the ligand is coordinated in the plane around the Cu(II) atom, with the second hydroxyl O donor of the ligand occupying an axial site with a long Cu-O bond. The salient feature of both structures is the short H-H nonbonded distance between H atoms on the cyclohexenyl bridges and H atoms on the ethylene bridges of the ligand. These short contacts are important in explaining the metal-ion selectivities of these ligands. Formation constants, determined by glass-electrode potentiometry, for the Cy2-en (Cu(II), Ni(II), Zn(II), Cd(II), Pb(II)), Cy2-dien (Cu(II), Zn(II), Cd(II), Pb(II)), and Cy2-tn (Cu(II), Zn(II), Cd(II)) complexes are reported. These all show a strong shift in selectivity toward smaller metal ions compared with the analogous ligands, where ethylene bridges are present in place of the cyclohexenyl bridges of the ligands studied here. Molecular mechanics (MM) calculations are used to analyze these changes in selectivity. These calculations show that the short H-H contacts become shorter with increasing metal-ion size, which is suggested as the cause of the shift in the selectivity of ligands in favor of smaller metal ions when ethylene bridges are replaced with cyclohexenyl bridges. MM calculations are also used to rationalize, in terms of short H-H contacts, the fact that when the chelate ring contains two neutral O donors, more stable complexes result with cis placement of the donor atoms on the cyclohexenyl bridge, but with two N donors, trans placement of the donor atoms results in more stable complexes.

Direct NMR Spectroscopic Observation of a Lanthanide-Coordinated Water Molecule whose Exchange Rate Is Dependent on the Conformation of the Complexes.

A large difference in the exchange rate of the coordinated water molecule is seen in solution for the diastereoisomers M and m of a europium(III) complex with an octadentate, neutral macrocyclic ligand (kex (M)