Metal Ion Complexes of N,N'-Bis(2-Pyridylmethyl)-trans-1,2-Diaminocyclohexane-N,N'-Diacetic Acid, H2bpcd: Lanthanide(III)-bpcd2- Cationic Complexes.

The synthesis and characterization of N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) cationic complexes of La(III), Nd(III), and Sm(III) are reported. The Ln(III)-bpcd2- complex ions, where bpcd2- stands for N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate, were isolated as PF6- salts. These salts were characterized by elemental analysis, X-ray crystallography, IR, and 1H and 13C NMR spectroscopy. Binuclear [La2(bpcd)2(H2O)2]2+ crystallized from an aqueous solution in the monoclinic P21/c space group as a cocrystallate with Na2bpcd and NaPF6, nominally Na2.34[La1.22(C22H26N4O4)2(H2O)2][PF6]2·2H2O, with a = 11.3343(6) Å, b = 17.7090(9) Å, c = 15.0567(8) Å, ß = 110.632(3)°, and Z = 4 (Z' = 2). La is eight-coordinate with distorted dodecahedral coordination geometry provided by a N4O4 donor atom set. In addition to four N atoms from the bpcd2- ligand, La's coordination sphere includes O atoms from a water molecule and three acetate groups (one O atom from singly bound acetate and two O atoms from acetate groups that bridge the La centers). The 1H and 13C assignments for H2bpcd and the metal-bpcd2- complexes were made on the basis of 2D COSY and HSQC experiments, which established 1H-1H and 1H-13C correlations. The NMR spectral data were used to establish the symmetry of the cationic complexes present in aqueous solution. The data indicate that the La(III)-bpcd2- and Sm(III)-bpcd2- complexes are present in solution as a single species with C2 symmetry. The 1H NMR spectrum of [Nd(bpcd)]PF6 in D2O consists of eight considerably line-broadened, paramagnetic-shifted singlets. The ab initio quantum mechanical calculations at the PCM/MP2/SDD//HF/SDD level, which were established previously for determining isomerization energies for octahedral M(III)-bpad2- complex ions, were used to determine the relative free energies of the geometric isomers possible for eight- and nine-coordinate La(III)-bpcd2- cationic aqua complexes in aqueous solution, i.e., [La(bpcd)(H2O)2]+ and La(bpcd)(H2O)3]+.

Metal Ion Complexes of N,N'-Bis(2-Pyridylmethyl)-trans-1,2-Diaminocyclohexane-N,N'-Diacetic Acid, H2bpcd: Cis/Trans Isomerization Equilibria.

The synthesis of N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) and its complexation of Ga(III) and Co(III) are reported. H2bpcd and the metal-bpcd(2-) complexes, isolated as hexafluorophosphate salts, were characterized by elemental analysis, X-ray crystallography, IR spectroscopy, and (1)H and (13)C NMR spectroscopy. [Ga(bpcd)]PF6, [Ga(C22H26N4O4)]PF6, crystallized in the orthorhombic space group Ibca, with a = 13.8975(7) Å, b = 15.0872(7) Å, c = 22.2418(10) Å, and Z = 8. Ga is coordinated in a distorted octahedral geometry provided by a N4O2 donor atom set with trans-monodentate acetate groups and cis-2-pyridylmethyl N atoms, i.e., the trans-O,O isomer. The diamagnetic [Co(bpcd)]PF6, [Co(C22H26N4O4)]PF6, also crystallized from solution in the Ibca space group as the trans-O,O isomer. The (1)H and (13)C assignments for H2bpcd and metal-bpcd(2-) complexes were made on the basis of 2D COSY and HSQC experiments, which were used to differentiate among three possible isomers, i.e., one cis (C1 symmetry) and two trans (C2 symmetry). NMR results indicate that the [Ga(bpcd)](+), [Co(bpcd)](+), and cis-O,O, cis-Npy,Npy-[Ga(bppd)](+) cations, where bppd(2-) stands for bis(2-pyridylmethyl)-1,3-diaminopropane diacetate, are present in solution as isomers with the same symmetry as observed in the solid state. The crystallographic data and the dramatic shift that occurs in the position of the cis/trans isomerization equilibria for the [Ga(bpad)](+) cations simply by increasing the number of bridging CH2 groups in the ligand's diamine backbone represent a unique opportunity to assess the accuracy of modern computational methods. The performance of several local density functionals using a pseudopotential-based SDD basis set was compared with the more rigorous HF and MP2 ab initio calculations. The SVWN5 and SV5LYP functionals provide significantly better Ga-O and Ga-N distances than the HF method or the nonlocal BLYP functional. However, to provide proper isomerization energies the pseudopotential-DFT calculations must be augmented by MP2 single-point energies and calculations of solvation free energies.

Crystal structure of {2,2'-[N,N'-bis-(pyridin-2-yl-meth-yl)cyclo-hexane-trans-1,2-diyldi(nitrilo)]di-acetato}-cobalt(III) hexa-fluorido-phosphate.

The title compound [Co(C22H26N4O4)]PF6, commonly known as [Co(bpcd)]PF6, where bpcd(2-) is derived from the historical ligand name N,N'-bis-(2-pyridyl-meth-yl)-trans-1,2-di-amino-cyclo-hexane-N,N'-di-acetate, crystallized by slow evaporation of a saturated aceto-nitrile solution in air. The cation of the hexa-fluorido-phosphate salt has the Co(III) atom in a distorted octa-hedral coordination geometry provided by an N4O2 donor atom set. The acetate groups, which are oriented trans with respect to each other, exhibit monodentate coordination whereas the pyridyl N atoms are coordinating in a cis configuration. The geometry of the cation is compared to the geometries of other di-amino di-acetate complexes with Co(III).

Metal ion complexes of N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane-N,N'-diacetic acid, H2bppd.

A higher yield synthesis of N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane-N,N'-diacetic acid (H2bppd) and its complexation of trivalent metal ions (Al(III), Ga(III), In(III)) and selected lanthanides (Ln(III)) are reported. H2bppd and the metal-bppd(2-) complexes, isolated as hexafluorophosphate salts, were characterized by elemental analysis, mass spectrometry, IR, and (1)H and (13)C NMR spectroscopy. [Ga(bppd)]PF6, [Ga(C19H22N4O4)]PF6, was crystallized as colorless needles by slow evaporation from anhydrous methanol; its molecular structure was solved by direct X-ray crystallography methods. The compound crystallized in the monoclinic space group P21/c, with a = 9.6134(2) Å, b = 20.2505(4) Å, c = 11.6483(3) Å, ß = 97.520(1)(o), and Z = 4. Ga is coordinated in a distorted octahedral geometry provided by a N4O2 donor atom set with cis-monodentate acetate groups and cis-2-pyridylmethyl N atoms. Quantum mechanical calculations were performed for the three possible geometric isomers of a pseudo-octahedral metal-bppd(2-) complex with five different metal ions. The results indicate, that in aqueous solution, the stability of the trans-O,O isomer is similar to that of the cis-O,O; cis-Npy,Npy isomer but is greater than that of the trans-Npy,Npy isomer. Calculations for a six-coordinate La(III)-bppd(2-) complex converge to a structure with a very large Npy-La-Npy bond angle (146.4°), a high metal charge (2.28 au), and a high solvation free energy (-79.4 kcal/mol). The most stable geometric arrangement for bppd(2-) around the larger La(III) is best described as an open nestlike structure with space available for additional ligands. IR spectroscopy was used to investigate the nature of the H2bppd-metal complexes isolated in the solid state and the binding modes of the carboxylate functionalities. The spectra indicate that fully deprotonated [M(bppd)](+) complexes as well as partially protonated complexes [M(Hbppd)Cl](+) were isolated. The (1)H and (13)C assignments for H2bppd and metal-bppd(2-) complexes were made on the basis of 2D COSY, NOESY, and (1)H-(13)C HSQC experiments, which were used to differentiate among the cis (C1 symmetry) and the two trans (C2 symmetry) isomers.

{2,2'-[N,N'-Bis(pyridin-2-ylmeth-yl)propane-1,3-diyldi(nitrilo)]di-acetato}-cobalt(III) hexa-fluoridophosphate aceto-nitrile 0.064-solvate.

In the title compound, [Co(C19H22N4O4)]PF6·0.064CH3CN, commonly known as [Co(bppd)]PF6·0.064CH3CN, where bppd represents the historical ligand name N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane-N,N'-diacetate, the Co(III) atom is coordinated in a distorted octa-hedral geometry with an N4O2 donor atom set. The acetate O atoms, which exhibit monodentate coordination, are oriented in a trans configuration with respect to each other, whereas the pyridyl N atoms are coordinated in a cis configuration. The compound crystallizes with two crystallographically unique cations and two anions per asymmetric unit along with a disordered, partially occupied (occupancy = 0.128) aceto-nitrile solvent mol-ecule. Crystals of the title complex were found to be twinned by pseudomerohedry with a 180° rotation around [10-1] and a refined contribution of 90.5 (3)% of the major twin component.

Alkaline phosphatase inhibition by vanadyl-beta-diketone complexes: electron density effects.

A series of systematically modified vanadyl-beta-diketone complexes, VO(beta-diketone)(2), bearing substituent groups with different electron inductive properties were synthesized and evaluated as inhibitors against calf-intestine alkaline phosphatase (APase). A combination of biochemical and quantum mechanical techniques were employed to identify structure-activity relationships relevant for rational design of phosphatase inhibitors. Kinetic parameters and activation free energy, enthalpy, and entropy for calf-intestine APase-catalyzed dephosphorylation of para-nitrophenylphosphate were also determined along with the inhibition constants (K(i)) for the VO(beta-diketone)(2) complexes. Increased positive charge on the vanadyl group increases the inhibition potency of the complex while the absence of an available coordination site on the complex decreases its inhibition potency. These findings correlate well with the results of ab initio electron density calculations for the complexes.

SYNTHESIS OF SYMMETRICAL METHYLENEBIS(ALKYL HYDROGEN PHOSPHONATES) BY SELECTIVE CLEAVAGE OF METHYLENEBIS(DIALKYL PHOSPHONATES) WITH MORPHOLINE.

The preparation of partial esters of methylenebisphosphonic acids has been of recent interest due to their potential therapeutic applications. This paper describes a convenient method to prepare symmetrical methylenebis(alkyl hydrogen phosphonates) by the selective cleavage of the corresponding methylenebis(dialkyl phosphonate) with refluxing morpholine. The effects of structural variations on the amine as well as the substrate have been investigated to understand the scope and limitations of this reaction. A superior approach to hindered bisphosphonic acid esters involves the cleavage of their dimethyl esters, 4, using morpholine. This method is also useful to access a number of C-alkyl dialkyl methylenebisphosphonic acids such as 6. This study clearly shows that cleavage with morpholine is convenient, inexpensive, and allows for the preparation of a variety of P,P'-disubstituted partial esters in good yields and high purity.