Nenad Raos

STEREOCHEMISTRY OF COMPLEXES WITH N-ALKYLATED AMINO ACIDS. II. CRYSTAL STRUCTURE AND CONFORMATIONAL ANALYSIS OF BIS-(L-N,N-DIMETHYLISOLEUCINATO) AQUACOPPER(II)

Abstract The crystal structure of blue, orthorhombic (space group P212121) modification of bis-(L-N,N-dimethylisoleucinato)aquacopper(ii) was solved by X-ray diffraction and refined to R = 0.047. The coordination geometry around the copper atom is described by tetrahedrally distorted pyramid, with N-Cu-O angles varying from 83.4° to 97.6°. The variation in distance of Cu-O bonds (1.900 and 1.949 A) is considerably greater than the same variation of Cu-N bonds (2.014 and 2.019 A). The copper-oxygen distance (from ligated water) is 2.448 A which is significantly longer than the Cu-O bonds in chelate rings. The experimentally determined molecular structure was compared to several theoretically predicted ones by using an empirical force-field method of conformational analysis. Theoretical predictions fitted well the observed geometry of the coordination polyhedron only when non-bonding interactions with the apically ligated water molecule were taken into account.

Critical evaluation of empirical force-field models for simulation of plasticity of copper(II) coordination

Abstract The plasticity of the copper(II) coordination sphere was simulated with the empirical force-field (molecular mechanics) method. Altogether five models

Simulation of plasticity of a copper(II) coordination polyhedron with a force field based on coulombic interactions: Conformational analysis of copper(II) chelates with α-amino acids

Abstract In order to simulate the plasticity of the copper(II) coordination sphere with the empirical force-field method (molecular mechanics), a square planar complex was defined as an octahedron consisting of four charges situated in the coordination plane, and two charges above and below the plane. Between these point charges only repulsive coulombic interactions take place besides harmonic bond-stretching interactions with the central atom. The model was parametrized on tetrahedrally distorted bis( l -N, N-dimethylvalinato) copper(II) (1). The obtained force field reproduced angles around copper in both planar and non-planar copper(II)-aminoacidates with r.m.s.-deviation from 0.15 to 3.4°. The enantioselectivity effect [energy difference between Cu( l -ligand)( l -ligand) and Cu( l -ligand) ( d -ligand)] for compound 1 was reproduced within experimental error. The shape of the potential energy surface was analysed using the CuN2O2 “complex”; it yielded cis and trans conformations, but also many “false” minima. The model appears to be reliable for not too great deviations from planarity (15–30° for trans valence angles around copper).

Estimation of stability constants of coordination compounds using models based on topological indices.

Estimation of Stability Constants of Coordination Compounds using Models Based on Topological Indices The principal aim of our research was to develop theoretical models for estimating stability constants of coordination compounds, focusing on chelates of heavy metals, Cu(II) and Ni(II), with bioligands (amines, amino acids and peptides). We tried to solve the problem using graph-theoretical models. We also encountered a specific problem for coordination compounds - the choice of the constitutional formula, that is graph, of the complex species. Procjena konstanta stabilnosti koordinacijskih spojeva s pomoću modela temeljenih na topološkim indeksima Prikazani su načini rješavanja problema procjene konstanta stabilnosti bakrovih(II) i niklovih(II) kelata s aminima, aminokiselinama i peptidima primjenom graf-teorijskih modela. Osebujni problem za koordinacijske spojeve je izbor konstitucijske formule, tj. grafa kompleksnoga spoja, pa su stoga iskušani modeli temeljeni na formuli liganda i više oblika konstitucijske formule kompleksa. Pokazalo se da se najbolji rezultati postižu valencijskim indeksom povezanosti trećeg reda, 3χv. Iskušani su modeli temeljeni na kombinacijama indeksa izvedenih iz molekularnih segmenata. Takvi su se modeli pokazali osobito uspješnima za procjenu stabilnosti miješanih kompleksa.

REVIEW: THE CHEMISTRY OF CHELATES WITH N-ALKYLATED AMINO ACIDS

Abstract N-alkylated α-amino acids are compounds very suitable for studying steric effects in chelates with heavy metals, especially copper(II). These chelates are especially interesting because of pronounced stereoselective effects (enantioselectivity) as well as because of distortion of the copper coordination polyhedron. In this short review all the aspects of coordination chemistry of N-alkylated amino acids are presented and steric effects are discussed from the viewpoint of results obtained from X-ray analyses and molecular mechanics calculations.

STEREOCHEMISTRY OF COMPLEXES WITH N-ALKYLATED AMINO ACIDS. VIII. CRYSTAL STRUCTURE AND CONFORMATIONAL ANALYSIS OF AQUABIS(L-N,N-DIMETHYLTHREONINATO)COPPER(II) DIHYDRATE

Abstract The structure of blue, monoclinic (space group P21) crystals of aquabis(L-N,N-dimethylthreoninato)copper(II) dihydrate was determined by X-ray diffraction and refined to R = 0.030. The coordination around the copper(II) atom is distorted square-pyramidal with threonine N and O atoms in trans orientations (Cu-O 1.930(3) and 1.926(3)A, Cu-N 2.042(3) and 2.055(3)A, O-Cu-O 163.9, N-Cu-N 164.0°) and apical water (Cu-O(W) 2.206 A). The shape of the coordination polyhedron was reasonably well reproduced with molecular mechanics calculations, yielding root-mean-square deviations of ten valence angles around copper to 4.5°. The calculated strain energy of the crystal conformation is about 21 kJ mol− higher than the energy of the most stable conformer. This was tentatively attributed to the additional stabilization of molecular conformation by intermolecular hydrogen bonds in the solid state.

Stereochemistry of Complexes with N-Alkylated Amino Acids. v. Crystal Structure, Molecular Mechanics Calculations and Conformational Analysis of Bis(L-N,N-Diethyl-α-Alaninato)Aquacopper(II)

Abstract The crystal structure of the blue orthorhombic (space group C2221) modification of bis(L.-N,N-diethyl-α-alaninato)aquacopper was solved by X-ray methods and refined to R = 0.043. The complex has twofold crystallographic symmetry and coordination around the copper(II) atom is distorted square-pyramidal with the water molecule axial. Principal dimensions are Cu-Ow 2.260(4), Cu-O 1.922(2), Cu-N 2.075(4)A, O-Cu-O 175.6(1), N-Cu-N 159.9(2), Ow-Cu-O 92.2(1), Ow-Cu-N 100.0(1)°. The conformation of the unique chelate ring is very similar to that found in (D-N,N-diethylalaninato)(L-N,N-diethylalaninato)copper(II). The shape of the coordination polyhedron was reasonably well reproduced with theoretical calculations (molecular mechanics), yielding differences between calculated and measured angles around copper of from 1.3 to 5.2[ddot]. The calculated strain energy of the crystal conformation is about 4 kJ mol−1 higher than the energy of the most stable conformer. This fact was tentatively attributed to the...

Stereochemistry of Complexes with N-Alkylated Amino Acids. IV. Crystal Structure of Disordered D,L-BIS(N,N-Diethyl-α-Alaninato)Copper(II); Molecular Mechanics Calculations and Conformational Analysis of Copper(II) N,N-Diethylalaninates

Abstract The crystal structure of a new, red, triclinic modification of (D,L-N,N-diethyl-α-alaninato)copper(II) was solved by X-ray diffraction methods and refined to R = 0.035. The structure contains discrete molecules disordered over two sites in a 72:28 ratio with the copper atom on an inversion centre. The copper, oxygen and nitrogen atoms and one carbon atom are common to both molecules while six carbon atoms are disordered over two sites. The coordination around the copper atom is irregular square-planar with oxygen and nitrogen atoms necessarily trans. Interatomic distances [Cu-O 1.910(2)A and Cu-N 2.033(2)A] are comparable with those found in related crystal structures. The two independent molecules A and B (which are disordered about an inversion centre) have identical conformations in the lattice, molecular mechanics calculations correctly predict the crystal (most stable) conformation of D,L-bis(N,N-diethyl-α-alaninato)copper(II); the conformation predicted for the L,L isomer appears to be a tr...

Irving-Williams Order in the Framework of Connectivity Index 3χv Enables Simultaneous Prediction of Stability Constants of Bivalent Transition Metal Complexes

Logarithms of stability constants, log K1 and log β2, of the first transition series metal mono- and bis-complexes with any of four aliphatic amino acids (glycine, alanine, valine and leucine) decrease monotonously with third order valence connectivity index, 3χv, from Cu2+ to Mn2+. While stability of the complexes with the same metal is linearly dependent on 3χv, stability constants of Mn2+, Fe2+, Co2+, and Ni2+complexes with the same ligand show a quadratic dependence on 3χv. As Cu2+ complexes deviate significantly from quadratic functions, models for the simultaneous estimation of the stability constants, yielding r = 0.999 (S.E. = 0.05) and r = 0.998 (S.E. = 0.11), for log K1 and log β2, respectively, were developed only for Mn2+, Fe2+, Co2+, and Ni2+ complexes with amino acids.

STEREOCHEMISTRY OF COMPLEXES WITH N-ALKYLATED AMINO ACIDS. VII. CRYSTAL STRUCTURE OF BIS(N-tert-BUTYL-N-BENZYLGLYCINATO)COPPER(II). CONFORMATIONAL ANALYSIS AND MOLECULAR MECHANICS CALCULATIONS

Abstract The structure of the red, monoclinic modification of bis(N-tert−butyl-N−benzylglycynato)copper(II) was solved by X-ray diffraction analysis and refined to R = 0.044. The structure is made up of discrete molecules with the copper atom (situated at an inversion centre) having square-planar coordination with oxygen and nitrogen atoms in trans positions with Cu-O 187.4(2) and Cu-N 2.112(3)A. The results of molecular mechanics calculations reveal that the crystal conformation has about 13 kJ mol−1 higher energy than the lowest energy conformation. This suggests the influence of intra- and intermolecular interactions in defining the molecular conformation.