G.St. Nikolov

Electronic spectra of diethyldithiocarbamate complexes of central atoms with closed-shell configurations

Abstract The electronic spectra of a number of diethyldithiocarbamate complexes of elements with closed-shell configurations have been recorded in different solvents. The observed transitions are discussed in terms of solvent shift and valence orbital energy differences. The u.v. bands of the ligand ( ca. 35 and 39 kK), slightly affected by the presence of the central atom, are present also in the spectra of all the complexes. These bands are essentially intraligand transitions. The results indicate that the high energy band ( ca. 39 kK) is connected with a transition located in the CS 2 group of the ligand. It is suggested that this band is sensitive to the type of coordination.

The crystal and molecular structures of (diethylenetriamino)copper(II) nitrate

Abstract The blue needle-like (H 2 NCH 2 CH 2 NHCH 2 CH 2 NH 2 )Cu(NO 3 ) 2 or Cu(dien)(NO 3 ) 2 for short was studied by X-ray diffraction, magnetic measurements, infrared and electronic spectra, and electric conductivity. It crystallizes in the space group Pmnb with Z =4 and a =9.050(4), b =9.066(4), c =12.944(4) A, V =1062.0 A 3 and D x = 1.818 g cm −3 . The symmetry plane contains the Cu atom, one NO 3 − group (asymmetric bidentate and bridging, CuO1=2.13 A, CuO2=2.56 A), the dien NH group (CuN=1.99 A) and an intermolecular contact with the neighbouring bridging NO 3 − group (CuO2″=2.29 A). The two terminal NH 2 groups provide almost linear (∢NCuN′=169°) out-of-plane CuN bonds (1.994 A long). Viewed down the intermolecular contact, parallel to the symmetry plane, Cu is five-coordinate in a distorted square pyramidal (with O2″ in the apical position) arrangement or a distorted trigonal pyramid with N, N′ apical contacts. The second (uncoordinated) NO 3 − group is hydrogen bonded to dien. Magnetic and solid state spectral data are in agreement with this molecular structure. Solution spectra, however, and electric conductivity data indicate a monomeric Cu(dien)(NO 3 ) + unit with a four-coordinate Cu atom.

Diethyldithiocarbamate complexes of tellurium(II) and tellurium(IV)

Abstract Solution spectra of diethyldithiocarbamate complexes of tellurium(II) and (IV), Te(dtc)2 and Te(dtc)4, have been recorded. Spectral evidence suggests that both the dtc ligands of Te(dtc)2 are unidentate, and that two of the dtc ligands of Te(dtc)4 are unidentate, and the other two bidentate. Thus tellurium in Te(dtc)4 is in a distorted octahedral environment, while the STeS angle in Te(dtc)2 is probably near to 90°.

Crystal and molecular structures of [(2-amino-5-methyl-1,3-thiazole)(1,4,7-triazaheptane)copper(II)] dinitrate

Abstract The reaction of (1,4,7-triazaheptane)Cu(NO3)2 with 2-amino-5-methyl-1,3-thiazole (amtz) yields the compound [(amtz)(dien)Cu](NO3)2 (dien=1,4,7-triazaheptane). The compound has been characterised by elemental analyses, molar conductance and magnetic measurements, as well as by its electronic and IR spectra and X-ray diffraction. There are two crystallographically discernible cations [(amtz)(dien)Cu]2+ and four NO3− in the asymmetric unit of the structure. Dien is tridentate with mean Cu–N=1.997(5) and 2.021(5) A in the two Cu-ions, respectively. Amtz is coordinated through its endocyclic N with Cu–N=2.063(7) and 1.945(6) A in the two ions, respectively. The CuN4 unit is approximately square planar and almost perpendicular to the tz plane. Both the cations make two long (trans-Cu…O=2.6–2.7 A) contacts. Ab initio calculations on the constituent fragments [(dien)Cu]2+, [(amtz)Cu]2+ and [(dien)(amtz)Cu]2+ reproduced the average molecular structure parameters of the two Cu-ions in the unit cell and also helped interpret the details of the molecular structure as well as the assignment of the vibrational and electronic spectra.

Spectra and bonding of diethyldithiocabamate complexes. III. hte electronic spectra of complexes of trivalent open-shell central atoms

Abstract The electronic spectrs of tris(diethyldithiocarbamato) complexes of central atoms with open-shell configurations are discussed in terms of central atom (dd) and electron transfer transitions. The splitting and the electronic repulsion parameters obtained from the d  d spectra are used to calculate the energies of the charge transfer bands using a method described by Jorgensen. It is shown that the complexes of Cr III , Fe III , Rh III and Ru III are nearly octahedral, while ffor Mn III and partially for Co III , deviations from octahedral symmetry are reflected in the electronic spectra. The spectrum of the Fe III complex consists of abnds of both the low- and high-spin species. the optical electronegativity of the diethyldithiocarbamate ligand is found to be 2.5.

Crystal, molecular, electronic and vibrational structures of di-μ-thiocyanato-bis-[di-(3-aminopropyl)amine]-dicopper(II) diperchlorate

The crystal and molecular structures of the dimeric [Cu(dpta)(NCS)(ClO4)]2. (dpta=di(3-aminopropyl)amine) have been reinvestigated by X-ray diffraction. The crystals are orthorhombic, space group Pbca with a = 13.938(3), b = 12.424(3), c = 15.864(2) A, V = 2747(1) A3and Z = 4. The structure was refined to R = 0.050 (Rw = 0.049) from 1742 observed unique reflections. Each Cu atom is coordinated to the 3 N atoms of a dtpa ligand and to the N atom of an NCS− group in an almost square planar arrangement. The Cu atom makes further axial contacts with the S atom of another [Cu(dpta)(NCS)]+ unit and with one O atom of a ClO4− group thus forming a centrosymmetric dimeric unit [(dpta)CuSCNNCSCu(dpta)]2+. Such units are held together by the ClO4− ions which provide CuO contacts and H bonds to neighbouring dpta H atoms. The ultimate arrangement around Cu may be described as a strongly elongated octahedron. The bond lengths (in A) are: CuN(primary amine) =1.999(6) and 2.012(6), CuN(secondary amine) = 2.052(5), CuN(NCS) = 2.000(6), CuS = 2.795(2), CuO = 2.93(1). Considering the plane of the two bridging NCS groups as equatorial, the dpta ligand is in a meridional position with chair-chair conformation in full agreement with molecular mechanics calculations. Chair-skew boat conformers, however, are predicted to lie close in energy. The IR and Raman spectra of the compound were assigned by normal coordinate analysis and MNDO calculations. The bands 855 (R), 890 (IR) and 980 (IR + R) cm−1 are typical for mer-coordinated dpta and can be used as a diagnostic tool to detect the ligand coordination mode.

Molecular mechanical and quantum chemical study on the species involved in the hydrolysis of cis-diamminedichloroplatinum(II) and substituted bis(ethylenediamine)dichloroplatinum(II) complexes Part I. Reactants and products

Cisplatin and its substituted ethylenediamine derivatives, cis-PtCl2(R2en) (en=ethylenediamine, R=H, Ph (phenyl), 2-, 3- and 4-PhOH) have been studied with respect to the first step of their hydrolysis reaction. The geometry of the reactants and products was determined by molecular mechanics (MM). The MM optimized structures were used to calculate by the extended Huckel method the charge distribution and relative electronic energies. The MM and EH calculations were carried out with different ligand conformations. Due to increased non-bonded repulsion, with increasing ligand buikiness, the square planar arrangement is the preferred geometry also by the MM results. This additional (to the electronic) stabilization of the square planar arrangement around Pt(II) is unfavorable for the aquation process. The thermodynamic stabilities correlate with the rate of hydrolysis of meso-, (+)- and (−)-[1,2-bis(2-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (3-PtCl2). The slower rate of hydrolysis of the meso diastereoisomer as compared with that of the d, l species of 3-PtCl2 is explained by the presence of a 5th Pt-O contact in the meso diastereoisomer which hinders the entrance of the water molecule and makes the hydrolysis slower.

Molecular structures and infrared spectra of five-coordinate copper(II) complexes including one tridentate diethylenetriamine ligand

Abstract The molecular structures of five-coordinate Cu(dien)L2 (dien = diethylenetriamine; LNO3−, Br−, Cl−, ClO4−) have been examined by molecular mechanics (MM2). All compounds have dien in the meridional (mer) position and k,k′ (symmetric) conformation. The dien position, however, differs from the rigorous mer form as to the NCuN (N-terminal) being less than the expected 180°. The IR bands of these compounds in the 50–4000 cm−1 range have been recorded in the solid state and assigned on the basis of normal coordinate analysis (potential energy distribution) of the dien molecule. The experimental IR spectra of the studied compounds were compared with frequencies calculated by the MOPAC 6.0 package assuming dien to be coordinated in fac and mer positions. The comparison shows that in fact the dien ligand in the studied compounds should be midway between the fac and mer positions.

Normal coordinate analysis of the dithiocarbamate ligand and bis-(N,N-diethyldithiocarbamate)nickel(II), copper(II), zinc(II) and cadmium(II)

Abstract The vibrational frequencies of H 2 NCS 2 − (H 2 dtc), Et 2 dtc − , and M(Et 2 dtc) 2 (M = Ni, Cu, Zn, Cd) have been calculated by performing normal coordinate analysis using Gribovs fragmentation procedure within the generalized valence force field approximation. The force field resulting from the experimental frequencies shows a high degree of mixing between the different parts of the molecules. The fragmentation approach has allowed a detailed assignment of the observed frequencies even in the highly correlated force field.

Redox reactions of metal ions. II. Correlations of reagent electronic structure parameters with reaction rates

Abstract Correlations between activation energy and basicity constants of the reductants are found for a number of redox reactions proceeding with metal ions as oxidants. Two types of correlation equations are found giving a possibility for discerning between weak and strong type of interaction of the reactants in the activation state. The activation energy is found to depend also or the energy of the reduction for a series of reactions with one and the same oxidant.