Najeeb A. Al-Salem

A new series of 1D polymeric nickel(II) complex cations of pyridine derivative ligands with a single μ-1,3 azide bridge and X-ray crystal structure and magnetic properties of polymeric {[Ni(4-ethylpyridine)4(N3)n](PF6)n}

A new series of polymeric nickel(II) complex cations of the formula [NiL 4 (N 3 )](PF 6 ), for L = pyridine, 4-methyl-, 4-ethyl-, 3-chloro-, 3-bromo- and 3-hydroxy-pyridine, have been prepared and characterized. Solid state electronic spectra suggest six-coordinate nickel(II) in all complexes. IR spectral results reveal the existence of symmetrical azido ligands and PF 6 - counter ions in these complexes. X-ray crystal structure determination has shown the complex for L = 4-ethylpyridine (1) to contain a polymeric [NiL 4 (N 3 )] + cation and PF 6 -, anions. In the cation each nickel(II) atom is coordinated by four nitrogen atoms from the pyridine ligands and two nitrogen atoms each from a μ-1,3 bridging azide giving rise to ID polymeric chains of six-coordinate Ni(II) polyhedra. The azide ligand is symmetrical [N 1 - N 2 =N 2 -N 3 = 1.152 and N 1 -N 2 = 1.164, N 2 -N 3 = 1.162 A] and linear [NNN angles =178° and 180°] within the experimental error. The magnetic susceptibilities of 1 in the range of 2-300 K, have been measured and discussed.

Complexes of vitamin B6. XVII: Crystal structure and molecular orbital calculations of the dichloro-bis-pyridoxol palladium (II) complex

Abstract The structure of dichloro-bis-pyridoxol palladium(II) complex [PdCl2(C8H11O3N)2] has been determined from three dimensional X-ray data collection. The complex crystallizes in the monoclinic space group P21/c with Z=2 and cell dimensions a=5.265(3), b=17.250(6), c=10.253(6) A, β= 95.40(2)°. The structure was refined to a final R factor of 0.060 for 1813 reflections with F ⩾ 3σ(F). The palladium atom lies in a symmetry center of inversion in a square plane coordinated to two chlorine atoms and two pyridine nitrogen atoms. Charge distributions and bond order matrix calculated from ARCANA-MO are given.

A copper(II) azide compound of pyrazinic acid containing a new dinuclear complex anion [Cu2(N3)6]2−. Synthesis, spectral and study of KCu2(pyrazinato) (N3)4

Abstract A new complex of copper(II) azide with pyrazinic acid, of general formula KCu2(pyrazinato)(N3)4 has been synthesized and characterized by spectroscopic and crystallographic methods. The structure of the complex consists of a new dinuclear complex anion [Cu3(N3)6]2−, potassium cations and neutral polymeric complex [Cu(pyrazinato)(N3)]. Each distorted square-planar copper centre [Cu(1)] in the complex anion is coordinated to four nitrogen atoms from two terminal and two μ-(1,1) bridging azido ligands [CuN distances 1.940(6)–2.011(5) A]. In the polymeric complex, each copper atom, Cu(2), is coordinated to N(41) of a terminal azido group and N(61), N(62) and O(31) from pyrazinato anions to form infinite, “neutral” chains of polyhedra with orientations along [010]. The potassium cations are located in broad channels which are a consequence of stacking of the copper complexes. The IR spectrum confirms the presence of different asymmetric azido ligands. The absorption frequencies of diagnostic values are given and discussed. The electronic spectrum displays three absorption bands associated with N3−CuII charge transfer transitions. The EPR spectrum of the solid complex suggests an axial structure with non-coupled copper(II) atoms.

Synthesis, spectral and structural characterization of two polymeric 1:1 complexes of 2,3-dimethylpyridine and 5-ethyl-2-methylpyridine with copper(II) azide; Cu(2,3-dimethylpyridine) (N3)2 and Cu(2-methyl-5-ethylpyridine) (N3)2

Abstract Two new 1:1 ligand complexes of copper(II) azide with disubstituted pyridine ligands, namely catena-di-μ(1,3)-azido-[di-μ(1,1)-azidobis(2,3-lutidine)dicopper(II)] (1) and catena-di-μ(1,1)-azido[di-μ(1,1)-azidobis(2-methyl-5-ethylpyridine)dicopper(II)] (2), have been synthesized and characterized by spectroscopic and X-ray crystallographic methods. The polymeric complex 1 features monodentate 2,3-lut ligands, centrosymmetric di-μ(1,1)-azido-bridged Cu2N2 rings, distorted square-pyramidal copper(II) coordination geometry and di-μ(1,3)-azido bridges which link the centrosymmetric binuclear Cu2(2,3-lut)2(N3)2 moieties to form sheets within the ab plane. In the monoclinic crystals of complex 2, the copper(II) centres are pentacoordinated via N(11), N(21), N(11b) and N(21a) from the azido ligands [CuN distances 1.971(5)–2.286(5) A] and N(1) from the organic molecule at a CuN bond length of 2.001(5) A. Both azido ligands function as μ(1,1) bridges to form chains of polyhedra along the short a-axis of the unit cell. The IR absorption spectra reveal that each of these complexes contains two independent azide ligands. The solid and solution electronic spectra of complexes 1 and 2 show at least three and two strong absorption bands, respectively, associated with N3− → CuII charge transfer transitions. The EPR spectra of powder samples and DMSO solutions at room temperature were recorded and are discussed.

A POLYMERIC COMPLEX OF MANGANESE(II) AZIDE CONTAINING ALTERNATE END-ON AND END-TO-END BRIDGING AZIDO LIGANDS Synthesis, Structural, Spectroscopic and Thermal Study of [Mn(N3)2 (Ethyl Nicotinate)2]n

Abstract A mixed ligand 1:2 manganese(II) azido complex of ethyl nicotinate has been synthesized and characterized by spectroscopic and crystallographic methods. The structure consists of a two-dimensional manganese-azido compound with each manganese atom in a trans octahedral environment, bonded to four azido ligands [Mn−N = from 2.199(4) A to 2.231(3) A] and two axial ethyl nicotinate ligands [Mn-N = 2.285(3) and 2.308(3) A]. Two azido ligands are coordinated end-on between the manganese atoms giving planar and centrosymmetric Mn2N2 units. Each Mn2N2 unit is linked to four neighboring Mn2N2 units by means of four end-to-end azido bridges. The IR and Raman spectra correlate with the structure of the complex. The vibrational bands are compared with those of the free ligand. The EPR spectra of polycrystalline powder and solutions of the complex are measured at room temperature and discussed. The thermal decomposition of the complex was investigated derivatographically under nitrogen.

Synthesis and characterization of cobalt(III) azido complexes of some disubstituted pyridine ligands and X-ray crystal structure of mer-[Co(3,4-dimethylpridine)3(N3)3] and mer-Co(3,5-dimethylpyridine)3(N3)3]

Abstract Cobalt(III) azido complexes of some disubstituted pyridine ligands of the type CoL3(N3)3 have been prepared and characterized. The complexes gave non-conducting solutions and their solid state and solution electronic spectra are discussed. The IR spectra reveal the asymmetric nature of the azido ligands and the mer-formulation was confirmed by the number of Co—N(N3 and Co—N(L) stretching bands observed in the far-IR region. X-ray crystal structure determinations were done for mer-[Co(3,4-dimethylpyridine)3(N3)3] (1) and mer-[Co(3,5-dimethylpyridine)3(N3)3] (2). Both compounds contain discrete molecules with approximately octahedral cobalt(III) ion. The Co—N(N3) distances are variable from 1.931(4) to 1.959(4) A and from 1.944(3) to 1.965(3) A whereas Co—N(L) bond lenghts are from 1.955(3) to 1.994(3) and from 1.973(3) to 1.990(3) A for 1 and 2, respectively. The thermal decomposition of complexes (1) and (2) were investigated drivatographically in nitrogen. Complex (1) explodes completely in one step at 175°, whereas complex (2) loses one 3,5-DMPy molecule and an azide ion in the first step around 139° and then explodes at 172°.

Synthesis, spectral and structural characterization of [NaMn(Pyrazinato)(NCO)2(H2O)2], a polymeric structure containing μ(O,O,N)-bridging cyanato ligands between manganese and sodium-centred polyhedra

Abstract The complex [NaMn(pyrazinato)(NCO) 2 (H 2 O) 2 ] has been synthesized and characterized by spectroscopic and X-ray crystallographic methods. The infrared and Raman spectral results suggest that the complex contains a N,O-bidentate pyrazinato anion, aqua ligands and Mn-O bonded cyanato groups. The structure of the complex features an octahedrally coordinated manganese atom as well as six-coordinated sodium atom. Each manganese atom is chelated by a pyrazinato anion [via its ring nitrogen atom, Mn-N = 2.320(4) , and a carboxylato oxygen atom, Mn-O = 2.175(3) ], and links a bridging aqua ligand [Mn-O = 2.284(3) ] and three μ(O,O,N)-bridging cyanato ligands [Mn-O from 2.144(4) to 2.307(4) ]. The sodium atom is bonded to three bridging cyanato groups in a facial arrangement [Na-N(13) = 2.340(5) , Na-N(23) = 2.368(4) , and Na-O(11) = 2.584(4) ] and three water molecules [Na-O av. = 2.421 ] in which two of them act as bridges between two sodium octahedra. The manganese and sodium octahedra have a common edge via an aqua ligand and a cyanato group.

Polymeric complexes of copper(II) azide and 2,5-dimethylpyridine without and with solvent molecules. Synthesis, spectral and structural characterization of [Cu(2,5-dimethylpyridine) (N3)2]n and [Cu(2,5-dimethylpyridine) (N3)2(H2N-CHO)]2

Abstract Catina di-μ(1,1)-azido[di-μ(1,1)-azidobis(2,5-dimethylpyridine)dicopper(II)] (1) and di-μ(1,1)-azidobis[azido(2,5-dimethylpyridine)(formamide)]dicopper(II) (2) were synthesized and characterized by spectroscopic and crystallographic methods. In the triclinic complex 1 the copper(II) centres are penta-coordinated by four nitrogen atoms from the azido ligands [CuN distances = 1.980(3)-2.249(4) A] and a fifth nitrogen from the organic molecule at a CuN bond length of 2.038(4) A. Both azido ligands function as μ(1,1) bridges to form chains of polyhedra along the crystallographic a axis. The dimeric molecule 2, which possesses a crystallographic inversion centre, contains both terminal and μ(1,1) bridging azido ligands. Each copper(II) atom is further coordinated by a 2,5-dimethylpyridine molecule [ Cu  O = 1.998(4) A ] and a formamide molecule via its carbonyl oxygen atom [ Cu  O = 2.356(4) A ] to give a distorted square pyramid. The IR absorption spectra reveal asymmetric azido ligands in both complexes, O-bonded formamide and hydrogen bonds as well, in 2. The solid and solution electronic spectra of both complexes exhibit more than one strong N3− → CuII charge-transfer transition band. The room-temperature EPR spectra of powdered samples and DMF solutions were recorded and discussed.

Hydrated manganese(II) cyanato complexes of 3- and 4-acetyl, carbomethoxy-, carboethoxy- and benzoylpyridine derivative ligands and crystal structure of trans-dicyanato-bis(4-acetylpyridine)diaquamanganese(II); [Mn(4-acetylpyridine)2(NCO)2(H2O)2]

Abstract A series of 1 : 2 manganese(II) cyanato complexes of 3-, 4-acetyl-, 3- and 4-benzoylpyridine, methyl and ethyl nicotinate and isonicotinates has been prepared and characterized. Except for L = ethyl isonicotinate, all other complexes crystallize with two water molecules. In the case of ethyl isonicotinate the complex crystallizes with two ethanol molecules. the IR and Raman spectral lines of diagnostic value are given and discussed, suggesting terminal N-bonded cyanato ligands and aqua molecules or bonded ethanol molecules in these manganese(II) complexes. The structure of [Mn(4-acetylpyridine)2(OCN)2(H2O)2] as determined by crystallographic methods features six-coordinated manganese(II) centres, pairs of trans aqua molecules [ Mn  O = 2.202(3) A ] , N-bonded cyanato ligands [ Mn  N = 2.116(3) A ] and monodentate N-bonded carbonyl pyridine ligands [ Mn  N = 2.322(3) A ] . The structure is further consolidated by hydrogen bonds between aqua oxygen atoms of acetyl groups or terminal oxygen atoms of cyanato ligands. These hydrogen bonds connect the polyhedra along the cb plane to form a layer-type structure. The EPR spectra of powder samples and solvent solutions at room temperature were recorded and discussed.

Palladium complexes with biological ligands-I. Equilibrium and reaction mechanism of Pd(II) complexes with ethionine

Abstract An equilibrium study has been carried out on the interaction of ethionine(eth) with Pd(II) in aqueous solution at I = 0.16 M (Cl− and 25°C using potentiometic methods. It has been concluded that five complex species exist in the pH range 2.8–4.8. these species are: PdCl3(Eth0H02, PdCl2(Eth)−, PdClOH(Eth)−, Pd(Eth)2(H)2+2 and Pd(Eth)02. In addition, the stopped-flow method has been used to study the reaction kinetics of Pd(II) with Eth. Three kinetic steps were observed in the pH range 1–5.5. These steps are dependent on the total concentration of Eth (TEth) as well as the pH of the medium. The observed pseudo-first order rate constants for the three reaction kinetic steps at constant pH are expressed empirically by kiobs = mi + m′iTEth. The parameters mi and m′i are pH-dependent. It has been concluded that PdCl2−4 and PdCl2OH2− species play an important role in the complex formation reactions with Eth. The data were interpreted in terms of the complex species obtained from the equilibrium study. cis-trans substitution reactions have been suggested to account for some kinetic steps.