Boris-Marko Kukovec

Preparation and structural, spectroscopic, thermal, and electrochemical characterizations of iron(III) compounds containing dipicolinate and 2-aminopyrimidine or acridine

Two new iron(III) compounds, (Hamp)[Fe(pydc)2] · 2H2O (1) and (Hacr)[Fe(pydc)2] · 2H2O (2) (pydc2− = pyridine-2,6-dicarboxylic acid, amp = 2-aminopyrimidine, acr = acridine), have been hydrothermally synthesized. Both compounds were characterized by spectroscopic methods (IR, UV/Vis), and their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stability by thermogravimetric analysis/differential thermal analysis (TGA/DTA) methods. Compound 1 consists of Hamp+ cation and [Fe(pydc)2]− anion and 2 consists of Hacr+ cation and [Fe(pydc)2]− anion. Crystallographic characterization revealed an octahedron as a coordination polyhedron for the complex anion in 1 and 2 and the same O,N,O′-chelated coordination mode of pyridine-2,6-dicarboxylate. The crystal structures of 1 and 2 are stabilized by a complicated network of hydrogen bonds between the crystallization water molecules, counter ion, and carboxylates of pydc2−. Thermogravimetric (TG) analyses of the two compounds were carried out to examine their thermal stabilities. Cyclic voltammetric response of bare glassy carbon electrode surface in 0.10 mol L−1 phosphate buffer containing 1 and 2 at different pH values indicated that they have the same voltammograms at all pH values and the electrochemical behavior of 1 and 2 has not been affected by different ion pairs. The formal potential of the solutions of 1 and 2 at the glassy carbon electrode surface was also pH-dependent with a slope of −57.0 mV/pH unit at 25°C. This shows that the number of electrons and protons involved in the electrode process is equal.

Synthesis and characterization of copper(II) complexes with 3-methylpicolinic acid. Crystal and molecular structure of bis (3-methylpicolinato- N , O )(4-picoline)copper(II)

Copper(II) complexes of 3-methylpicolinic acid (3-MepicH), namely [Cu(3-Mepic)2] · 2H2O (1) and [Cu(3-Mepic)2(4-pic)] (2) were prepared and characterized by IR spectroscopy and thermal analysis (TGA/DTA). Crystal structure for 2 was determined by X-ray crystal structure analysis. 1 was prepared by reaction of copper(II) sulfate pentahydrate and 3-methylpicolinic acid in aqueous solution, while 2 was prepared by recrystallization of 1 from 4-picoline solution. Structure analysis revealed square-pyramidal copper(II) coordination and N,O-chelating mode of 3-methylpicolinic acid in 2. Copper(II) is coordinated by two 3-Mepic ligands in the basal plane of a square pyramid and by 4-picoline in the apical position. Crystal packing of 2 is dominated by weak intermolecular C–H ··· O hydrogen bonds and π ··· π stacking interactions forming a complex three-dimensional supramolecular architecture.

Preparation and Crystal Structure of Lead (II) Complex with Propane-1,2-Diamine

The reaction of propane-1,2-diamine (pdam) with lead (II) nitrate in the ethanol solution led to the formation of a lead (II) complex, [Pb(NO3)(pdam)2]NO3 (1), with interesting coordination environment of the lead (II) ion. The compound was characterized by elemental analysis and IR spectroscopy and its crystal structure was determined by single crystal X-ray structural analysis. Lead (II) ion is coordinated by two neutral N,N′-bidentate propane-1,2-diamine ligands and by an O,O′-bidentate nitrate ion in a complex cation of 1. There is also an uncoordinated nitrate ion as counter-ion. The primary coordination sphere around lead (II) ion includes four N atoms (Pb–N, 2.377(4)–2.644(4) Å). The effective coordination around lead (II) ion could be described as a highly distorted octahedron if the Pb···O contacts (Pb1···O4, 3.090(4) Å, Pb1···O5, 3.177(3) Å) are included. The coordination polyhedron is better described as a distorted pentagonal pyramid due to the presence of stereochemically active lead (II) ion lone pair of electrons in the axial position of the pyramid. Thus, the complex is hemidirected. Complex cations and nitrate counter-ions are connected into 3D structure by hydrogen bonds of the N–H···O type.Graphical AbstractLead (II) complex with propane-1,2-diamine (pdam), [Pb (NO3) (pdam)2] NO3, was characterized by elemental analysis and IR spectroscopy and its crystal structure was determined by single crystal X-ray structural analysis.

2D s-d Mixed-Metal Coordination Polymer Containing Potassium, Chromium(III) and Dipicolinate Ions: Preparation and Crystal Structure

The reaction of pyridine-2,6-dicarboxylic acid (dipicolinic acid, dipicH2) with potassium tetraperoxochromate(V) in the mixture of water and ethanol led to the formation of a 2D s-d mixed-metal coordination polymer of {K[Cr(dipic)2]}n (1). The compound was characterized by spectroscopic methods (IR, Raman, UV/Vis). Single crystal X-ray diffraction analysis revealed that dipicolinate ligand is coordinated to the chromium(III) ion in an O,N,O′-tridentate fashion, while its uncoordinated and coordinated carboxylate O atoms (with respect to Cr(III) ion) are in turn bound to potassium ions. Therefore, each dipicolinate ligand bridges two potassium ions and a chromium(III) ion between them, giving rise to a 2D coordination network. The coordination of chromium(III) ions is octahedral, while the coordination number of potassium ions is 8. The coordination networks are in turn assembled only by π–π stacking interactions into a 3D structure.Graphical Abstract2D mixed-metal coordination polymer, containing potassium, chromium(III) and dipicolinate ions, was prepared and characterized by spectroscopic methods (IR, Raman, UV/Vis) and its crystal structure was determined by single crystal X-ray structural analysis.

A new coordination mode of 6-methylnicotinic acid in trans-tetraaquabis(6-methylpyridine-3-carboxylato-kappaO)cobalt(II) tetrahydrate.

The title compound, [Co(C7H6NO2)2(H2O)4] x 4 H2O, contains a Co(II) ion lying on a crystallographic inversion centre. The Co(II) ion is octahedrally coordinated by two 6-methylpyridine-3-carboxylate ligands in axial positions [Co-O = 2.0621 (9) A] and by four water molecules in the equatorial plane [Co-O = 2.1169 (9) and 2.1223 (11) A]. There are also four uncoordinated water molecules. The 6-methylpyridine-3-carboxylate ligands are bound to the Co(II) ion in a monodentate manner through a carboxylate O atom. There is one strong intramolecular O-H...O hydrogen bond, and six strong intermolecular hydrogen bonds of type O-H...O and one of type O-H...N in the packing, resulting in a complex three-dimensional supramolecular structure.

A one-dimensional CdII coordination polymer: catena-poly[cadmium(II)-bis(mu-6-methylpicolinato)].

In the title compound, [Cd(C(7)H(6)NO(2))2]n, the Cd(II) ion has a distorted octahedral geometry. The 6-methylpyridine-2-carboxylate anions are perpendicular to one another and act as bidentate and bridging ligands. Two carboxylate O atoms bridge the Cd(II) ions, forming centrosymmetric dinuclear units. These units are further connected via carboxylate O atoms into a one-dimensional polymeric chain which extends in the [100] direction.

Building inorganic supramolecular architectures using principles adopted from the organic solid state

The possibility of converting crystal engineering principles that originate in the organic solid state into productive strategies for the effective supramolecular assembly of coordination complexes has been established through a range of complementary techniques. Calculated molecular electrostatic potentials, in conjunction with a systematic structural study, demonstrate that the existence and structural importance of the key hydrogen-bond interactions are not disrupted by the presence of metal cations and charge-balancing anions.

Two Different Barium(II) 2D Coordination Polymers Constructed with Pyrazine-2,3-Dicarboxylate: Synthesis, Crystal Structures, and Thermal Decomposition to Barium(II) Carbonate Nanoparticles

Two novel barium(ii) 2D coordination polymers, {[Ba(µ-H2O)(H2O)2(µ-pyzdc)]}n (1) and {[Ba(H2O)2(µ-Hpyzdc)(Hpyzdc)]2H2O}n (2) (pyzdcH2 = pyrazine-2,3-dicarboxylic acid), were prepared by reaction of barium(ii) chloride dihydrate and pyrazine-2,3-dicarboxylic acid under similar experimental conditions (slightly different pH values) and characterised by elemental analysis, IR spectroscopy, and thermogravimetric analysis/differential thermal analysis methods. Their crystal structures were determined by single-crystal X-ray structure analysis and it was revealed that the barium(ii) ion has a distorted bicapped square antiprismatic coordination geometry in 1 and a distorted tricapped trigonal prismatic geometry in 2, composed of water molecules, carboxylate O, and pyrazine N atoms in both cases. The polymers 1 and 2 have different connectivity, as the pyrazine-2,3-dicarboxylate ion acts as multidentate bridging ligand in both 1 and 2, but also as an N,O′-bidentate terminal ligand in 2. There are terminal coordinated water molecules in both 1 and 2, but bridging water molecules are present only in 1 and water molecules of crystallisation only in 2. BaCO3 nanoparticles were formed by thermal decomposition of 1 in the presence of polyethylene glycol, and their structure and morphology were studied by powder X-ray diffraction and scanning electron microscopy. According to the powder X-ray diffraction pattern, BaCO3 was formed with an orthorhombic witherite structure.

A Rare Example of a Dinuclear Cobalt(II) Complex with Dipicolinate and Bridging 2-Aminopyrazine Ligands. Preparation, Structural, Spectroscopic and Thermal Characterization

A dinuclear cobalt(II) complex, [Co2(H2O)4(dipic)2(μ-apyz)] (dipicH2 = pyridine-2,6-dicarboxylic (dipicolinic) acid, apyz = 2-aminopyrazine) (1), has been hydrothermally synthesized and characterized by elemental analyses, spectroscopic methods (IR, UV/Vis), thermal analysis as well as by X-ray diffraction studies. The dinuclear complex is composed of two cobalt(II) ions bridged by a 2-aminopyrazine molecule. Each cobalt(II) ion is coordinated by one nitrogen and two oxygen atoms of the tridentate dipicolinate anion, one heterocyclic nitrogen atom of the 2-aminopyrazine and two oxygen atoms of coordinated water molecules. The resulting geometry for the CoN2O4 coordination environment can be described as distorted octahedral. Various hydrogen bonds of the type O-H···O and N-H···O are also present in the crystal structure. This arrangement leads to the formation of a 3D structure. Graphical Abstract A Rare Example of a Dinuclear Cobalt(II) Complex with Dipicolinate and Bridging 2-Aminopyrazine Ligands. Preparation, Structural, Spectroscopic and Thermal Characterization

A Design of Mercury(II) Coordination Polymers with Pyridinedicarboxylic Acids: Structural, Spectroscopic and Thermal Studies

Two novel mercury(II) coordination polymers, two-dimensional [HgCl(2,3-pydcH)(H2O)]n (1) and one-dimensional [HgCl(2,5-pydcH)(DMF)]n (2) (2,3-pydcH2 = pyridine-2,3-dicarboxylic acid; 2,5-pydcH2 = pyridine-2,5-dicarboxylic acid), were prepared in the reactions of the corresponding pyridinedicarboxylic acid with mercury(II) chloride. Their structures were solved by the single-crystal X-ray diffraction method. Both 2,3-pydcH− and 2,5-pydcH− are partially deprotonated bridging ligands which display similar coordination modes, acting as N,O-bidentate and O’-monodentate ligands in the structures of 1 and 2, respectively. The presence of DMF in the reaction mixture led to the formation of a 1D coordination polymer, while a 2D coordination polymer was formed in the absence of DMF. Spectroscopic analysis of 1 and 2 was performed by IR spectroscopy in the solid state and by 1H and 13C NMR spectroscopy in the DMSO solutions. Thermal properties of the coordination polymers 1 and 2 were also investigated. NMR data support complete decomposition of 1 and a preserved polymeric structure of 2 in the DMSO solution.Graphical Abstract