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Two cadmium(II) coordination compounds [Cd(NCO) 2 (tppz)] ( 1 ) and [Cd 2 (μ 1,1 -NCO) 2 (μ 1,3 -NCO) 2 (μ-tppz)] n ( 2 ) have been successfully synthesized in the reaction of CdCl 2 or Cd(NO 3 ) 2 with a versatile polydentate ligand (2,3,5,6-tetrakis(2-pyridyl)pyrazine - tppz ) and pseudohalide NCO – ions. The resulted compounds were structurally characterized by single crystal X-ray diffraction analysis and further characterized by infrared spectra, powder X-ray diffraction and thermal analysis. The photoluminescence behaviour was investigated in solid state for 1 and 2 and then compared to the free organic ligand. The luminescent properties of tppz were investigated for two polymorphs (monoclinic P2 1 / n and tetragonal I4 1 / a ). Moreover, the Hirshfeld surface analysis has been used to determine the effect of intermolecular interactions on emission properties of these polymorphs. In addition, the luminescent properties of mononuclear coordination compound were examined in acetonitrile solution.

Three new thiocyanate coordination compounds [Cd(NCS)2(μ-tppz)]n (1), [Cd(NCS)(NO3)(tppz)(H2O)] (2), [Cd2(μ1,3-NCS)2(NO3)2(μ-tppz)]n (3) have been successfully synthesized in the reaction of Cd(NO3)2·4H2O or CdCl2·2.5H2O with a versatile polydentate ligand (2,3,5,6-tetrakis(2-pyridyl)pyrazine – tppz) and NCS− anion. The resulted compounds were structurally characterized by single crystal X-ray diffraction analysis and further characterized by infrared spectra, powder X-ray diffraction and thermal analysis. The studies demonstrated a significant impact of the reaction conditions and cadmium salt on the final molecular structures. The compounds 1 and 3 displays an infinitive one-dimensional chain made up of cadmium(II) ions linked by only through tppz bridges (in 1) or a single thiocyanate bridges μ1,3-NCS− and tppz molecules (in 3). The structure 2 consist of the mononuclear, heptacoordinated molecules [Cd(NCS)(NO3)(tppz)(H2O)] assembled by π⋯π and C–S⋯π type interactions into three dimensional supramolecular network. The photoluminescence behavior of 1–3 was investigated in solid state. In addition, the luminescent properties of the mononuclear coordination compound (2) were examined in acetonitrile solution.

Five oxalato-bridged heterobimetallic compounds of general formula [ReCl4(ox)M(bdmpzm)2].2MeCN [ox = oxalate, bdmpzm = bis(3,5-dimethylpyrazol-1-yl)methane and M = Zn (1),Cu (2), Ni (3), Co (4) and Mn (5)] have been successfully synthesized in self-assembly reactions of the [ReCl4(ox)]2- metalloligand with the coordinatively unsaturated [M(bdmpzm)2]2+ complex generated in situ by the reaction of the suitable metal(II) salt with the bdmpzm ligand. 1-5 are isostructural compounds whose crystal structures consist of neutral heterodinuclear [ReCl4(ox)M(bdmpzm)2] units and free acetonitrile molecules. The magnetic properties of 1-5 were investigated in the temperature range 2.0-300 K. The nature and trend of the magnetic interactions in 2-4 is discussed in the light of the number and symmetry of the magnetic orbitals involved and compared with those reported in previous magneto-structural studies where the [ReCl4(ox)]2- was used as a metalloligand towards first-row transition metal ions.

The reaction of the starting materials [ReIIICl3(MeCN)(PPh3)2] or [ReVOCl3(PPh3)2] with 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) in acetonitrile yielded the Re(III) complex [ReCl3(tppz)]·MeCN (1). This complex crystallizes in the monoclinic space group P21/n and its crystal structure consists of neutral mononuclear entities with meridional geometry of the chloride ligands, and the six-coordination of the Re(III) ion being completed by the tridentate tppz ligand. Each metal centre exhibits a highly distorted octahedral coordination with Re–Cl and Re–Ntppz bond lengths covering the ranges 2.3590(9)–2.3606(8) and 1.971(2)–2.096(2) A, respectively. The magnetic properties of 1 have been investigated in the temperature range 1.9–290 K. They are characteristic of a six-coordinate Re(III) mononuclear complex with d4 low-spin (3T1 ground state). The magnetic data of 1 are discussed through a deep analysis of the influence of the ligand-field, spin–orbit coupling, tetragonal distortion and covalency effects. The second-order Zeeman effect between the non-magnetic ground state (MJ = 0) and higher energy levels (MJ ≠ 0) determines the magnetic susceptibility of 1, the value of the temperature-independent paramagnetic susceptibility being 3378 × 10−6 cm3 mol−1. This value compares well with those reported for other structurally characterized Re(III) complexes.

The acetonitrile solution of NH 4 ReO 4 added to methanol/acetonitrile solution of Cu(NO 3 ) 2 with bis(pyrazol-1-yl)methane leads to the blue heterobimetallic [Cu(bpzm) 2 ][ReO 4 ] 2 ( 1 ) complex in which perrhenate is linked via oxygen with copper(II) ion. The reaction with bis(3,5-dimethylpyrazol-1-yl)methane under the same conditions gave [Cu(bdmpzm) 2 ][NO 3 ]·[ReO 4 ]·CH 3 CN ( 2 ) complex in which perrhenate exists as counterion. Both complexes were structurally characterized and in solid state by IR, UV–Vis–NIR spectroscopy and magnetic susceptibility measurements. The magnetic data indicated paramagnetism of both complexes with the weak magnetic short-range interactions and without frustration of the spins below 2 K.

The imido rhenium(V) complexes [Re(p-NC6H4CH3)X(OMe)(Hdpa)(PPh3)]ReO4 (Hdpa = 2,2′-dipyridylamine and X = Cl in 1 and Br in 2) have been synthesized and characterised spectroscopically and structurally (by single-crystal X-ray diffraction). The experimental studies on 1 have been accompanied computationally by the density functional theory (DFT) and time-dependent DFT calculations. Additional information about the Re–NR bond characteristics in [Re(p-NC6H4CH3)Cl(OMe)(Hdpa)(PPh3)]+ was obtained by NBO analysis.

The p-tolyldiazenido ruthenium(II) complexes [RuCl3(PPh3)2(N2PhCH3)]� CH3OH (1), [RuCl3(PPh3) (N2PhCH3)(HPz)] (2) and [RuCl3(PPh3)(N2PhCH3)(Im)]� CH3OH (3) were synthesized and characterized by IR, 1 H, 13 C, 31 P NMR, electronic absorption and emission spectroscopy, and X-ray crystallography. In the molecular structure of complex (1) some p–p stacking interactions are observed, whereas in the structure of the imidazole complex (3) graph set analysis shows intermolecular hydrogen bonded rings. The electronic structures of the complexes were calculated by DFT based on their crystal structures. The spin-allowed singlet–singlet electronic transitions of the complexes were calculated by time-dependent DFT and the UV–Vis spectra have been discussed on this basis. The emission properties of the complexes were also studied.

The paper presents a combined experimental and computational study of novel oxorhenium(V) complexes of benzothiazole (bt) and 2-(2-aminophenyl)benzothiazole (apbt). The complexes [Re2O3Cl4(bt)4]·H2O (1·H2O), [ReO(OEt)Cl2(bt)(PPh3)]·Me2CO (2·Me2CO), [ReO(OPri)Cl2(bt)(PPh3)] (3), [ReOCl2(apbt)(OPPh3)] (4) and [ReOCl2(apbt)(OAsPh3)]·0.5CHCl3 (5·0.5CHCl3) have been characterized structurally (by single-crystal X-ray diffraction) and spectroscopically (by IR, NMR, UV–Vis). For compounds 1, 2 and 4, DFT and TD-DFT calculations have been performed to obtain their IR and UV–Vis absorption spectra, and satisfactory theoretical–experimental agreement was achieved. Additional information about binding between the rhenium atom and oxo ligand in the complexes 1, 2 and 4 has been obtained by NBO analysis.

Three novel imido rhenium complexes of biologically relevant ligand 2-hydroxymethylbenzimidazole: [Re(p-NC6H4CH3)Cl2(hmbzim)(PPh3)]·CHCl3 (1), [Re(p-NC6H4CH3)Br2(hmbzim)(PPh3)] (2) and [Re(p-NC6H4CH3)(hmbzim)2(PPh3)]ReO4·MeOH (3) have been synthesized and characterized spectroscopically and structurally (by single-crystal X-ray diffraction). The electronic spectra of 1 and 3 were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. Additional information about binding in the complexes 1 and 3 was obtained by NBO analysis, which confirms a linear coordination mode of the p-NC6H4CH3 ligand and triple bond between the rhenium and imido ligand.

Novel p-tolylimido rhenium(V) complexes trans -[Re(p-NC 6 H 4 CH 3 )X 2 (quin-2-COO)(PPh 3 )] and cis -[Re(p-NC 6 H 4 CH 3 )X 2 (quin-2-COO)(PPh 3 )]·MeCN have been obtained in the reactions of [Re(p-NC 6 H 4 CH 3 )X 3 (PPh 3 ) 2 ] (X = Cl, Br) with quinoline-2-carboxylic acid. The compounds were identified by elemental analysis IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structures of trans - and cis -halide isomers of [Re(p-NC 6 H 4 CH 3 )Cl 2 (quin-2-COO)(PPh 3 )] have been calculated with the density functional theory (DFT) method. Additional information about binding in the compounds [Re(p-NC 6 H 4 CH 3 )Cl 2 (quin-2-COO)(PPh 3 )] with cis- and trans -halide arrangement has been obtained by NBO analysis. The electronic spectra of trans and cis isomers of [Re(p-NC 6 H 4 CH 3 )Cl 2 (quin-2-COO)(PPh 3 )] were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.

Novel rhenium(V) oxocomplexes have been obtained in the reactions of [ReOX3(EPh3)2] (X = Cl, Br; E = P, As) with 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (HL). All the compounds were identified by elemental analysis IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure and spectroscopic features of [ReOBr2(L)(PPh3)] have been further investigated by means of the density functional theory (DFT) and time-dependent DFT methods. Additional information about binding in the title compounds has been obtained by NBO analysis.

The reaction of [ReO(OMe)Cl2(dpphen)] (dpphen = 4,7-diphenyl-1,10-phenanthroline) with triphenylphosphine has been examined and two novel rhenium complexes – [ReIIICl3(dpphen)(PPh3)]·Me2CO (1) and [ReIVCl4(dpphen)]·CHCl3 (2) – have been obtained. The compounds have been characterised by elemental analysis, IR, UV–Vis spectroscopy, magnetic measurements and X-ray crystallography. The electronic structures of [ReCl3(dpphen)(PPh3)] and [ReCl4(dpphen)] have been studied by DFT/B3LYP level calculations, and TD-DFT calculations have been employed for discussion of the electronic spectra in more detail. The magnetic behaviour of 1 is characteristic of mononuclear complexes with d4 low-spin octahedral Re(III) complexes (3T1g ground state) and arise because of the large spin–orbit coupling (ζ = 2500 cm−1), which gives diamagnetic ground state. For complex 2 the results of calculations revealed value of zero-field splitting parameter D = 10.8 cm−1, g|| = 2.49 and g⊥ = 1.51.

Novel p-tolylimido rhenium(V) complexes [Re(p-NC6H4CH3)X2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]X (X = Cl, Br) have been obtained in the reactions of [Re(p-NC6H4CH3)X3(PPh3)2] with 2-(2-hydroxyphenyl)-1H-benzimidazole (Hhpb). The compounds were identified by elemental analysis IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structures of the complex [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and the cation [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ have been calculated with the density functional theory (DFT) method. Additional information about binding in the [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ has been obtained by NBO analysis. The electronic spectra of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]Cl were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.

A novel rhenium complex of multi-dentate ligand 2,3,5,6-tetra(2-pyridyl)pyrazine – [ReCl(tppz)(PPh3)2][ReO4] – has been synthesized and characterised spectroscopically and structurally. The electronic spectrum of [ReCl(tppz)(PPh3)2][ReO4] has been investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.

The p-tolylimido rhenium(V) complexes [Re(p-NC6H4CH3)X3(EPh3)2] (X = Cl, Br; E = As, P) and [Re(p-NC6H4CH3)Cl2(hmpbta)(PPh3)]·MeCN have been synthesized and characterized spectroscopically and structurally. The electronic spectra of [Re(p-NC6H4CH3)Cl3(PPh3)2] and [Re(p-NC6H4CH3)Cl2(hmpbta)(PPh3)](Hhmpbta-2-(2′-hydroxy-5′-methylphenyl)benzotriazole) were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. Additional information about bonding between the rhenium atom and p-tolylimido ligand in the complexes [Re(p-NC6H4CH3)Cl3(PPh3)2] and [Re(p-NC6H4CH3)Cl2(hmpbta)(PPh3)] was obtained by NBO analysis.

Two new Re(iv) compounds of formulae H2tppz[ReCl6] (1) and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(iv) anions and diprotonated H2tppz(2+) cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)2](2+) and [(ox)ReCl3(μ-Cl)Cu(2)(bpzm)2(μ-Cl)ReCl3(ox)](2-) entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9-295 K. 1 is a magnetically diluted Re(iv) complex, the relatively large value of the zero-field splitting of the ground level [D = -15.8(2) cm(-1)] accounting for the variation of χMT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(iv) and Cu(ii) through oxalate (J1 = +0.15 cm(-1)) and single chloro (J2 = +4.9 cm(-1)) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(iv) ion (DRe = 42 cm(-1)). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (Hc) being 20 kOe.