Synthesis and Reactivity of Phenylimidorhenium(V) Complexes with N‐[(N′,N′‐Dialkylamino)(thiocarbonyl)]benzamidines. Observation of a pH‐Dependent Isomerisation of Related Oxorhenium(V) Compounds

Reactions of [Re(NPh)Cl₃(PPh₃)₂] with N‐[(N′,N′‐dialkylamino)(thiocarbonyl)]benzamidines (H₂R₂tcb) (R₂ = Et₂, (CH₂)₂O(CH₂)₂) in methanol give mono‐chelates of the composition [Re(NPh)Cl₂(PPh₃)(HR₂tcb)] as the sole products independent of the amount of the added H₂R₂tcb. Addition of a supporting base such as NEt₃ results in hydrolysis of the Re=NPh bonds and partial hydrolysis of the thiocarbamoylbenzamidines. Orange‐brown, cationic oxorhenium(V) compounds of the formula [ReO(HR₂tcb)₂]Cl were isolated from such reaction mixtures in good yields, and the formation of small amount of the unusual sulfido/persulfido‐bridged Re^V dimer [{ReO(HEt₂tcb)}₂(μ‐S)(μ‐S₂)] give evidence for a considerable degree of ligand decomposition under such conditions. The products have been characterized by spectroscopic methods and X‐ray crystallography. Acidification of orange‐brown solutions of the five‐coordinate Re^V oxo complex [ReO(HEt₂tcb)₂]Cl causes an immediate change of the color and deep blue crystals of the neutral, six‐coordinate [ReOCl(HEt₂tcb)₂] can be isolated from the resulting mixture. Alternatively, the product can be prepared by a ligand‐exchange protocol starting from (NBu₄)[ReOCl₄] and H₂Et₂tcb. The pH‐dependent isomerization between [ReO(HEt₂tcb)₂]Cl and [ReOCl(HEt₂tcb)₂] is reversible.     

Phenylimido Complexes of Technetium and Rhenium with Maleonitriledithiolate

[Tc(NPh)Cl₃(PPh₃)₂] or [Re(NPh)Cl₃(PPh₃)₂] react with two equivalents of Na₂mnt (mnt^2– = 1,2‐dicyanoethene‐1,2‐dithiolate) with formation of anionic complexes of the composition [M(NPh)(mnt)₂]^–. The products can be isolated as large red blocks of their AsPh₄⁺ salts. The complex anions contain square‐pyramidal coordinated metal atoms with the phenylimido ligands in apical positions. The M–N–C bonds are almost linear. A similar phenylimido complex with an additional amino group was synthesized from [Re(NC₆H₄‐4‐NH₂)Cl₃(PPh₃)₂]. The presence of such substituents may allow coupling of the metal complexes to biomolecules such as peptides, proteins, or sugars, provided the M=N bonds are sufficiently stable against hydrolysis.     

Syntheses and Structures of Nitridorhenium(V) and Nitridotechnetium(V) Complexes with N,N‐[(Dialkylamino)(thiocarbonyl)]‐N′‐(2‐hydroxyphenyl)benzamidines

[MNCl₂(PPh₃)₂] complexes (M = Re, Tc) react with N‐[(dialkylamino)(thiocarbonyl)]‐N′‐(2‐hydroxyphenyl)benzamidines (H₂L¹) with formation of neutral, five‐coordinate nitrido complexes of the composition [MN(L¹)(PPh₃)]. The products have distorted square‐pyramidal coordination spheres with each a tridentate, double‐deprotonated benzamidine and a PPh₃ ligand in their basal planes.     

Nitridorhenium(V) Complexes with 1,3‐Dialkyl‐4,5‐dimethylimidazole‐2‐ylidenes

The nitridorhenium(V) complexes [ReNCl₂(PR₂Ph)₃] (R = Me, Et) react with the N‐heterocyclic carbenes (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐5‐ylidene (L^Et) or 1,3,4,5‐tetramethylimidazole‐2‐ylidene (L^Me) in absolutely dry THF under complete replacement of the equatorial coordination sphere. The resulting [ReNCl(L^R)₄]⁺ complexes (L^R = L^Me, L^Et) are moderately stable as solids and in solution, but decompose in hot methanol under formation of [ReO₂(L^R)₄]⁺ complexes. With 1,3‐diisopropyl‐4,5‐dimethylimidazole‐5‐ylidene (L^i‐Pr), the loss of the nitrido ligand and the formation of a dioxo species is more rapid and no nitridorhenium intermediate could be isolated. The Re‐C bond lengths in [ReNCl(L^Et)₄]Cl of approximately 2.195Å are relatively long and indicate mainly σ‐bonding in the electron‐deficient d² system under study. The hydrolysis of the nitrido complexes proceeds via the formation of [ReO₃N]^2? anions as could be verified by the isolation and structural characterization of the intermediates [{ReN(PMe₂Ph)₃}{ReO₃N}]₂ and [{ReN(OH₂)(L^Et)₂}₂O][ReO₃N].     

Oxorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

Reactions of the oxorhenium(V) complexes [ReOX₃(PPh₃)₂] (X = Cl, Br) with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (L^Ph) under mild conditions and in the presence of MeOH or water give [ReOX₂(Y)(PPh₃)(L^Ph)] complexes (X = Cl, Br; Y = OMe, OH). Attempted reactions of the carbene precursor 5‐methoxy‐1,3,4‐triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazole ( 1 ) with [ReOCl₃(PPh₃)₂] or [NBu₄][ReOCl₄] in boiling xylene resulted in protonation of the intermediately formed carbene and decomposition products such as [HL^Ph][ReOCl₄(OPPh₃)], [HL^Ph][ReOCl₄(OH₂)] or [HL^Ph][ReO₄] were isolated. The neutral [ReOX₂(Y)(PPh₃)(HL^Ph)] complexes are purple, airstable solids. The bulky NHC ligands coordinate monodentate and in cis‐position to PPh₃. The relatively long Re–C bond lengths of approximate 2.1Å indicate metal‐carbon single bonds.     

Oxorhenium(V)‐ and Tricarbonylrhenium(I) Complexes with Substituted Pyrazoles as Products of the Degradation of Hydrotrispyrazolylborates

Hydrotris(3, 5‐dimethylpyrazol‐1‐yl)borate and hydrotris(3‐phenylpyrazol‐1‐yl)borate decompose during reactions with [ReOCl₃(PPh₃)₂] and [NEt₄]₂[Re(CO)₃Br₃], respectively. The generated pyrazole ligands form complexes with the rhenium(V) oxo and the rhenium(I ) tricarbonyl cores. X‐ray crystal structures of the oxo‐bridged dimer [Cl(PPh₃)(O)Re(μ‐O)(μ‐Me₂pz)₂Re(O)(HMe₂pz)Cl] ( 1 ) and [Re(CO)₃(HPhpz)₂(Phpz)] ( 2 ) (HMe₂pz = 3, 5‐dimethylpyrazole, HPhpz = 3‐phenylpyrazole) show that the substituted pyrazoles can readily deprotonate and act as monodentate or bridging anionic ligands. Re‐N bond lengths between 2.09 and 2.14Å have been observed for the bridging and between 2.12 and 2.23Å for the terminal pyrazole ligands.     

Phenylimidorhenium(V) Complexes with 1,3‐Diethyl‐4,5‐dimethylimidazole‐2‐ ylidene Ligands

The phenylimidorhenium(V) complexes [Re(NPh)X₃(PPh₃)₂] (X = Cl, Br) react with the N‐heterocyclic carbene (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐2‐ylidene (L^Et) under formation of the stable rhenium(V) complex cations [Re(NPh)X(L^Et)₄]²⁺ (X = Cl, Br), which can be isolated as their chloride or [PF₆]^? salts. The compounds are remarkably stable against air, moisture and ligand exchange. The hydroxo species [Re(NPh)(OH)(L^Et)₄]²⁺ is formed when moist solvents are used during the synthesis. The rhenium atoms in all three complexes are coordinated in a distorted octahedral fashion with the four NHC ligands in equatorial planes of the molecules. The Re–C(carbene) bond lengths between 2.171(8) and 2.221(3) Å indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atoms. Attempts to prepare analogous phenylimido complexes from [Re(NPh)Cl₃(PPh₃)₂] and 1,3‐diisopropyl‐4,5‐dimethylimidazole‐2‐ylidene (L^i?Pr) led to a cleavage of the rhenium‐nitrogen multiple bond and the formation of the dioxo complex [ReO₂(L^i?Pr)₄]⁺.     

Oxorhenium(V) Complexes with Thiosemicarbazones

Neutral oxorhenium(V) complexes with thiosemicarbazones derived from 2‐pyridine formamide, HL¹, are formed when [ReOCl₃(PPh₃)₂] reacts with equimolar amounts of the ligands. Reduction of the metal and the formation of rhenium(III) complexes of the composition [Re(L¹)₂]⁺ occurs when an excess of thiosemicarbazones is used and the reaction is performed in boiling toluene for a prolonged period of time. The thiosemicarbazones deprotonate and act as tridentate ligands as has been confirmed by an X‐ray structure of [ReOCl₂(L^1b)], where HL^1b is 2‐pyridineformamide‐N(4)‐ethylthiosemicarbazone and the ligand occupies the equatorial coordination sphere of the complex together with one of the chloro ligands.     

Rhenium(V) Complexes with Bidentate N,O-Donor Imidazole Derivatives

The reaction of a two-fold molar excess of the potential N,O-donor ligand 2-(hydroxymethyl)-1-methylimidazole (Hmi) with trans-[ReOCl₃(PPh₃)₂] led to the isolation of cis-[ReOCl₂(mi)(PPh₃)]. An X-ray structure determination indicated that the complex has distorted octahedral geometry, and that mi coordinates as a bidentate with the alcoholate oxygen trans to the oxo group. A similar reaction with 2-(1-ethyloxomethyl)-1-methylimidazole (eomi), the ethyl substituted analogue of Hmi, led to the formation of the oxo-bridged dinuclear complex [(μ-O){ReOCl₂(eomi)₂}₂]. The ligand eomi coordinates as a monodentate via the imidazole nitrogen, with the "hard" ether oxygen uncoordinated. An X-ray crystal structure indicates that the chlorides are trans to each other in the ReN₂Cl₂ planes, which are orthogonal to the O=Re-O-Re=O backbone.     

Oxidorhenium(V) and Rhenium(III) Complexes with m-Terphenyl Isocyanides

Reactions of the sterically encumbered m-terphenyl isocyanides CNAr^Dipp2 (Dipp = 2,6-diisopropylphenyl) and CNAr^Mes2 (Mes = 2,4,6-trimethylphenyl) with (NBu₄)[ReOCl₄] in CH₂Cl₂ form stable complexes of the composition (NBu₄)[ReOCl₃(CNAr^R)] or [ReOCl₃(CNAr^R)₂] depending on the amount of isocyanide added. In the [ReOCl₃(CNAr^R)₂] complexes, cis coordination of the two isocyanides is observed for CNAr^Mes2, while the sterically more demanding CNAr^DIPP2 ligands are found in trans positions. The rhenium(III) species [ReCl₃(PPh₃)(CNAr^Mes2)₂] was obtained from the reaction of [ReOCl₃(PPh₃)₂] and CNAr^Mes2. The ν(CN) IR frequencies measured for the Re^V complexes appear at higher wavenumbers than for the uncoordinated isocyanides, which suggests a low degree of backdonation into anti-bonding orbitals of these ligands.     

New Rhenium(V) Nitrofuryl Semicarbazone Complexes.Crystal Structure of [ReOCl2(PPh3)(3‐(5‐Nitrofuryl)acroleine semicarbazone)]

The synthesis and characterization of the first two Re complexes with semicarbazone ligands is presented. Selected ligands are 5‐Nitro‐2‐furaldehyde semicarbazone (Nitrofurazone) ( L1 ) and its derivative 3‐(5‐Nitrofuryl)acroleine semicarbazone ( L2 ). Complexes of general formula [Re^VOCl₂(PPh₃) L ], where L = L1 and L2 , were prepared in good yields and high purity by reaction of [Re^VOCl₃(PPh₃)₂] with L in ethanol or methanol solutions. The complexes formula and molecular structures were supported by elemental analyses and electronic, FTIR, ¹H, ¹³C and ³¹P NMR spectroscopies. In addition, the crystal and molecular structure of [Re^VOCl₂(PPh₃) L2 ] was determined by X‐ray diffraction methods. [ReOCl₂(PPh₃)(3‐(5‐Nitrofuryl)acroleine semicarbazone)] crystallizes in the space group P‐1 with a = 11.2334(2), b = 11.3040(2), c = 12.5040(2) Å, α = 81.861(1), β = 63.555(1), γ = 83.626(1)°, and Z = 2. The Re(V) ion is in a distorted octahedral environment, equatorially coordinated to a deprotonated semicarbazone molecule acting as a bidentate ligand through its carbonylic oxygen and azomethynic nitrogen atoms, to an oxo ligand and a chlorine atom. The six‐fold coordination is completed by another chlorine atom and a triphenylphosphine ligand at the axial positions.     

Nitridorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

[ReNCl₂(PPh₃)₂] and [ReNCl₂(PMe₂Ph)₃] react with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (HL^Ph) under formation of the stable rhenium(V) nitrido complex [ReNCl(HL^Ph)(L^Ph)], which contains one of the two NHC ligands with an additional orthometallation. The rhenium atom in the product is five‐coordinate with a distorted square‐pyramidal coordination sphere. The position trans to the nitrido ligand is blocked by one phenyl ring of the monodentate HL^Ph ligand. The Re–C(carbene) bond lengths of 2.072(6) and 2.074(6) Å are comparably long and indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atom. The chloro ligand in [ReNCl(HL^Ph)(L^Ph)] is labile and can be replaced by ligands such as pseudohalides or monoanionic thiolates such as diphenyldithiophosphinate (Ph₂PS₂^?) or pyridine‐2‐thiolate (pyS^?). X‐ray structure analyses of [ReN(CN)(HL^Ph)(L^Ph)] and [ReN(pyS)(HL^Ph)(L^Ph)] show that the bonding situation of the NHC ligands (Re–C(carbene) distances between 2.086(3) and 2.130(3) Å) in the product is not significantly influenced by the ligand exchange. The potentially bidentate pyS^? ligand is solely coordinated via its thiolato functionality. Hydrogen atoms of each one of the phenyl rings come close to the unoccupied sixth coordination positions of the rhenium atoms in the solid state structures of all complexes. Re–H distances between 2.620 and 2.712Å do not allow to discuss bonding, but with respect to the strong trans labilising influence of “N^3?”, weak interactions are indicated.     

Syntheses,Spectra, Thermal Studies and Crystal Structures of Vitamin B13 Complexes of Nickel(II) with N,N,N′,N′‐Tetramethylethylenediamine and 2,2‐Dimethylpropane‐1,3‐diamine

Two nickel(II) complexes of vitamin B13 (H₃Or) with N,N,N′,N′‐tetramethylethylenediamine (tmen) and 2,2‐dimethylpropane‐1,3‐diamine (dmpen) were synthesized and characterized by means of elemental and thermal analyses, magnetic susceptibility, and IR and UV/Vis spectroscopic studies. The crystal structures of mer‐[Ni(HOr)(H₂O)₂(tmen)] · H₂O ( 1 ) and [Ni(HOr)(dmpen)₂] ( 2 ) were determined by using single‐crystal X‐ray diffraction. In the complexes, which crystallize in the triclinic system (space group for 1 ) and the monoclinic system (space group P2₁/c for 2 ), the Ni^II ions exhibit a distorted octahedral coordination. Ni^II ions are chelated by the deprotonated nitrogen atom of the pyrimidine ring and the oxygen atom of the carboxylate group, the distorted octahedral coordination completed by one tmen and two aqua ligands for 1 or two dmpen ligands for 2 .     

Dimeric Rhenium(I) Carbonyl Complexes with Thiosemicarbazone Backbone

Dimeric, neutral rhenium(I) complexes of the composition [Re₂(CO)₆X(L^R)] (X = Cl or Br) are formed when [NEt₄]₂[Re(CO)₃Br₃] or [Re(CO)₃Cl(CH₃CN)₂] react with 2, 2′-dipyridylketone thiosemicarbazones (HL^R, R = H, Ph). The thiosemicarbazones deprotonate during the reaction and connect two tricarbonylrhenium(I) units as formally pentadentate bridging ligands. This results in an extremely rare coordination mode, in which the two nitrogen atoms of the hydrazone unit bind to each one of the rhenium atoms. The bond lengths inside the thiosemicarbazonato backbone reflect a large degree of delocalization of electron density.     

Rhenium(I) and Technetium(I) Tricarbonyl Complexes with Phosphoraneimines

[NEt₄]₂[Re(CO)₃Br₃] and [NEt₄]₂[Tc(CO)₃Cl₃] react with trimethylsilyltriphenylphosphoraneimine, Me₃SiNPPh₃, under exchange of the bromo ligands and the formation of cationic [M(CO)₃(HNPPh₃)₃]⁺ complexes (M = Re, Tc). The required protons are abstracted from the solvent CH₂Cl₂. The steric bulk of the organic ligands causes a marked distortion of the established coordination polyhedra from an idealized octahedron with bond angles between neighbouring donor atoms between 81.81(8)° and 96.66(8)°. The reaction of [NEt₄]₂[Re(CO)₃Br₃] with Me₃SiNP(Ph₂)CH₂PPh₂ in CH₂Cl₂ yields the neutral complex [Re(CO)₃Br{HNP(Ph₂)CH₂PPh₂)], which contains a neutral, chelate‐bonded (diphenylphosphinomethyl)diphenylphosphoraneimine ligand. A similar reaction with the bifunctional phosphoraneimine Me₃SiNP(Ph₂)CH₂(Ph₂)PNSiMe₃ gives only small amounts of a binuclear rhenium(I) complex of the composition [{Re(CO)₃Br₂}₂(HNP(Ph₂)CH₂(Ph₂)PNH)]^2‐, whereas the major amount of the bis‐phosphoraneimine undergoes an intramolecular rearrangement to yield [H₂NP(Ph₂)NP(Ph₂)CH₃]Br. An X‐ray structure analysis shows a widespread delocalization of electron density over the central part of the cation.     

Synthese,Komplexbildung und Kristallstrukturen von Cyclotriphosphazenen mit N,N,N′,N′‐Tetramethylguanidingruppen

Synthesis, Complex Formation, and Crystal Structures of Cyclotriphosphazenes with N,N,N′,N′‐Tetramethylguanidine Groups The reactions of monochloropentaphenoxycyclotriphosphazene and hexachlorocyclotriphosphazene with N,N,N′,N′‐tetramethylguanidine yield the mono and tetra substituted products 2‐(N,N,N′,N′‐tetramethylguanidine)‐2,4,4,6,6‐pentaphenoxy‐2 λ⁵,4 λ⁵,6 λ⁵‐cyclotriphosphaza‐1,3,5‐trien ( 1 ) and 2,2‐dichlor‐4,4,6,6‐tetra‐(N,N,N′,N′‐tetramethylguanidine‐2 λ⁵,4 λ⁵,6 λ⁵‐cyclotriphosphaza‐1,3,5‐trien ( 2 ) respectively; no hexa functionalized product could be obtained, even with high excess of the nucleophile. Electron release from the exocyclic amino substituent reduces the acceptor ability of the phosphorus atoms. Reactions of ( 2 ) with copper(II) chloride and palladium(II) bis(acetonitrilo)dichloride yield metal complexes with a ligand : metal ratio of 1 : 2. The X‐ray structure analyses of N₃P₃Cl₂(NC(N(CH₃)₂)₂)₄ · 2 CuCl₂ ( 2 a ) and N₃P₃Cl₂(NC(N(CH₃)₂)₂)₄ · 2 PdCl₂ ( 2 b ) show that each metal atom is coordinated by two imino nitrogen atoms in geminal positions and two chloride atoms in a square planar arrangement.     

Rhenium(V) Complexes of N,N′-Ethylenebis(2-mercaptopropanamide). Synthesis,Characterization, and X-ray Crystal Structures

The preparation of benzoyl-protectcd N,N′-ethylenebis(2-mercaptopropanamide) (H₄emp) and its ligand-exchange reaction with ReO₂(en)₂Cl are described. Three diastereomers, [syn-ReO(meso-emp)]; [anti-ReO(meso-emp)]-, and a pair of cnantiomers, [ReO(rac-emp)]-, were formed due to syn and anti orientation of the two methyl groups of the ligand relative to the ReO core. The diastereomers were separated by reverse phase C₁₈ semipreparative HPLC and isolated as salts of [Ph₄As][ReO-(emp)]. The structures of [Ph₄ As][ReO(meso-emp)] were determined by single-crystal X-ray analyses. [Ph₄As][syn-ReO(mesocmp)]H₂O crystallizes in triclinic space group Pl with a = 10.326(3) Å, b = 13.672(4) A, c = 14.023(5) Å, α = 61.20(2)°, β =74.74(3)°, γ= 75.68(2)° V = 1656.6(8) ų, Z = 2, Dc = 1.676 gmL^?1, F(000) = 824 and R = 0.0329 for 5877 unique reflections. For (he complex [Ph₄As][anti-ReO(meso-emp)], the crystal data are: monoclinic, space group P2₁/n, a = 9.128(2) Å, b = 24.284(7) Å, c = 14.112(4) Å, β = 93.41(2)° V = 3122.5(15) À³, Z = 4, Dc = 1.740 gmL^?1, F(000) = 1608 and R = 0.0361 for 5487 unique reflections. In both structures the rhenium atom is penta-coordinated and in an approximately square pyramidal environment.     

Spectrophotometric Determination of Rhenium(IV) with Thiocyanate,TX-100 and N,N′-Diphenylbenzamidine

A spectrophotometric method to determine rhenium(IV) at trace level is based on the extraction of Re(IV)-SCN^? complex in sulphuric acid media with N,N′-diphenylbenzamidine(DPBA) in presence of a non-ionic surfactant triton X-100 (TX-100) in chloroform. The complex shows maximum absorbance at 435 nm with amolar absorptivity value of 4.24 × 10⁴ L mol^?1 cm^?1 at an acidity range 3.5-6.5 M H₂SO₄. The method followed Beer's Law for the system Re(IV)-SCN^?(TX-100)-DPBA upto 4.0 μg Re(IV) mL^?1. The detection limit of the method is 5 ppb. None of the tested foreign ions, except molybdenum(VI), interfere with the determination of rhenium. The interference due to molybdenum could effectively be removed by prior precipitation with oxine. The effect of various analytical parameters on the extraction of the metal are discussed.     

(PPh4)2[Cl2Re(N3S2)(μ‐NSN)(μ‐N≡ReCl3)]2 – ein Rhenium(VII)‐Komplex mit einer Nitrido‐, einer Dinitridosulfato(II)‐ und einer Rhena‐3,5‐dithia‐2,4,6‐triazino‐Funktion

(PPh₄)₂[Cl₂Re(N₃S₂)(μ‐NSN)(μ‐N≡ReCl₃)]₂ – a Rhenium(VII) Complex with a Nitrido, a Dinitridosulfato(II), and a Rhena‐3,5‐dithia‐2,4,6‐triazino Function The title compound has been prepared from PPh₄[Re^VIICl₄(NSCl)₂] with N(SiMe₃)₃ in dichloromethane solution to give red‐brown single crystals, which were suitable for a crystal structure determination. As a by‐product PPh₄[ReNCl₄] is formed. (PPh₄)₂[Cl₂Re^VII(N₃S₂)(μ‐NSN)(μ‐N≡Re^VIICl₃)]₂ ( 1 ): Space group P2₁/c, Z = 2, lattice dimensions at –80 °C: a = 1280.8(2), b = 1017.5(1), c = 2467.8(3) pm, β = 95.04(1)°, R = 0.049. The complex anion of 1 consists of a planar ReN₃S₂‐heterocycle which is connected with the second rhenium atom by a μ‐nitrido bridge as well as by a μ‐dinitridosulfato(II) ligand to form a planar Re₂(N)(NSN) six‐membered heterocycle. This [Cl₂Re(N₃S₂)(μ‐NSN)(μ‐N≡ReCl₃)]^– unit dimerizes via one of the N‐atoms of the (NSN)^4– ligand to give a centrosymmetric Re₂N₂ four‐membered ring.     

Complexes of diorganotin(IV) dihalides with N,N′-dimethyl-2, 2′-bisimidazole

Adducts of N, N′ -dimethyl-2, 2′-bisimidazole (DMBIm) with diethyl- and dibutyl-tin(IV) dihalides (Cl, Br) have been isolated and characterized. IR data for [SnR₂X₂(DMBIm)] compounds are in keeping with a six-coordinate tin atom with DMBIm acting as a bidentate ligand, whereas in [(SnR₂X₂)₂(DMBIm)] the tin is five-coordinate and DMBIm acts as a bridging ligand. Measurements of conductivity in acetonitrile show the adducts to behave as non-ionogens in this solvent. NMR data show them to undergo dissociation in CDCl₃.