A new tricarbonyl fac-[M(acac)(isc)(CO)3] complex (M = Re, Tc) with acetylacetonate (acac) and isocyanide (isc) in a 2+1 combination

The synthesis and characterization of the neutral 2+1 mixed ligand complex fac-Re(CO)₃(acac)(isc) (4) with acetylacetonate (acac) as the bidentate ligand and an isocyanide (the isocyanocyclohexane, isc) as the monodentate ligand is described. The synthesis of 4 proceeds through the intermediate formation of the fac-Re(acac)(H₂O)(CO)₃ precursor complex 2. Complex 4 was characterized by elemental analysis, spectroscopic methods, and X-ray crystallography showing a distorted octahedral arrangement of the ligands around Re. At technetium-99m level, the corresponding fac-^99mTc(acac)(isc)(CO)₃ complex 5 was obtained in high yield by reacting the fac-^99mTc(acac)(H₂O)(CO)₃ precursor complex 3 with isocyanocyclohexane and its structure was established by chromatographic comparison with the prototypic rhenium complex using high performance liquid chromatography.     

Ethylenediamine- and propylenediaminediacetic acid derivatives as ligands for the “fac-[M(CO)3]” core (M = Re, Tc)

The reaction of Re(CO)₅Cl with o- or p-N-(nitrophenyl)ethylenediaminediacetic acid (H₂L¹, H₂L²) and o- or p-N-(nitrophenyl)propylenediaminediacetic acid (H₂L³, H₂L⁴) in methanol leads to the formation of stable anionic [Et₃NH][Re(CO)₃(L)] · H₂O complexes 1-4. These compounds have been characterized by means of IR, mass spectrometry, elemental analysis, NMR and conductimetry, as well as X-ray crystallography for 2 and 3. The [Re(CO)₃]⁺ moiety is coordinated via the nitrogen of the iminodiacetic acid unit and two oxygens of monodentate carboxylate groups. In each case, the nitro group of the aromatic ring remains uncoordinated. The analogous technetium-99m complexes 1′ and 3′ were also prepared quantitatively by the reaction of H₂L¹ and H₂L³, respectively, with the fac-[^99mTc(CO)₃(H₂O)₃]⁺ precursor in ethanol. The corresponding Re and ^99mTc compounds were shown to possess the same structure by means of HPLC studies. The high affinity of these ligands for the Tc(I) or Re(I) core, coupled with the easiness of their derivatization (by reduction of the nitro group in amino group), implies that the utilization of this ligand system to develop target-specific radiopharmaceuticals for diagnosis and therapy is promising.     

Complexes with the fac-{M(CO)3} (M = Tc, Re) moiety and long alkyl chain ligands as Lipiodol surrogates

Accumulation of radiopharmaceuticals in the liver is frequently observed and represents in general a limiting factor when developing novel labeled compounds for any purpose in nuclear medicine. Aiming at the treatment of liver cancer with radiopharmaceuticals, such accumulation is desired but the compounds have to remain in the liver over an extended time period rather than being washed out or redistributed over time in the whole body. Lipiodol is known to remain in the liver and we present here a study for the preparation of ¹⁸⁶Re and ^99mTc labeled Lipiodol surrogates expected to behave similarly. We have synthesized two bidentate and two tridentate ligands conjugated to a pendant C18 chain as well as their corresponding fac-[Re(CO)₃]⁺ and fac-[Tc(CO)₃]⁺ complexes. Three of the rhenium complexes have been structurally characterized. Labelling with [¹⁸⁶Re(OH₂)₃(CO)₃]⁺ and [^99mTc(OH₂)₃(CO)₃]⁺, respectively, gave yields in the range of 90%. The complexes could be extracted into Lipiodol due to their high lipophilicity and close structural relationship with the major components of Lipiodol. The complexes are stable in water and in Lipiodol for more than 24 h. These Lipiodol surrogates present new low-valent technetium and rhenium complexes for applications in liver cancer imaging and therapy.     

Ultrafast excited-state dynamics of photoisomerizing complexes fac-[Re(Cl)(CO)3(papy)2] and fac-[Re(papy)(CO)3(bpy)] (papy = trans-4-phenylazopyridine)

The character and dynamics of low-lying electronic excited states of the complexes fac-[Re(Cl)(CO)₃(papy)₂] and fac-[Re(papy)(CO)₃(bpy)]⁺ (papy = trans-4-phenylazopyridine) were investigated using stationary (UV-Vis absorption, resonance Raman) and ultrafast time-resolved (visible, IR absorption) spectroscopic methods. Excitation of [Re(Cl)(CO)₃(papy)₂] at 400 nm is directed to ¹ππ^∗(papy) and Re → papy ¹MLCT excited states. Ultrafast (?1.4 ps) intersystem crossing (ISC) to ³nπ^∗(papy) follows. Excitation of [Re(papy)(CO)₃(bpy)]⁺ is directed to ¹ππ^∗(papy), ¹MLCT(papy) and ¹MLCT(bpy). The states ³nπ^∗(papy) and ³MLCT(bpy) are then populated simultaneously in less then 0.8 ps. The ³MLCT(bpy) state decays to ³nπ^∗(papy) with a 3 ps time constant. ³nπ^∗(papy) is the lowest excited state for both complexes. It undergoes vibrational cooling and partial rotation around the -NN- bond, to form an intermediate with a nonplanar papy ligand in less than 40 ps. This species then undergoes ISC to the ground state potential energy surface, on which the trans and cis isomers are formed by reverse and forward intraligand papy rotation, respectively. This process occurs with a time constant of 120 and 100 ps for [Re(Cl)(CO)₃(papy)₂] and [Re(papy)(CO)₃(bpy)]⁺, respectively. It is concluded that coordination of papy to the Re center accelerates the ISC, switching the photochemistry from singlet to triplet excited states. Comparison with analogous 4-styrylpyridine complexes (M. Busby, P. Matousek, M. Towrie, A. Vl?ek Jr., J. Phys. Chem. A 109 (2005) 3000) reveals similarities of the decay mechanism of excited states of Re complexes with ligands containing -NN- and -CC- bonds. Both involve sub-picosecond ISC to triplets, partial rotation around the double bond and slower ISC to the trans or cis ground state. This process is about 200 times faster for the -NN- bonded papy ligand. The intramolecular energy transfer from the ³MLCT-excited ^∗Re(CO)₃(bpy) chromophore to the intraligand state of the axial ligand occurs for both L = stpy and papy with a comparable rate of a few ps.     

Carboxylate and dicarboxylate derivatives of [Et4N][Re2(CO)6(OR)3] (R = H or Me)

The ligand exchange reaction of the anionic binuclear rhenium complexes (R = H (1) or Me (2)) has been studied with the carboxylic acids; benzoic acid (3, 4, and 5), fumaric acid (6), and terephthalic acid (7). The exchange with benzoic acid can be controlled by stoichiometry to one, two, or three substitutions. The doubly (4) and triply (5) substituted complexes represent new structural motifs for the triply bridged Re₂(CO)₆ unit. The dicarboxylic acids fumaric and terephthalic bridge two dirhenium centers. Crystal structure determinations have been carried out for the new complexes synthesized.     

Reactions of the fac-[Re(CO)3] and [ReO] moieties with substituted benzothiazoles

The reaction of 2-(2-aminophenyl)benzothiazole (Habt) with [Re(CO)₅Br] led to the isolation of the rhenium(I) complex fac-[Re(Habt)(CO)₃Br] (1). With trans-[ReOCl₃(PPh₃)₂], the ligand Habt decomposed to form the oxofree rhenium(V) complex [Re(itp)₂Cl(PPh₃)] (2) (itp = 2-amidophenylthiolate). From the reaction of trans-[ReOBr₃(PPh₃)₂] with 2-(2-hydroxyphenyl)benzothiazole (Hhpd) the complex [Re^VOBr₂(hpd)(PPh₃)] (3) was obtained. Complexes 1-3 are stable and lipophilic. ¹H NMR and infrared assignments, as well as the X-ray crystal structures, of the complexes are reported.     

Synthesis, characterization and X-ray structure of several aryloxide and alkoxide derivatives of [Et4N][Re2(CO)6(OR)3] (R = H or Me)

The ligand exchange reaction of the anionic binuclear rhenium complexes (R = H (1) or Me (2)) has been studied with the arylalcohols 4-aminophenol (3, 4), 3-dimethylaminophenol (5), 3-cyanophenol (6) and 4-cyanophenol (7, 8) and the diol ethylene glycol (9). Complete exchange of the three hydroxy or methoxy ligands by aryl alcohols can be attained by heating the reaction mixture or allowing the mixture to stir for several days. Incomplete exchange is achieved by stoichiometric control of the incoming ligand and is complete within twelve hours. For the alkyl alcohol ethylene glycol complete exchange can be obtained in 8 h. Crystal structure determinations for several of these derivatives have been carried out.     

Synthesis of fac-[Os(CO)3(L)Me2] (L = THF or MeCN) and some reactions with PPh3 and trityl salts

The reaction of cis-[Os(CO)₄Me₂] with Me₃NO in the THF or MeCN yields the complexes fac-[Os(CO)₃(L)Me₂] (where L = THF or MeCN). Whereas the THF complex is unstable and only characterised spectroscopically, fac-[Os(CO)₃(MeCN)Me₂] has been isolated as a white solid and fully characterized by both analytical and spectroscopic methods. These complexes fac-[Os(CO)₃(L)Me₂] are shown to be useful intermediates. Thus, reaction with PPh₃ gives fac-[Os(CO)₃(PPh₃)Me₂] in good yield.Reactions of fac-[Os(CO)₃(L)Me₂] (L = CO or MeCN) with CPh₃PF₆ or B(C₆F₅)₃ have been investigated. Whereas cis-[Os(CO)₄Me₂] showed no reaction with either CPh₃PF₆ or B(C₆F₅)₃, the reaction of fac-[Os(CO)₃(MeCN)Me₂] with CPh₃PF₆ in CH₂Cl₂ occurred over 16 h at room temperature to give an unstable cationic product and CPh₃Me. The reaction was monitored by both IR and NMR spectroscopies. When this reaction of fac-[Os(CO)₃(MeCN)Me₂] was carried out in the presence of a trapping ligand such as MeCN, the stable cationic product [Os(CO)₃(MeCN)₂Me]⁺ could be isolated and identified spectroscopically.     

Reactivity of [MO] (M = Tc, Re) core towards 2-mercapto-1,3-azole ligands. Formation of a new organometallic complex of Re(IV) and X-ray crystal structures

Imidazole-2-thiol derivatives H₂L^1-3 (H₂L¹ = 1H-benzoimidazole-2-thiol, H₂L² = 5-methyl-1H-benzoimidazole-2-thiol, and H₂L³ = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted M(V) (M = Tc, Re) complexes of the type [AsPh₄]{[MOCl₂(H₂Lⁿ)₂(H₂O)]Cl₂} are formed when [MOCl₄]⁻ react with H₂L^1-3 in 1:2 stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh₄]{[TcOCl₂(H₂L¹)₂(H₂O)]Cl₂}. The coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule is in trans to the TcO multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted cationic species {[MO(H₂Lⁿ)₄]Cl₃}. These complexes can be also isolated by reaction of [MOCl₄]⁻ with an excess of ligand. No complex is obtained with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵). Ligand exchange reactions of [ReOCl₃(PPh₃)₂] with HL^4,5 have also been investigated. Treating the oxo-precursor with HL⁴ no product is isolated, while with HL⁵ the chelate oxo-compound [ReOCl₂(L⁵)(PPh₃)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl₃(L^5∗)(PPh₃)₂] is obtained when a slight excess of HL⁵ reacts with [ReOCl₃(PPh₃)₂] in refluxing benzene solution and in air. Geometry about the Re atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole ligand anion, the apical positions are occupied by two PPh₃. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL⁶ which contains the same heteroatoms of HL⁵ does not form an organometallic species, but forms the chelate oxo-Re(V) complex [ReOCl₂(L⁶)(PPh₃)]. The solid-state structure has been authenticated by X-ray crystallography.     

Raman and infrared spectroscopic and theoretical studies of dinuclear rhenium and osmium complexes, M2(O2CCH3)4X2 (M = Re, Os; X = Cl, Br)

Infrared, far-infrared and Raman spectra of Re₂(O₂CCH₃)₄X₂ (X = Cl, Br) and Re₂(O₂CCD₃)₄Cl₂ have been recorded. Assignments of the vibrational spectra of Os₂(O₂CCH₃)₄Cl₂ and its deuterated derivative have been completed together with the Re complexes on the basis of normal-coordinate analysis. Force constant calculation was made for the acetate ion as well as for a four-atomic unit (with the CH₃ and CD₃ groups considered as point masses) using optimized masses of 16.7, 17.8, 20.5 and 21.6 for ¹²CH₃, ¹³CH₃, ¹²CD₃ and ¹³CD₃ groups, respectively. The force constants of the acetate ion have been adopted to the starting force field of the M₂(O₂CCH₃)₄X₂ type complexes. The metal-halide (0.889, 0.997 and 1.286 N cm⁻¹) and metal-metal stretching (3.32, 3.34 and 3.57 N cm⁻¹) force constants were obtained for Re₂(O₂CCH₃)₄Cl₂Re₂(O₂CCH₃)₄Br₂ and Os₂(O₂CCH₃)₄Cl₂ complexes, respectively. It was shown that the so-called diatomic approximation in most cases overestimates the M-M stretching force constants by 30-40%. Much better correlation has been obtained to fit these force constants, which produced values very close to those obtained by full normal-coordinate calculations. The Re-Re stretching force constants showed a reasonable correlation with the Re-Re bond distances for 18 rhenium complexes.     

Synthesis and characterization of deuterium-labelled (fulvene)M(CO)3 complexes (M = Cr, Mo)

The preparation and characterization of a series of deuterium-labelled (fulvene)M(CO)₃ (M = Cr, Mo) complexes is reported. (η⁵-6-Dimethylaminofulvene-d₂)Cr(CO)₃ and (η⁵-6-dimethylaminofulvene-d₂)Mo(CO)₃ were obtained in high yields by reacting the deuterated fulvene ligands with (MeCN)₃M(CO)₃ (M = Cr, Mo). In addition, syntheses of 6,6-diphenylfulvene-d₁₀ and 6,6-diphenyl-1,2-benzofulvene-d₁₀ as well as the corresponding tricarbonylchromium complexes are described.     

BEDT-TTF salts of the unsymmetrical [M(tfadt)2] dithiolene complexes (M = Ni, Au; tfadt = S2C2(CN)(CF3))

Two closely related 1:1 salts are obtained upon electrocrystallization of BEDT-TTF (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) in the presence of the isosteric [M(tfadt)₂]⁻ dithiolene complexes (tfadt: 1-trifluoromethyl-2-cyano-1,2-dithiolato), which essentially differ by their spin state, S = 0 in [Au(tfadt)₂]⁻, S = 1/2 in [Ni(tfadt)₂]⁻. In both [BEDT-TTF][M(tfadt)₂] salts, the BEDT-TTF radical cations form chains with a strong lateral overlap and strong antiferromagnetic interactions while the paramagnetic anions in the nickel-containing salt [BEDT-TTF][Ni(tfadt)₂] are essentially non-interacting. The structural differences between the nickel and gold complexes are analyzed and discussed.     

Complexes of the fac-{Re(CO)3} core with tridentate ligands derived from arylpiperazines

Arylpiperazines, XC₆H₄N(CH₂CH₂)₂NH, are readily alkylated to give the N-alkylpiperazines of the type XC₆H₄N(CH₂CH₂)₂N(CH₂)_nNH₂. The amine functions of these derivatives are in turn easily subjected to mono- or dialkylation to provide potentially tridentate ligands of the types XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(H)(CH₂Y) and XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(CH₂Y)(CH₂Z), respectively. The latter class of dialkylated derivatives may be symmetrically (Y=Z) or unsymmetrically (Y ≠ Z) substituted. The donor groups Y and Z of this study include pyridine, imidazole, methyl-imidazole, thiazole, carboxylate and thiolate.The reactions of these ligands with [NEt₄]₂[Re(CO)₃Br₃] yield complexes of the type [Re(CO)₃{(YCH₂)N(H)(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ and [Re(CO)₃{(ZCH₂)(YCH₂)N(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ where the molecular charge n (0, +1, or +2) depends on the nature of the donor groups Y and Z (whether neutral or anionic or a combination of neutral and anionic) and on the degree of protonation of the piperazine unit (x=0 or 1; y=0 or 1). This variety of tridentate chelators provides complexes with fac-{Re(CO)₃N₃}, {Re(CO)₃N₂O}, {Re(CO)₃NO₂}, {Re(CO)₃N₂S} and {Re(CO)₃NS₂} coordination geometries. The structures of the model compound [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-piperidine}]Br · H₂O, [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(NC₅H₄CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(O₂CCH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}] · xCH₃OH (x≈0.875), [Re(CO)₃{(NC₅H₄CH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}]Br₂ · 2CH₂Cl₂ · H₂O and [Re(CO)₃{(CH₃N₂C₃H₂CH₂)(O₂CCH₂)NCH₂CH₂CH₂-CH₃OphenpipH₂}]BrCl · 1.5CH₃OH · H₂O are discussed (phenpip: phenylpiperazine, -C₆H₄N(CH₂CH₂)₂N-).     

TTF charge transfer salts containing cyanometallate anions [M(phen)(CN)4] (M = Cr or Fe; phen = 1,10-phenanthroline)

Two new charge transfer salts of TTF with the counter anions [M(phen)(CN)₄]⁻ (phen = 1,10-phenanthroline, M = Cr (I) and Fe (II)) are described. The structures consist of alternating stacks of dimerised TTF⁺ cations and [M(phen)(CN)₄]⁻ anions and they are linked together by many short S?S contacts and hydrogen bonds. Within the organic stack, two dimerised TTF⁺ cations are arranged in a slipped face-to-face mode with short intra-dimer and long inter-dimer S?S distances. Strong antiferromagnetic exchange was found in the TTF⁺ dimers. Conductivity measurements show that compound I is a semiconductor.     

Synthesis and characterization of [Fe(III)(qsal)2][M(III)(pds)2] (M = Cu, Au)

Salts of the Fe(III) spin crossover cation [Fe^III(qsal)₂]⁺ (qsalH = N-(8-quinolyl)salicylaldimine) and monoanions [M^III(pds)₂]⁻ (M = Cu, Au; pds = pirazine-2,3-diselenolate) with formula [Fe^III(qsal)₂][M^III(pds)₂] were prepared and characterized by single crystal X-ray diffraction and magnetic measurements. These two salts present magnetic properties essentially due to the Fe^III centres in the high-spin state (S = 5/2), and do not have any spin transition.     

Searching for switchable molecular conductors: Salts of [M(dcbdt)2] (M = Ni, Au) anions with [Fe(sal2-trien)] and [Fe(phen)3]

Salts of [Fe^III(sal₂-trien)]⁺and [Fe^II(phen)₃]²⁺ cations and M[(dcbdt)₂]⁻ anions with M = Ni and Au (dcbdt = dicyanobenzenedithiolate) with formula [Fe(sal₂-trien)] [M(dcbdt)₂] and [Fe(phen)₃] [M(dcbdt)₂]₂ were obtained and characterized by single X-ray diffraction and magnetic measurements. None of these salts shows a clear spin crossover behaviour and their magnetic properties are due essentially to the cations in a high spin S = 5/2 and low spin states for the Fe^III and Fe^II salts respectively. The magnetic Ni sublattices in both compounds appear to have a negligible direct contribution to the magnetization but enhance the AF interactions in the cation sublattice.     

A new bisphosphonate-containing <Superscript>99m</Superscript>Tc(I) tricarbonyl complex potentially useful as bone-seeking agent: synthesis and biological evaluation

Aiming to develop new bone-seeking radiotracers based on the organometallic core fac-[^99mTc(CO)₃]⁺ with improved radiochemical and biological properties, we have prepared new conjugates with phosphonate pendant groups. The conjugates comprise a chelating unit for metal coordination, which corresponds to a pyrazolyl-containing backbone (pz) with a N,N,N donor-atom set, and a pendant diethyl phosphonate (pz-MPOEt), phosphonic acid (pz-MPOH) or a bisphosphonic acid (pz-BPOH) group for bone targeting. Reactions of the conjugates with the precursor [^99mTc(H₂O)₃(CO)₃]⁺ yielded (mote than 95%) the single and well-defined radioactive species [^99mTc(CO)₃(κ³-pz-MPOEt)]⁺ (1a), [^99mTc(CO)₃(κ³-pz-MPOH]⁺ (2a) and [^99mTc(CO)₃(κ³-pz-BPOH)]⁺ (3a), which were characterized by reversed-phase high-performance liquid chromatography . The corresponding Re surrogates (1–3), characterized by the usual analytical techniques, including X-ray diffraction analysis in the case of 1, allowed for macroscopic identification of the radioactive conjugates. These radioactive complexes revealed high stability both in vitro (phosphate-buffered saline solution and human plasma) and in vivo, without any measurable decomposition. Biodistribution studies of the complexes in mice indicated a fast rate of blood clearance and high rate of total radioactivity excretion, occurring primarily through the renal–urinary pathway in the case of complex 3a. Despite presenting moderate bone uptake (3.04 ± 0.47% injected dose per gram of organ, 4 h after injection), the high stability presented by 3a and its adequate in vivo pharmacokinetics encourages the search for new ligands with the same chelating unit and different bisphosphonic acid pendant arms.     

Five-coordinate rhenium(III)-thiolato complexes: the structure of [Re(SCH2PhOCH3)3(PPh3)2]

A novel five-coordinate rhenium(III)-thiolato complex, Re(SCH₂C₆H₄OCH₃-p)₃(PPh₃)₂ has been isolated during the reaction of trans-ReOCl₃(PPh₃)₂ with p-methoxybenzyl mercaptan. In the unexpected structure that was acquired, the central metal has undergone a reduction from Re(V) to Re(III). The five-coordinate Re(III) complex has been characterized by spectroscopic methods, elemental analysis and X-ray crystallography. X-ray crystallographic studies showed the coordination geometry around rhenium to be that of a trigonal bipyramid. The basal plane is defined by three sulfur atoms of the monodentate ligand, while the two apical positions are occupied by two phosphines of the precursor.     

Kinetics study of the substitution reaction of fac-[Fe(CN)2(CO)3I] with PPh3

Substitution reaction of fac-[Fe^II(CN)₂(CO)₃I]⁻ with triphenylphosphine (PPh₃) produced mono phosphine substituted complex cis-cis-[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh₃. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻][PPh₃]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (k_BT/h)exp(−ΔH^≠/RT + ΔS^≠/R) with ΔH^≠ = 119(4) kJ mol⁻¹ and ΔS^≠ = 102(10) J mol⁻¹ K⁻¹. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).