Preparation of mononuclear and dinuclear Rh hydrotris(pyrazolyl)borato complexes containing arenethiolato ligands and conversion of the mononuclear complexes into dinuclear Rh-Rh and Rh-Ir complexes with bridging arenethiolato ligands

Reactions of [Tp*Rh(coe)(MeCN)](; Tp*= HB(3,5-dimethylpyrazol-1-yl)(3); coe = cyclooctene) with one equiv. of the organic disulfides, PhSSPh, TolSSTol (Tol = 4-MeC(6)H(4)), PySSPy (Py = 2-pyridyl), and tetraethylthiuram disulfide in THF at room temperature afforded the mononuclear Rh(III) complexes [Tp*Rh(SPh)(2)(MeCN)](3a), [Tp*Rh(STol)(2)(MeCN)](3b), [Tp*Rh(eta(2)-SPy)(eta(1)-SPy)](6), and [Tp*Rh(eta(2)-S(2)CNEt(2))(eta(1)-S(2)CNEt(2))](7), respectively, via the oxidative addition of the organic disulfides to the Rh(I) center in 1. For the Tp analogue [TpRh(coe)(MeCN)](2, Tp = HB(pyrazol-1-yl)(3)), the reaction with TolSSTol proceeded similarly to give the bis(thiolato) complex [TpRh(STol)(2)(MeCN)](4) as a major product but the dinuclear complex [[TpRh(STol)](2)(micro-STol)(2)](5) was also obtained in low yield. Complex 3 was treated further with the Rh(III) or Ir(III) complexes [(Cp*MCl)(2)(micro-Cl)(2)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the thiolato-bridged dinuclear complexes [Tp*RhCl(micro-SPh)(2)MCp*Cl](8a: M = Rh, 8b: M = Ir). Dirhodium complex [TpRhCl(micro-STol)(2)RhCp*Cl](9) was obtained similarly from 4 and [(Cp*RhCl)(2)(micro-Cl)(2)]. Anion metathesis of 8a proceeds only at the Rh atom with the Cp* ligand to yield [Tp*RhCl(micro-SPh)(2)RhCp*(MeCN)][PF(6)](10), when treated with excess KPF(6) in CH(2)Cl(2)-MeCN. The X-ray analyses have been undertaken to determine the detailed structures of 3b, 4, 5, 6, 7, 8a, 9, and 10.     

Synthesis and characterisation of dinuclear and mononuclear Cobalt (II) benzoate complexes

Aqua-bridged binuclear cobalt (II) benzoate complexes having pyridine as auxiliary ligands are synthesised through solid state reactions and characterised. The binuclear core in these complexes comprise of two bridging benzoates and an aqua bridge. Each of the cobalt (II) centre is further co-ordinated to one benzoate and two pyridine ligands. The aqua-bridged cobalt (II) benzoate complex [Co₂(μ-H₂O)(μ-OBz)₂(OBz)₂(Py)₄] ·  (C₆H₆)(BzOH) (1a) is inclusion compounds with benzoic acid and benzene (where OBz  =  benzoate, py  =  pyridine). Analogous complex [Co₂(μ-H₂O)(μ-OBz)₂(OBz)₂(Py)₄] · 1.5(C₆H₆) without benzoic acid included is also prepared by an alternative method and structurally characterised. Analogous aqua-bridged complex derived from p-chlorobenzoic acid in unsolvated form is characterised. The Co–O–Co separation in these complexes is in the range of 3.55–3.64 Å with angles Co–O–Co varying from 111.8° to 116.4°. While similar reaction in solution leads to the formation of mononuclear complex having composition [Co(OBz)₂(Py)₂(H₂O)]. The unsubstituted benzoate complex 1a can be easily oxidised to form a tetrameric cobalt (III) complex having benzoate and oxo-bridged structure with a Co₄O₄ core.     

Formation and characterization of mononuclear and dinuclear manganese oxide-dioxygen complexes in solid argon

A manganese atom reacts with dioxygen to form the previously characterized MnO 2 molecule in solid argon under UV-visible light irradiation. Subsequent sample annealing allows the dioxygen molecules to diffuse and to react with MnO 2 to give the (eta (2)-O 2)MnO 2 complex, which is characterized to be a side-on bonded peroxo manganese dioxide complex. The manganese tetraoxide MnO 4, which was predicted to be less stable than the (eta (2)-O 2)MnO 2 isomer, was not observed. However, the (eta (2)-O 2)MnO 2 complex reacts with another weakly coordinated dioxygen to give the (eta (2)-O 2)MnO 4 complex via visible light irradiation, in which the manganese tetraoxide is coordinated and stabilized by a side-on bonded O 2 molecule. Manganese dimer reacts with dioxygen to form the cyclic Mn(mu-O) 2Mn cluster spontaneously upon annealing, which further reacts with dioxygen to give the (eta (2)-O 2) 2Mn(mu-O) 2Mn cluster, a side-on bonded disuperoxide complex with a planar D 2 h structure.     

Synthesis,characterization, and antitumor activity of mononuclear and dinuclear ruthenium complexes

Abstract

Dinuclear ruthenium complexes [Ru₂(bpy)₄BL](ClO₄)₂ (Ru-1), where bpy = 2,2′-bipyridine and BL = 2,2′-((1E,1′E)-((E)-diazene-1,2-diyl-bis(2,1-phenylene))-bis(azanylylidene))bis(methanylylidene))diphenol (a bidentate bridging ligand), and mononuclear ruthenium complexes [Ru(bpy)₂L](ClO₄) (Ru-2), where L = (E)-2-((phenylimino)methyl)phenol, were synthesized and characterized by elemental analysis and electrospray ionization mass spectrometry. Their photophysical and electrochemical properties were also studied. The cytotoxicity of the two complexes in vitro was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results indicated that Ru-1 and Ru-2 exhibited significant dose-dependent cytotoxicity to human breast cancer (MCF-7), gastric cancer (SGC-7901), cervical cancer (Hela), and lung cancer (A549) tumor cell lines. Ru-1 showed excellent antitumor effects in a cellular study (IC₅₀ values of 3.61 μM for MCF-7 human breast cancer cells in vitro). However, Ru-2 exhibited the highest cytotoxicity to Hela cells; the IC₅₀ value is 3.71 μM. The results reveal that Ru-1 and Ru-2 have obvious selectivity and might be a potential anticancer agent that could improve the efficacy of common anticancer therapies.     

Unusual dinuclear and mononuclear cyclometalated iridium complexes of 2,5-diaryl-1,3,4-oxadiazole derivatives

A family of new 2,5-diphenyl-1,3,4-oxadiazole (OXD) derivatives 8-11 bearing ortho-alkyl substituents on one of the phenyl rings is reported. The reactions of these OXDs with IrCl(3) under standard cyclometalating conditions did not give the usual μ-dichloro bridged diiridium OXD complexes. Instead, the novel diiridium complexes 12-14 and the monoiridium complex 15 were isolated and characterized by X-ray crystallography. It is proposed that the unusual structures arise because of the ortho-alkyl substituents leading to a substantial twisting of part of the OXD system which, for steric reasons, changes the normal course of the metal-ligand coordination reactions. Subsequent reactions of 13 and 15 gave the mononuclear complexes 16-18 with acac and picolinate anciliary ligands. The crystal structures of 16 and 18 are reported. Photoluminescence is observed in the green (16) and blue-green regions (17 and 18) at room temperature. Complexes 16-18 are phosphorescent at low temperature, with triplet lifetimes of 4.2-5.7 μs at 77 K.     

Studies of bicarbonate binding by dinuclear and mononuclear Ni(II) complexes

Bicarbonate ion reacts with the dinuclear nickel(II) complex containing the taec ligand (taec = N,N',N' ',N' '-tetrakis(2-aminoethyl)-1,4,8,11-tetraazacyclotetradecane) in buffered aqueous solution to form the mu-eta(2),eta(2)-carbonate complex with a large effective binding constant for bicarbonate ion, log K(B) = 4.39 at pH = 7.4. In contrast, the dinuclear nickel(II) complex containing the o-xyl-DMC(2) ligand (o-xyl-DMC(2) = alpha,alpha'-bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene) does not react with bicarbonate or carbonate ion in aqueous solution. In propylene carbonate, the reaction of [Ni(2)(o-xyl-DMC(2))](4+) with bicarbonate proceeds rapidly to form the mu-eta(1),eta(1)-carbonate complex. The structure of this carbonate complex has been determined by an X-ray diffraction study that confirms the mu-eta(1),eta(1)-carbonate binding mode. A mononuclear analogue of [Ni(2)(taec)](4+), [Ni(2,3,2-tetraamine)](2+) does not form a detectable mononuclear or dinuclear product with bicarbonate ion in aqueous solution, but [NiDMC](2+) (DMC = 5,7-dimethyl-1,4,8,11-tetraazacyclotetradecane) reacts slowly with carbonate ion in aqueous solution to form a 2:1 complex.     

Synthesis,spectroscopic, magnetic properties and MMX force field study of two imidazolate-bridged dinuclear copper(II) complexes

Two new imidazolate-bridged dinuclear Cu^II complexes, Na[Cu₂(L¹)₂(im)] and K[Cu₂(L²)₂(im)] (where H₂L¹=6-amino-1,3-dimethyl-5(2-carboxyphenyl)azouracil and H₂L²=1,3-dimethyl-5(2-carboxyphenyl)azobarbituric acid) have been prepared and characterized by magnetic susceptibility and spectroscopic measurements. Both compounds exhibit the expected antiferromagnetic behaviour with 2J=−54.8 and −30.4 cm⁻¹, respectively. Because of the lack of suitable crystals for single crystal X-ray analysis, we have calculated the lowest energy structures using a program based on the MMX force field. On the basis of the results, the magnitude of the magnetic interaction is discussed. TMC 2623     

Selective oxidation of organic sulfides by mononuclear and dinuclear peroxotungsten(VI) complexes

Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in high yields at room temperature using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a variation of reaction conditions. The compounds could also effectively catalyze oxidation of sulfides by H₂O₂ to selectively yield sulfone with reasonably good turnover frequency (TOF).     

XAFS studies of anti-inflammatory dinuclear and mononuclear Zn(II) complexes of indomethacin

Zinc K-edge X-ray absorption fine structure (XAFS) experiments were performed in the solid and solution states at low temperature (10 K), on dimeric and monomeric anti-inflammatory Zn(II) complexes of indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid=IndoH] of the formula [Zn2(Indo)4L2] [L=pyridine (Py), N,N-dimethylacetamide (DMA)], [Zn(Indo)2L2] [L=ethanol (EtOH), methanol (MeOH)], and Zn(II) acetate dihydrate [Zn(OAc)2(OH2)2]. The bond distances and angles obtained from multiple-scattering fits to the XAFS data of the Zn(II) dimeric complexes in the solid and solution states exhibit excellent correspondence with those obtained from single crystal diffraction studies. The Zn...Zn separations of 2.97 and 2.96 A and carboxylate group O-C-O angles of 125 degrees for powdered [Zn2(Indo)4(Py)2] and [Zn2(Indo)4(DMA)2] agree well with the XRD values of 2.969(1) and 2.9686(6) A and 125.8(4) degrees and 126.1(2) degrees, respectively. The calculated Zn-O(RCOO) and Zn-L bond distances of 2.03 and 2.04 A, or 2.02 and 1.98 A for Py or DMA complexes, respectively, also agree well with crystallographic data. The X-ray powder diffraction data on samples of the monomers exhibited additional reflections apart from those due to the crystallographically characterized cis-[Zn(eta2-O,O'-Indo)2L2], but microanalyses were consistent with this formulation. Therefore, mixed models that contained the cis complex and a second component consisting of a trans-six-coordinate complex, a five-coordinate complex, or a four-coordinate complex were used to model the XAFS. The best fits to the XAFS data were obtained with a mixture of the cis-six-coordinate complex and a four-coordinate complex containing two monodentate Indo ligands. The bond lengths for the six-coordinate structure were consistent with those determined on a single crystal, and those for the four-coordinate complexes were consistent with related four-coordinate structures with two monodentate carboxylate ligands. Dissolution of the dimer (DMA adduct) in DMF resulted in a mixture of dimer and monomer species as shown by MS XAFS fitting. This is the first time that solution structures have been determined for anti-inflammatory Zn(II) complexes, and this is an important first step in understanding the pharmacology of the complexes.     

A copper thiolate centre for electron transfer: mononuclear vs. dinuclear complexes

We have structurally and spectroscopically investigated a rare example of a mononuclear aliphatic dithiolate Cu(II) complex characterized by a reversible Cu(II)/Cu(I) redox couple. By DFT, we have shown that this system has a lower reorganization energy than its previously described bis(μ-thiolato) dicopper parent complex, which reversibly cycles between the Cu(1.5)Cu(1.5) and Cu(I)Cu(I) redox states.     

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N₃)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh₃) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N₃ [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N₃^?) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N₃^? ligand directly connected to the platinum center, complex [Pt (bhq)(N₃)(PPh₃)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH₂Cl₂ and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N₃, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N₃)(P)] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂]). It is indicative of the determining role of the N₃^? ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed ³ILCT/³MLCT (intramolecular) and also from aggregations (intermolecular).     

Iridium(III) soft salts from dinuclear cationic and mononuclear anionic complexes for OLED devices

Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety.     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Mononuclear and dinuclear complexes of isoeilatin

This work describes the synthesis and characterization of mononuclear and dinuclear Ru(II) and Os(II) complexes based on the symmetrical bridging ligand isoeilatin (1). The crystal structure of 1.[HCl]2 consists of layers of tightly pi-stacked molecules of the biprotonated isoeilatin. The mononuclear complexes [Ru(bpy)2(ieil)]2+ (2(2+)) and [Os(bpy)2(ieil)]2+ (3(2+)) form discrete dimers in solution held together by face-selective pi-stacking interactions via the isoeilatin ligand. Coordination of a second metal fragment does not hinder the pi-stacking completely, as demonstrated by the concentration dependence of the 1H NMR spectra of the dinuclear complexes [{Ru(bpy)2}2{mu-ieil}]4+ (4(4+)), [{Os(bpy)2}2{mu-ieil}]4+ (5(4+)), and [{Ru(bpy)2}{mu-ieil}{Os(bpy)2}]4+ (6(4+)) and supported by the solid-state structure of meso-4.[Cl]4. The bridging isoeilatin ligand conserves its planarity even upon coordination of a second metal fragment, as demonstrated in the solid-state structures of meso-4.[Cl]4, meso-4.[PF6]4, and meso-5.[PF6]4. All of the dinuclear complexes exhibit a preference (3/2-3/1) for the formation of the heterochiral as opposed to the homochiral diastereoisomer. Absorption spectra of the mononuclear complexes feature a low-lying dpi(M) --> pi*iel MLCT band around 600 nm that shifts to beyond 700 nm upon coordination of a second metal fragment. Cyclic and square-wave voltammetry measurements of the complexes exhibit two isoeilatin-based reduction waves that are substantially anodically shifted compared to [M(bpy)3]2+ (M = Ru, Os). Luminescence spectra, quantum yields, and lifetime measurements at room temperature and at 77 K demonstrate that the complexes exhibit 3MLCT emission that occurs in the IR region between 950 and 1300 nm. Both the electrochemical and photophysical data are consistent with the low-lying pi orbital of the isoeilatin ligand. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the bridging isoeilatin ligand.     

Discrete dinuclear cyano-bridged complexes

The cyano-bridged complexes [L14CoIIINCFeII(CN)5]-, [L14CoIIINCFeIII(CN)5], [L15CoIIINCFeII(CN)5]-, and [L15CoIIINCFeIII(CN)5] (L14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6- amine, L15 = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) are prepared and characterized both structurally and spectroscopically. In each complex, the pendant amine is trans to the bridging CN ligand, as determined by spectroscopy and X-ray crystallography: Na(trans-[L14CoIIINCFeII(CN)5]).8H2O, monoclinic space group P2(1)/c, a = 15.58(1) A, b = 19.797(4) A, c = 19.830(6) A, beta = 91.62(4) degrees, Z = 8; trans-[L14CoIIINCFeIII(CN)5].4H2O, monoclinic space group P2(1)/m, a = 9.9690(9) A, b = 13.316(1) A, c = 10.1180(8) A, beta = 90.720(6) degrees, Z = 2; [L15CoIIINCFeIII(CN)5].4H2O, triclinic space group P1, a = 9.454(1) A, b = 9.778(1) A, c = 9.865(2) A, alpha = 60.37(1) degrees, beta = 62.60(1) degrees, gamma = 65.82(1) degrees, Z = 1. A precursor to the 14-membered macrocyclic complexes is prepared for the first time, and its crystal structure is also reported: trans-I [CoL14Cl](ClO4)2, orthorhombic space group Pbca, a = 11.833(3) A, b = 13.363(2) A, c = 26.015(2) A, Z = 8. These compounds form part of a novel series of discrete CN-bridged dinuclear compounds. The mixed-valent CoIII-FeII compounds exhibit metal-to-metal charge-transfer (MMCT) transitions in the region 510-530 nm.     

Molybdenum(VI) and molybdenum(V) mononuclear and dinuclear complexes with 1,3-diphenyl-1,3-propanedione

Summary The synthesis and the dinuclear or mononuclear nature of several molybdenum(VI) and molybdenum(V) oxocomplexes derived from 1,3-diphenyl-1,3-propanedione (HLL) are described. These complexes were identified by i.r. and electronic spectra, magnetic susceptibility and analytical data, and are assigned the following formulae: [MoO₂(LL)₂], [Mo₂O₅(LL)₂], [Mo₂O₄(LL)₂], [MoOCl(LL)₂], [MoCl₂(LL)] and [MoO(OH)(LL)₂)]. The low magnetic moments of the dinuclear complexes are due, in part, to intramolecular interactions. The i.r. data show that the dionate is bound by two oxygen atoms forming a chelate six-membered ring.     

Complexation, structure, and superoxide dismutase activity of the imidazolate-bridged dinuclear copper moiety with beta-cyclodextrin and its guanidinium-containing derivative

An imidazolate-bridged homodinuclear complex, {[Cu(L)(H2O)]2(im)}(ClO4)3 (1), assembled with beta-cyclodextrin (betaCD) and its guanidinium-containing derivative (betaGCD), and thus a helical inclusion complex, {[Cu(L)(H2O)(betaCD)]2(im)}(ClO4)3 (2), were successfully isolated and structurally characterized. Structural analysis showed that each Cu(II) ion has a distorted square pyramidal N4Ow coordination sphere and forms a chiral chain through hydrogen-bonding and hydrophobic interactions. The UV-vis data showed that such a chain can provide the imidazolate bridge additional stability and results in the dissociation equilibrium taking place at the physiological pH. The obtained IC50 value for 2 (0.23 muM) showed a high superoxide dismutase (SOD) activity, which corresponds to a highly stable imidazolate bridge. Interestingly, the guanidinium-containing 1/betaGCD system showed higher SOD activity (IC50 = 0.16 muM), which is enhanced at least by 30% in comparison with that of guanidinium-lacking 2. This result supports that the positive guanidinium plays a role in the catalytic mechanism of Cu,Zn-SOD by ensuring that superoxide enters and peroxide leaves rapidly from the coordination sphere of the copper ion.     

Synthesis and magnetism of 6-nitrobenzimidazolate and imidazolate-bridged copper(II) complexes

Summary Four new trinuclear copper(II) complexes, [Cu(phen)-(NBzIm)] (ClO₄) (1), [Cu(bpy)(NBzIm)](ClO₄) (2), [Cu-(Me₂-bpy)(NBzIm)](Ac)·1/2H₂O (3) and [Cu(Me₂-bpy)-(Im)](ClO₄)·1/2H₂O (4) (phen = 1, 10-phenanthroline, bpy = 2,2-bipyridine, NBzIm = 6-nitrobenzimidazolate ion, Im=imidazolate ion) have been prepared and characterized by variable temperature magnetic susceptibility measurements. A weak antiferromagnetic spin exchange interaction operates between copper(II) ions, exchange integrals evaluated as J =-23.82 cm^-1 for (1); and J=-21.91 cm^-1 for (2).     

Structures and magnetic properties of imidazolate-bridged tetranuclear and polymeric copper(II) complexes

Eight kinds of imidazolate-bridged copper(II) complexes were found to be classified into two categories from the magnetic properties. The crystal structures of [Cu(L)(μ-im)]_n (Him = imidazole; L = nonane-4,6-dionate, 2,6-dimethylheptane-3,5-dionate) and [Cu(L)(μ-im)]₄ (L = nonane-4,6-dionate, 1-phenylbutane-1,3-dionate) were determined, to reveal that they consist of polymeric chains and tetranuclear cycles, respectively. Note that the nonane-4,6-dionate derivative gave the two phases. The Bonner–Fisher model (a one-dimensional antiferromagnetic chain model) was plausibly applied to [Cu(L)(μ-im)]_n for the best fit, while a square model was to [Cu(L)(μ-im)]₄. The complexes with unknown crystal structures were also subjected to magnetic measurements, and the tetra- and polymeric structures could be clearly distinguished from each other by fitting the magnetic data to appropriate models. The exchange parameters were comparable for both series (2J/k_B = ?78 to ?97 K) because the structurally common bridges Cu–N(eq)–N(eq)–Cu afford comparable magnitudes of couplings.     

Unsymmetrical dinuclear cobalt and nickel trimethylacetate complexes

The reaction of the dinuclear complex Co₂(-OOCCMe₃)₂(²-OOCCMe₃)₂bpy₂ (1) with the polymer [Co(OH) _n (OOCCMe₃)_2–n ] _x afforded the unsymmetrical dinuclear complex bpyCo₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (2). The reaction of 2,2"-dipyridylamine with [Co(OH) _n (OOCCMe₃)_2–n ] _x gave rise to the analogous complex [(C₅H₄N)₂NH]Co₂(₂-O,²-OOCCMe₃)(-OOCCMe₃)₂(²-OOCCMe₃) (3). The reaction of complex 1 with Ni₄(₃-OH)₂(-OOCCMe₃)₄(OOCCMe₃)₂(MeCN)₂[²-o-C₆H₄(NH₂)(NHPh)]₂ (4) produced an isostructural heterometallic analog of complex 2 with composition bpyM₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (5) (M = Co, Ni; Co : Ni = 1 : 1) and the dinuclear heterometallic complex bpy(HOOCCMe₃)M(-OH₂)(-OOCCMe₃)₂M(OOCCMe₃)₂[o-C₆H₄(NH₂)(NHPh)] (6) (M = Co, Ni; Co : Ni = 0.15 : 1.85). Compounds 2 and 5 exhibit ferromagnetic spin-spin exchange interactions.