A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Are methyl groups electron-donating or electron-withdrawing in boron clusters? Permethylation of o-carborane

That methyl groups attached to carbon atoms are electron donors must not be generally assumed. In boron clusters, Me groups on boron are electron withdrawing. At the B3LYP/6-31G* level of theory, it has been proven that the Mulliken charge on each boron after substitution of -H by -Me increases by +0.18 unit. This leads to a high build-up of positive charge upon permethylation, then hampering it. Experimentally, this is proven by the synthesis of 9-I0.707H0.293-12-Cl0.566H0.434-3,4,5,6,7,8,10,11-Me8-1,2-C2B10H2, in which positions 9 and 12 were first methylated and then attacked by nucleophiles. This is substantiated by the synthesis of 3,6,8,9,10,12-Me6-1,2-C2B10H6 under the same experimental conditions but with time control.     

A new type of anionic metal dicyanamide extended networks through [Cu(N4-macrocycle)]2+ cation templation. Structure and magnetic properties

Two isomorphous anionic metal dicyanamide extended systems [Cu(pCTH)][M(dca)(4)] (M = Mn(II), Co(II); dca = dicyanamide; pCTH = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetrazacyclotetradecane-4,11-diene) have been prepared through [Cu(pCTH)](2+) templation and characterized by X-ray crystallography and magnetic measurements. In these complexes, the [M(dca)(4)](2)(-) anions form 2D (4,4) distorted square-gridlike sheets in which each elongated octahedral M(N(dca))(6) metal center is connected to four neighboring ones through single dicyanamide bridges in equatorial positions. [Cu(pCTH)](2+) cations lie between the sheets and display weak bonding interactions with the axial dicyanamide ligands on the M centers of two neighboring [M(dca)(4)](n)()(2)(n)()(-) sheets, thus leading to a 3D heterometallic network. Variable-temperature magnetic measurements reveal weak antiferromagnetic interactions between metal centers across mu(1,5)-dicyanamide bridging ligands. For the cobalt(II) compound, the experimental data for T > 30 K match well with the calculated curve by taking into consideration the spin-orbit coupling effect for the (4)T(1g) ground state of the cobalt(II) and an axial distortion of the octahedral geometry. No long-range magnetic order was observed in these compounds above 2 K.     

Comparative study of NS(2)(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II)

Ligands LX of the type NS(2) with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO(4))(2).6H(2)O and [RuCl(2)(PPh(3))(3)] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO(4)](2), except for L5, and [RuCl(2)(LX)(PPh(3))], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2'-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl(2)(L5)(PPh(3))].2CCl(4) have been characterized by single-crystal X-ray diffraction methods.     

Redox potential modulation in mixed sandwich pyrrolyl/ dicarbollide complexes

Carbon cluster (C(c)) substituents have been shown to be of essential importance in C(c).C(c) distance, rotational energy barriers, and (11)B[(1)H] NMR chemical shift values in mixed pyrrolyl/dicarbollide cobalt complexes. In the present work, the influence of electronic properties of exo-cluster substituents upon redox potential values associated to the metallic central atom in mixed pyrrolyl/dicarbollide and dimethylpyrrolyl/dicarbollide cobalt complexes is discussed. With that purpose, two new neutral sandwich species, closo-[3-Co(eta(5)-NC(4)(CH(3))(2)H(2))-1,2-(C(6)H(5))(2)-1,2-C(2)B(9)H(9)] (2) and closo-[3-Co(eta(5)-NC(4)(CH(3))(2)H(2))-1-CH(3)-2-SCH(3)-1,2-C(2)B(9)H(9)] (3), have been synthesized and characterized by (1)H, (11)B, (11)B[(1)H], and (13)C[(1)H] NMR and IR spectroscopies, elemental analysis, and X-ray diffraction analysis. The redox potential (E(1/2)) of these complexes has been measured in nonpolar media and compared to values obtained for previously reported mixed complexes, incorporating alkyl, phenyl, thiophenyl, and thiomethyl exo-cluster substituents. The potential shift arising from the effect of these substituents has been discussed in terms of individual and average contribution. This last point is in the case of two identical substituting groups placed on both C(c) atoms, in which the contribution of the second introduced substituent has shown to be lower than that for the first one. The potential shift arising from the presence of methyl units on the pyrrolyl anion has also been determined.     

cis‐[1,2‐Bis(diisopropylphosphino‐κP)‐1,2‐dicarba‐closo‐dodecaborane]dichloroplatinum(II) dichloromethane hemisolvate

The asymmetric unit of the title complex, [PtCl₂(C₁₄H₃₈B₁₀P₂)]·0.5CH₂Cl₂ or cis‐[PtCl₂{1,2‐(PⁱPr₂)₂‐1,2‐C₂B₁₀H₁₀}]·0.5CH₂Cl₂, contains one disordered solvent mol­ecule and two mol­ecules of the complex, in which each Pt^II atom displays slightly distorted square‐planar coordination geometry. The P atoms connected to the cage C atoms are coordinated to the Pt^II atom. The Pt—P distances vary slightly [2.215 (3) and 2.235 (4) Å] and the Pt—Cl distances are equal [2.348 (3) and 2.353 (5) Å].     

Synthesis, reactivity and structural studies of carboranyl thioethers and disulfides

The equimolar reaction of 1-SH-2-R-1,2-closo-C2B10H10(R=Me, H, Ph) with KOH in ethanol produces the thiolate species [1-S-2-R-1,2-closo-C2B10H10]-. These react with iodine to give the disulfide bridged dicluster (1-S-2-R-1,2-closo-C2B10H10)2(R=H, Me, Ph) compounds as analytically pure, white and air-stable solids in high yield. Synthesis of monothioether bridged species is synthetically more difficult. In fact three procedures have been tested to obtain the thioether bridged dicluster compounds (2-R-1,2-closo-C2B10H10)2S (R=Me, H, Ph) but only (2-Me-1,2-closo-C2B10H10)2S was successfully synthesized and characterized. Attempts to produce mixed compounds (1-R-1,2-closo-C2B10H10)S(1-R'-1,2-closo-C2B10H10), R not=R', were unsuccessful. Deboronation reaction of this dicarboranylthioether lead, depending on the reaction conditions, to monoanionic [(2-Me-1,2-closo-C2B10H10)S(8-Me-7,8-nido-C2B9H10)]- or dianionic [(8-Me-7,8-nido-C2B9H10)2S]2- sulfur bridge anions. Deboronation of carboranyl disulfides gave the corresponding dianionic [(7-S-8-R-7,8-nido-C2B9H10)2]2-(R=H, Me, Ph) species. This reaction was very dependent, however, on the reaction conditions. With slight variation of the reaction conditions, splitting of the S-S bond leading to the thiolate species with retention of the closo cluster was also found. Carboranyl disulfides (1-S-2-R-1,2-closo-C2B10H10)2(R=H, Me, Ph) do not lead to thiosulfinates R-S(O)-S-R' by oxidation with H2O2 or I2 as organic disulfides do. This behaviour is attributed to the presence of the sulfur atom directly bonded to the carbon cluster that produces electronic transfer from the filled orbitals on the sulfur atom into the cage LUMO (largely located on the cage Cc-Cc bond). This causes a depletion of electron density on the sulfur, thence impairing sulfur oxidation, and facilitating S-S breaking. Crystal structures of monothioethers (2-Me-1,2-closo-C2B10H10)2S, [NMe4][(2-Me-1,2-closo-C2B10H10)S(8-Me-7,8-nido-C2B9H10)](the first example reported in the literature of a two cluster compound incorporating the closo C2B10 and the nido[C2B9]- moieties linked by a one member spacer) and disulfides (1-S-1,2-closo-C2B10H11)2, (1-S-2-Me-1,2-closo-C2B10H10)2, (1-S-2-Ph-1,2-closo-C2B10H10)2 are reported which support the behaviour of these species.     

Sulfur, tin and gold derivatives of 1-(2'-pyridyl)-ortho-carborane, 1-R-2-X-1,2-C2B10H10 (R = 2'-pyridyl, X = SH, SnMe3 or AuPPh3)

Reaction of the lithium salt of 1-(2'-pyridyl)-ortho-carborane, Li[1-R-1,2-C(2)B(10)H(10)](R = 2'-NC(5)H(4)), with sulfur, followed by hydrolysis, gave the mercapto-o-carborane, 1-R-2-SH-1,2-C(2)B(10)H(10) which forms chiral crystals containing helical chains of molecules linked by intermolecular S-H...N hydrogen bonds. The cage C(1)-C(2) and exo C(2)-S bond lengths (1.730(3) and 1.775(2)[Angstrom], respectively) are indicative of exo S=C pi bonding. The tin derivative 1-R-2-SnMe(3)-1,2-C(2)B(10)H(10), prepared from Li[1-R-1,2-C(2)B(10)H(10)] and Me(3)SnCl, crystallises with no significant intermolecular interactions. The pyridyl group lies in the C(1)-C(2)-Sn plane, oriented to minimise the NSn distance (2.861(3)[Angstrom]). The tin environment is distorted trigonal bipyramidal with axial N and Me. The gold derivative 1-R-2-AuPPh(3)-1,2-C(2)B(10)H(10), prepared from Li[1-R-1,2-C(2)B(10)H(10)] and AuCl(PPh(3)), reveals no NAu interaction in its crystal structure.     

Self-assembled cationic heterochiral honeycomb-layered metal complexes with the in situ generated pyrimidine-2-carboxylato bisdidentate ligand. Hydrothermal synthesis, crystal structures, magnetic properties, and theoretical study of [M2(micro-pymca)3]OH.H2O (M = FeII, CoII)

The hydrothermal reaction of 2-cyanopyrimidine and either CoCl2.6H2O or FeCl2.4H2O affords 2D isostructural coordination polymers [M2(micro-pymca)3]OH.H2O ((M = CoII (1) and FeII (2) pymca = pyrimidine-2-carboxylato). The bisdidentate ligand (pymca) that can be considered an intermediate between bipyrimidine and oxalato is generated in situ from the hydrolysis of 2-cyanopyrimidine. The structure of 1 and 2 consists of heterochiral (6,3) honeycomb layers, crystal water molecules, and OH- anions, the latter playing a template and balancing charge role in the structure. Both compounds exhibit antiferromagnetic interactions between metal ions through the pyrimidine-2-carboxylate bridging ligand. Compound 1 is a spin-canted antiferromagnet leading to weak ferromagnetism at Tc < 10 K with a coercitive field of 580 Oe, whereas compound 2 is an antiferromagnet with TN = 21 K. Fit of the variable-temperature magnetic susceptibility data of 2 to the empirical equation for a regular honeycomb with S = 1 derived from Monte Carlo simulations leads to the following parameters: J = -4.57(2) cm-1 and g = 2.300(4). Density functional calculations have been used to explain the magnetic coupling in 2.     

A novel 3D cyano-bridged mixed-valence CoII/CoIII canted antiferromagnet constructed from defective cubanes. Synthesis, X-ray structure and magnetic properties

The hydrothermal reaction of 2-pyrimidine-carboxamide, CoCl2.6H(2)O and K3[Co(CN)6] affords a novel mixed-valence Co(II)/Co(III) 3D complex K[Co3(CN)6(ox)(H(2)O)2].H2O, which contains cyano-bridged Co(7) defective cubanes connected by oxalate and cyanide bridging groups and behaves as a canted antiferromagnet with Tc = 17.5 K.