Dirhodium Units Research Articles

Experimental and theoretical study of dimer-of-dimers-type tetrarhodium(ii) complexes bridged by 1,4-benzenedicarboxylate linkers.

Two dimer-of-dimers-type tetrarhodium complexes, [Rh4(piv)6(BDC)] ([1]; piv = pivalate) and [Rh4(piv)6(F4BDC)] ([2]), in which two paddlewheel-type dirhodium units are linked by 1,4-benzenedicarboxylate (BDC) and 1,4-tetrafluorobenzenedicarboxylate (F4BDC), respectively, have been synthesized and characterized via single-crystal X-ray diffraction analyses, ESI-MS, 1H NMR, infrared spectroscopy, Raman spectroscopy, and elemental analyses. Crystal structure analyses of [1(THF)4] and [2(THF)4], which are crystallized from THF solutions of [1] and [2], respectively, revealed that dihedral angles (φ) between two -CO2 units and phenyl rings of the BDC linker in [1(THF)4] are almost co-planar (φ = 2.8°), whereas those of the F4BDC linker in [2(THF)4] are largely inclined (φ = 78.3°). Density functional theory calculations clarified that (i) their dihedral angles of optimized geometries of [1(THF)4] and [2(THF)4] are almost the same as their experimental geometries, and (ii) the rotation energy barriers of phenyl moieties in [1(THF)4] and [2(THF)4] estimated by potential energy surface analyses are 12.0 and 8.4 kcal mol-1, respectively, indicating that hydrogen bondings are formed between two -CO2 units and four hydrogen atoms of phenyl rings of the BDC linker in [1(THF)4], whereas two -CO2 units and four fluorine groups on the phenyl ring of the F4BDC linker in [2(THF)4] are electrostatically and sterically repulsed. Electrochemical properties and electronic structures of [1(THF)4] and [2(THF)4] are strongly influenced by the electronic states of dicarboxylate linkers, whereas absorption spectra are strongly influenced by the dihedral angles between two -CO2 units and phenyl rings of dicarboxylate linkers.

Crystal structures of tetrakis (hydroxyacetato)bis(dimethylsulfoxide) dirhodium(II)

Tetrakis(hydroxyacetato)bis(dimethyl sulfoxide)dirhodium(II) (1) is synthesized by the reaction of dimethyl sulfoxide (DMSO) with Rh2(OOCCH2OH)4. The complex is characterized by elemental analysis, FT-IR, ESI+-MS, 1H and 13C NMR, along with single crystal X-ray diffraction. The ambidentate DMSO ligands are bound to the rhodium center of 1 through their sulfur atoms, which is firstly predicated by its orange color, then confirmed by the observation of an increase in the S–O stretching frequencies, and finally, unambiguously determined by single crystal X-ray diffraction. The structure of 1 contains two similar but crystallographically independent molecules. Both molecules contain lantern dirhodium units, joined equatorially by four bidentate hydroxyacetate ligands and two monodentate DMSO axial ligands. Four hydrogen bonds link the molecules together with d(O⋯O) of 2.767(4)-2.824(4) A to form a three dimensional network.

Rhodium-Organic Cuboctahedra as Porous Solids with Strong Binding Sites.

The upbuilding of dirhodium tetracarboxylate paddlewheels into porous architectures is still challenging because of the inertness of equatorial carboxylates for ligand-exchange reaction. Here we demonstrate the synthesis of a new family of metal-organic cuboctahedra by connecting dirhodium units through 1,3-benzenedicarboxylate and assembling cuboctahedra as porous solids. Carbon monoxide and nitric oxide were strongly trapped in the internal cavity thanks to the strong affinity of unsaturated axial coordination sites of dirhodium centers.

Assembled structures of tetrakis(biimidazole)dirhodium complexes hydrogen-bonded with common inorganic anions.

Eight new structures of dirhodium complexes, each with four biimidazole (H2bim) ligands, were obtained: [Rh2(H2bim)4(H2O)2](NO3)4·4H2O (I), [Rh2(H2bim)4(H2O)2](ClO4)4·5H2O (II), [Rh2(H2bim)4(MeOH)2](ClO4)4 (III), [Rh2(H2bim)4(DMF)2](BF4)4 (IV), [Rh2(H2bim)4(Mepy)2](SiF6)2·8H2O (V), [{Rh2(H2bim)4(pz)}2(μ-pz)](SiF6)(ClO4)6·12.7H2O (VI), [{Rh2(H2bim)4(pz)}2(μ-pz)](ClO4)8·11.4H2O (VII) and [Rh2(H2bim)4(μ-pz)](SiF6)2·6H2O (VIII). The unbridged Rh-Rh bond distances range between 2.6313 (8) and 2.7052 (5) Å. The dirhodium units adopt a staggered conformation with torsion angles N-Rh-Rh-N of 37.6 (4)-48.98 (8)°. Various assembled structures were constructed by hydrogen bonding between the complexes and the anions: a discrete structure in (IV), one-dimensional structure in (II), two-dimensional structures in (I), (III), (VI), (VII) and (VIII) and a three-dimensional structure in (V).

Structural Diversity in Paddlewheel Dirhodium(II) Compounds through Ionic Interactions: Electronic and Redox Properties

Reactions of dinuclear rhodium(II) tetracarboxylates, [Rh2(O2CR)4] (R = Me, Et), with halides (Br– and I–) or pseudohalides (OCN–) yield dinuclear complexes with intriguing supramolecular architectures based on ionic interactions. The solid-state arrangement of the complexes presented here has been studied using single-crystal X-ray diffraction. Discrete anionic units with the axial positions occupied by isocyanate, Na2[Rh2(O2CMe)4(NCO)2]·4H2O (1), water and isocyanate, Na[Rh2(O2CMe)4(NCO)(H2O)] (2), iodide, {K2[Rh2(O2CEt)4I2]·H2O}n (3), and bromide ligands, {K2[Rh2(O2CEt)4Br2]·H2O}n (4) and K[Rh2(O2CEt)4(Br)0.5]2[Rh2(O2CEt)4(H2O)2] (5), have been found. Complex 1 shows monodimensional polymeric chains stabilized through ionic interactions, while complexes 2–4 consist of two-dimensional layers. Finally, a three-dimensional network containing two kinds of dirhodium moieties has been found in complex 5. Speciation of the [Rh2(O2CR)4]/X– (R = Me, Et; X = OCN, Br, I) systems was investigated in aqueous solution by UV–visible titrations, helping us to rationalize the obtention of different Rh–X stoichiometries in the crystal state. By cyclic voltammetry, we have evaluated the effect of X– coordination on the oxidation properties of these dirhodium(II) units.

Polymeric adducts of rhodium(II) tetraacetate with aliphatic diamines: natural abundance 13C and 15N CPMAS NMR investigations

Complexation properties of dimeric rhodium(II) tetracarboxylates have been utilised in chemistry, spectroscopy and organic synthesis. Particularly, the combination of these rhodium salts with multifunctional ligands results in the formation of coordination polymers, and these are of interest because of their gas-occlusion properties. In the present work, the polymeric adducts of rhodium(II) tetraacetate with flexible ligands exhibiting conformational variety, ethane-1,2-diamine, propane-1,3-diamine and their N,N'-dimethyl- and N,N,N',N'-tetramethyl derivatives, have been investigated by means of elemental analysis, (13)C CPMAS NMR, (15)N CPMAS NMR and density functional theory modelling. Elemental analysis and NMR spectra indicated the axial coordination mode and regular structures of (1 : 1)n oligomeric chains in the case of adducts of ethane-1,2-diamine, N,N'-dimethylethane-1,2-diamine N,N,N',N'-tetramethylethane-1,2-diamine and N,N,N',N'-tetramethylpropane-1,3-diamine. Propane-1,3-diamine and N,N'-dimethylpropane-1,3-diamine tended to form heterogeneous materials, composed of oligomeric (1 : 1)n chains and the additive of dirhodium units containing equatorially bonded ligands. Experimental findings have been supported by density functional theory modelling of some hypothetical structures and gauge-invariant atomic orbital calculations of NMR chemical shifts.

Two- and three-dimensional assembled structures constructed from amidate-bridged paddlewheel complexes with group 6 oxometallate ions

Monocationic acetamidate-bridged dinuclear units are two-dimensionally connected by axially coordinating group 6 oxometallate ions in the structures [{M2(acam)4}2(M'O4)] (M = Rh, Ru; M' = Cr, Mo, W; Hacam = acetamide). In these sheet structures, dinuclear units are connected to each other by NH...O hydrogen bonds. The sheets are also connected with NH...O hydrogen bonds. Amidate-bridged dirhodium units that have bulkier alkyl groups reacted with CrO4(2-) or MoO4(2-) give three-dimensional diamondoid structures [{Rh2(pram)4}2(CrO4)] · 1.08H2O, [{Rh2(pram)4}2(MoO4)] · 2.44H2O and [{Rh2(buam)4}2(MoO4)] (Hpram = propionamide; Hbuam = butyramide). In these structures the NH group of the amidate ligands hydrogen bonds with O atoms in metallate ions.

Dirhodium Paddlewheel with Functionalized Carboxylate Bridges: New Building Block for Self-Assembly and Immobilization on Solid Support

A new dirhodium(II,II) paddlewheel complex, [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)] (1), has been synthesized using a predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)benzoate. The target product has been crystallized from the acetone solution and structurally characterized as a bis-acetone adduct, [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)(OCMe(2))(2)]·C(6)H(14) (2). By utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, 1 can self-assemble to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform. The resulting [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)]·2C(6)H(5)Cl (3) and [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)]·2CHCl(3) (4) products have microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, 3 and 4 represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any exogenous ligands. In solution, the dangling ends of carboxylate bridges of 1 have been successfully utilized for condensation reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity.

MMX Chains and Molecular Species Containing Rh 2 n+ ( n = 4, 5, and 6) Units: Electrical Conductivity in Crystal Phase of MMX Polymers

The control of the experimental conditions in the reaction of Rh 2 (O 2 CCH 3 ) 4 with halides allows the isolation of the novel dirhodium complexes K x [Rh 2 X(O 2 CCH 3 ) 4 ] x ·4xH 2 O (X = Br, 1·4H 2 O and I, 2·4H 2 O) [Rh 2 (O 2 CCH 3 ) 4 Cl] x H 2 O (3·H 2 O), [Rh 2 (O 2 CCH 3 )Cl] x ·4xH 2 O (3·4H 2 O), and {Rh 2 (O 2 CCH 3 ) 4 I 2 ]· 4H 2 0 (4·4H 2 O) containing Rh 2 n+ (n = 4, 5 and 6) units. The X-ray structure determination of compounds 1-4 reveals the presence of dirhodium units in different oxidation states. The polyanionic complexes 1·4H 2 O and 2·4H 2 O containing Rh 2 4+ units give zig-zag chains. In contrast, the partially oxidized complexes 3·H 2 O and 3·4H 2 O containing Rh 2 5+ units are linked by chloride ligands forming linear chains. The first tetracarboxylatodirhodium(III) compound 4·4H 2 O is also described. Its structure consists of discrete binuclear [Rh 2 (O 2 CCH 3 ) 4 ] 2+ units with both axial positions occupied by iodide ligands. The very simple synthetic procedures presented here to achieve the partial or complete oxidation of the dirhodium(II) precursors open new perspectives in dirhodium complexes containing different oxidation states and in their potential applications in the construction of molecular devices. The electrical characterization of the polymer chains confirms conductivity in crystal phase. In addition, isolation of 1·4H 2 O and 2·4H 2 O on mica and morphological characterization of individual chains by atomic-force microscopy have been achieved.

Mo/Rh Carboxylate: Heterometallic Compound Built of Homometallic Paddlewheel Units

Mixed-metal molybdenum(II)/rhodium(II) tetra(trifluoroacetate) of the composition [(MoRh)(O2CCF3)4] has been obtained from the gas-phase reaction between volatile carboxylates, [Mo2(O2CCF3)4] and [Rh2(O2CCF3)4]. This is an interesting system for which a single-crystal X-ray investigation fails to provide an unambiguous evidence of whether the product consists of the initial homometallic or newly formed heterometallic paddlewheel units. In the solid-state structure both metal atoms occupy the same crystallographic position, while the M-M and M-O distances are averaged with respect to the parent homometallic compounds. Nevertheless, the results of mass-spectrometric and magnetic measurements clearly indicate that the title bimetallic carboxylate contains a statistical mixture of homometallic dimolybdenum and dirhodium units. The product can be considered as a result of cocrystallization of isomorphous paddlewheel molecules.

A Square-sheet Structure of Paddlewheel Dirhodium Complexes in Mixed Oxidation States with Perrhenate Linkers

Abstract A mixed oxidation-state (Rh24+ and Rh25+) complex, [{Rh2(acam)4}2(μ4-ReO4)] (1, Hacam = acetamide), was synthesized and characterized by X-ray structure analysis. A square-sheet structure is constructed from Rh2(acam)4 units and ReO4− ion linkers in which all dirhodium units are crystallographically equivalent. In the mixed oxidation-state compounds, the electrical conductivity of 1 (8.9 × 10−6 S cm−1) is higher than that of [{Rh2(acam)4}3(μ3-Cl)2]·4H2O, but lower than that of [{Rh2(acam)4}2(μ4-I)]·6H2O.

Gas-Phase Assembling of Dirhodium Units into a Novel Organometallic Ladder: Structural and DFT Study

A hydrocarbon that has three separate aromatic rings, namely 1,4-bis(p-tolylethyl)benzene (C24H26), has been structurally characterized for the first time and tested as an elongated aromatic π-donor in assembling reactions under solvent-free conditions. Its gas-phase interaction with the electrophilic dimetal complex, [Rh2(O2CCF3)4], affords single crystals of a novel organometallic complex, [Rh2(O2CCF3)4]2·(C24H26). The product has a ladder type structure built on weak but directional rhodium(II)−π-arene interactions. In the above framework, each C24H26 exhibits a tetradentate-bridging coordination having four rhodium(II) centers attached to the opposite sides of the two peripheral benzene rings. The underlying reasons for such coordination defining the formation of the title product have been discussed based on the results of density functional theory, namely the orbital interaction analysis of the reacting partners.

Chiral Organometallic Triangles with Rh−Rh Bonds. 1. Compounds Prepared from Racemic cis-Rh2(C6H4PPh2)2(OAc)2

Reaction of racemic cis-Rh(2)(C(6)H(4)PPh(2))(2)(OAc)(2)(HOAc)(2) with excess Me(3)OBF(4) in CH(3)CN results in the formation of racemic cis-[Rh(2)(C(6)H(4)PPh(2))(2)(CH(3)CN)(6)](BF(4))(2).0.5H(2)O (1.0.5H(2)O), an ionic dirhodium complex which has two cisoid nonlabile orthometalated phosphine bridging anions and six labile CH(3)CN ligands in equatorial and axial positions. Reactions of 1 with tetraethylammonium salts of the linear dicarboxylates, oxalate, terephthalate, and 4,4'-biphenyl-dicarboxylate, in organic solvents, produced racemic crystals of the triangular compounds [Rh(2)(C(6)H(4)PPh(2))(2)](3)(C(2)O(4))(3)(py)(6).6MeOH.H(2)O (2.6MeOH.H(2)O), [Rh(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)CO(2))(3)(DMF)(6).6.5DMF.0.5H(2)O (3.6.5DMF.0.5H(2)O), and [Rh(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)C(6)H(4)CO(2))(3)(py)(6).4.5CH(3)OH.0.75H(2)O (4.4.5CH(3)OH.0.75H(2)O), respectively. All compounds are electrochemically active. The relative chiralities of the dirhodium units in each triangle have been established using a combination of data from X-ray crystallography and (31)P NMR spectroscopy.

Tetraphosphinitoresorcinarene complexes — A new structural form of a rhodium(I) diphosphine complex

Tetrakis(diphenylphosphinito)resorcinarene ligands are shown to react with [Rh2(µ-Cl)2(CO)4] to give tetrarhodium(I) complexes in which there are two dirhodium units, each having the unprecedented structure syn-[Rh2(µ-Cl)2(CO)2P2], P = phosphinite donor.Key words: rhodium, resorcinarene, tetraphosphinite, carbonyl.

A diamondoid network of tetrakis(acetamidato)dirhodium in mixed oxidation states linked by mu4-iodide having a 10(5) enhancement of its electrical conductivity by water molecules of hydration.

A mixed oxidation-state (Rh24+ and Rh25+) compound, [{Rh2(acam)4}2I]n.6nH2O (Hacam = acetamide), has been synthesized. The compound has a nonpenetrating diamondoid arrangement of {Rh2(acam)4} units linked by mu4-iodides. All of the dirhodium units are crystallographically equivalent, as are all of the iodide atoms. The magnetic susceptibility of this compound shows that one-half of the Rh2 units are in the Rh25+ oxidation state with one odd electron and the other half in the closed-shell Rh24+ state. Its electrical conductivity is 1.4 x 10-3 S cm-1 (pellets, room temperature) and oscillates over the range of 105 orders of magnitude during dehydration-rehydration cycles of interstitial water molecules.

Powder diffraction study of a coordination polymer comprised of rigid building blocks: [Rh2(O2CCH3)4.mu2-Se2C5H8-Se,Se']infinity.

The crystal structure of a new hybrid product comprised of two rigid building blocks, namely dirhodium(II) tetraacetate, [Rh(2)(O(2)CCH(3))(4)] (1), and 2,6-diselenaspiro[3.3]heptane, Se(2)C(5)H(8) (2), has been solved ab initio using laboratory source X-ray powder diffraction (XRPD) data. The rigid body refinement approach has been applied to assist in finding an adequate model and to reduce the number of the refined parameters. Complex [Rh(2)(O(2)CCH(3))(4).mu(2)-Se(2)C(5)H(8)-Se,Se'] (3) conforms to the triclinic unit cell with lattice parameters of a = 8.1357(4), b = 8.7736(4), and c = 15.2183(8) A, alpha = 77.417(3), beta = 88.837(3), and gamma = 69.276(4) degrees, V = 989.66(8) A(3), and Z = 2. The centrosymmetric P space group was selected for calculations. The final values of the reduced wR(p), R(p), and chi(2) were calculated at 0.0579, 0.0433, and 5.95, respectively. The structure of 3 is a one-dimensional zigzag polymer built on axial Rh...Se interactions at 2.632(6) A. The 2,6-diselenaspiro[3.3]heptane ligand acts as a bidentate linker bridging dirhodium units via both selenium atoms. The geometrical parameters of individual groups for rigid body refinement have been obtained from X-ray powder data for dirhodium(II) tetraacetate (1) and from single-crystal X-ray diffraction for diselenium molecule 2. The crystal structures of 1 and 2 are reported here for the first time. For 1 indexing based on XRPD data has resulted in the triclinic unit cell P with lattice parameters of a = 8.3392(7), b = 5.2216(5), and c = 7.5264(6) A, alpha = 95.547(10), beta = 78.101(6), and gamma = 104.714(13) degrees, V = 309.51(5) A(3), and Z = 1. The final values were wR(p) = 0.0452, R(p) = 0.0340, and chi(2) = 1.99. The 1D polymeric motif built on axial Rh.O interactions of the centrosymmetric dirhodium units has been confirmed for the solid-state structure of 1. Compound 2,6-diselenaspiro[3.3]heptane (2) conforms to the monoclinic space group P2(1)/c with the unit cell parameters of a = 5.9123(4), b = 19.6400(13), and c = 5.8877(4) A, beta = 108.5500(10) degrees, V = 648.15(8) A(3), and Z = 4.

Structural Studies on the Stepwise Chelating Processes of Bidentate 2-(Aminomethyl)pyridine and Tridentate Bis(2-pyridylmethyl)amine toward an Acetate-Bridged Dirhodium(II) Center

Several intermediates and final products of the reactions of [Rh(2)(mu-CH(3)COO)(4)(CH(3)OH)(2)] with a tridentate ligand bis(2-pyridylmethyl)amine (bpa) and bidentate 2-(aminomethyl)pyridine (amp) have been isolated, and the chelation processes of these ligands to the dirhodium(II) center are discussed. The reaction of a 2 equiv amount of bpa in chloroform afforded three products, [Rh(2)(mu-CH(3)COO)(2)(eta(1)-CH(3)COO)(bpa)(2)](+) ([1]+), C(2)-[Rh(2)(mu-CH(3)COO)(2)(bpa)(2)](2+) ([2a](2+)), and C(s)-[Rh(2)(mu-CH(3)COO)(2)(bpa)(2)](2+) ([2b](2+)), where C(2) and C(s) denote the molecular symmetry of the two geometrical isomers. X-ray crystallography revealed that [1](+) contains ax-eq chelated bidentate and ax-eq-eq tridentate bpa and that [2a](2+) and [2b](2+) have two ax-eq-eq tridentate bpa ligands (ax denotes the site trans to the Rh-Rh bond, and eq, the site perpendicular to it). The reaction is initiated by almost instantaneous monodentate or inter-Rh(2)-unit bridging coordination of bpa at the ax sites, which is followed by very slow ax-eq chelate formation and then ultimate ax-eq-eq tridentate coordination. The reaction of [Rh(2)(mu-CH(3)COO)(4)(CH(3)OH)(2)] with amp in 1:2 ratio in chloroform initially gives an insoluble polymer in which amp interconnects the ax sites of the dirhodium(II) units. Further reactions afforded [Rh(2)(mu-CH(3)COO)(2)(eta(1)-CH(3)COO)(amp)(2)](+) ([4](+)) and [Rh(2)(mu-CH(3)COO)(2)(amp)(2)](2+) ([5](2)(+)). The X-ray structural studies show that [4](+) has one ax-eq and one eq-eq chelate and [5](2)(+) two eq-eq chelates. More rigid tridentate ligands 2,2':6',2"-terpyridine (tpy) and 4'-chloro-2,2':6',2"-terpyridine (Cl-tpy) have been introduced at ax sites in a monodentate mode ([Rh(2)(mu-CH(3)COO)(4)(tpy)(2)] (8) and [Rh(2)(mu-CH(3)COO)(4)(Cl-tpy)(2)] (9)). While the Rh-Rh distances of these complexes and [Rh(2)(mu-CH(3)COO)(2)(2,2'-bipyridine)(2)(py)(2)](2+) ([7](2)(+)) are practically unchanged (2.56-2.60 A) except for 8 and 9 (2.4 A), the Rh-N(ax) distances range from 2.11 to 2.35 A. Relatively short distances are found for the compounds with ax-eq or ax-eq-eq chelates (<2.22 A). Longest distances (2.32-2.35 A) found for 8 and 9 may be due to the steric effect. The distances of other complexes fall in the normal region. The visible band of the pi*(Rh-Rh) --> sigma*(Rh-Rh) transition in solid-state reflectance spectra shows a red-shift as the Rh[bond]N(ax) distances becomes longer.

A Honeycomb Network of a Paddlewheel-type Dirhodium Complex in Two Oxidation States and Pinning of the Oxidation States

Abstract The reaction of a mixture of [Rh2(acam)4(H2O)2] (Hacam = acetamide) and its radical cation salt with sodium chloride in an aqueous solution gave a mixed-valent 2-D honeycomb crystal of [{Rh2(acam)4}3(μ3-Cl)2]n·4nH2O. The oxidation states of the dirhodium units are pinned at each of the crystal sites by hydrogen bonding with solvate-water molecules.

Supramolecular assemblies of dimetal complexes with polydentate N-donor ligands: from a discrete pyramid to a 3D channel network.

Reactions of a dinuclear metal complex in the form of dirhodium(II) tetra(trifluoroacetate), [Rh(2)(O(2)CCF(3))(4)] (1), with a number of strong N-donor ligands having functional groups rigidly oriented at different directing angles have been found to yield supramolecular architectures of differing complexity. All structures have been established by X-ray crystallography. From reaction of 1 with neutral tris(4'-pyridyl)methylsilane ligand, CH(3)Si(C(5)H(4)N)(3) (L1), a discrete pyramid-shaped hexanuclear complex [[Rh(2)(O(2)CCF(3))(4)](3)CH(3)Si(C(5)H(4)N)(3)(eta(1)-C(6)H(6))(3)].C(6)H(6) (2.C(6)H(6)) has been isolated from benzene. In 2 three molecules of 1 are strongly coordinated to one L1 ligand at only one axial position of each dirhodium unit at the Rh-N distances of 2.152(6) A. The second rhodium atom of each dimetal complex in 2 weakly coordinates a benzene molecule with an Rh-C distance of 2.69(2) A. A supramolecular complex of the composition [[Rh(2)(O(2)CCF(3))(4)](2)(C(6)H(5))(2)Si(C(5)H(4)N)(2)] (3) has been prepared by reacting the dinuclear units 1 with a potentially bidentate ligand, bis(4'-pyridyl)diphenylsilane, (C(6)H(5))(2)Si(C(5)H(4)N)(2) (L2), having two pyridyl groups rigidly oriented at 109 degrees. In 3, one L2 ligand coordinates two dirhodium molecules 1 through their axial positions with the Rh-N distance of 2.150(5) A. An interesting extended 2D layered motif is formed by additional contacts of open axial positions of dirhodium units with phenyl groups of the neighboring ligands at Rh-C distances which average to 2.88(1) A. A supramolecular compound of the composition [[Rh(2)(O(2)CCF(3))(4)](3)(HO)C(C(5)H(4)N)(3)(eta(1)-C(6)H(6))].(1)/(2)C(6)H(6) (4.(1)/(2)C(6)H(6)) has been formed when linear dirhodium units 1 were reacted with tris(4'-pyridyl)methanol (L3) having tetrahedral directing angles that average to 110 degrees. A building block in the solid structure of 4 is a hexanuclear molecule in which one L3 ligand binds three dimetal units of 1 through N atoms of pyridyl groups at the average Rh-N distance of 2.143(7) A. A unique extended pseudo-3D structure in 4 is created by additional Rh-O coordination bonds as well as by weak metal-arene interactions.

Coupling dirhodium units through terpyridine bridges: synthesis and structure of a novel molecular rectangle

The cation [Rh2(μ-O2CMe)2(MeCN)6]2+ reacts with the bis-terpyridine ligand 2,3,5,6-tetra-2-pyridylpyrazine (tppz) to yield the reduced compound [Rh4(μ-O2CMe)2(tppz)2(MeOH)4]4+ whose structure is that of molecular rectangle with edges defined by short Rh–Rh and long Rh–tppz–Rh units.