Structure and magnetism of [M3](6/7+) metal chain complexes from density functional theory: analysis for copper and predictions for silver.

The ground-state electronic structure of the trinuclear complex Cu3(dpa)4Cl2 (1), where dpa is the anion of di(2-pyridyl)amine, has been investigated within the framework of density functional theory (DFT) and compared with that obtained for other known M3(dpa)4Cl2 complexes (M = Cr, Co, Ni) and for the still hypothetical Ag3(dpa)4Cl2 compound. Both coinage metal compounds display three singly occupied x2-y2-like (delta) orbitals oriented toward the nitrogen environment of each metal atom, generating antibonding M-(N4) interactions. All other metal orbital combinations are doubly occupied, resulting in no delocalized metal-metal bonding. This is at variance with the other known symmetric M3(dpa)4Cl2 complexes of the first transition series, which all display some delocalized bonding through the metal backbone, with formal bond multiplicity decreasing in the order Cr > Co > Ni. An antiferromagnetic coupling develops between the singly occupied MOs via a superexchange mechanism involving the bridging dpa ligands. This magnetic interaction can be considered as an extension to the three aligned Cu(II) atoms of the well-documented exchange coupling observed in carboxylato-bridged dinuclear copper compounds. Broken-symmetry calculations with approximate spin projection adequately reproduce the coupling constant observed for 1. Oxidation of 1 removes an electron from the magnetic orbital located on the central Cu atom and its ligand environment; 1+ displays a much weaker antiferromagnetic interaction coupling the terminal Cu-N4 moieties via four ligand pathways converging through the x2-y2 orbital of the central metal. The silver homologues of 1 and 1+ display similar electronic ground states, but the calculated magnetic couplings are stronger by factors of about 3 and 4, respectively, resulting from a better overlap between the metal centers and their equatorial ligand environment within the magnetic orbitals.

Cyclic polyamidato dianions as bridges between Mo(2)(4+) units: synthesis, crystal structures, electrochemistry, absorption spectra, and electronic structures.

Compounds in which quadruply bonded Mo(2)(4+) units, Mo(2)(DAniF)(3) (DAniF = N,N'-di-p-anisylformamidinate), are linked by cyclic diamidate anions have been synthesized and characterized by X-ray crystallography and spectroscopic methods. As identified by the diamidate linker, these compounds are 4,6-dioxypyrimidinate (2), 2,3-dioxypyrazinate (3), 2,3-dioxyquinoxalinate (4), 2,3-dioxy-5,6-dicyanopyrazinate (5), and cyanurate (6). With uracilate, a dinuclear unlinked 1:1 adduct is formed, Mo(2)(DAniF)(3)(uracilate) (1). The cyclic voltammograms of 3-5 reveal significantly larger DeltaE(1/2) values (258 mV-308 mV) than that of the oxalate linked analogue (212 mV), which is indicative of greater charge delocalization in the mixed valent Mo(2)(4+)/Mo(2)(5+) species and hence greater communication between the two Mo(2) units. DeltaE(1/2) for 2 is substantially lower than those for 3-5. This difference is attributed to the meta disposition of the two amidate groups in 4,6-dioxypyrimidinate as compared to their ortho arrangement in the pyrazinate-type linkers. The absorption spectra of the linked compounds 3-5 are more complex than those of the analogous polyunsaturated dicarboxylate linked compounds and reveal at least two significant absorption bands within the region 420-550 nm. Compound 2 also has two bands but with significantly lower intensity. Time dependent DFT calculations upon 2 and 3 indicate rather different electronic structures for these two structural isomers. The two bands for 3 have delta --> pi character, and the pi type orbitals have substantial contributions from the Mo(2) units as well as from the diamidate linker. The excitations observed in 2 are mainly metal based. The differences between the electronic spectra of 2 and 3 are consistent with the electrochemistry in underscoring the profound physical effect of changing the symmetry of the diamidate linker.

Mixed chloride/phosphine complexes of the dirhenium core. 10. Redox reactions of an edge-sharing dirhenium(III) non-metal-metal-bonded complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4).

Reduction and oxidation reactions of the dirhenium(III) non-metal-metal-bonded edge-sharing complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4) (1), have been studied. Several new mono- and dinuclear rhenium compounds have been isolated and structurally characterized in the course of this study. Reductions of 1 with 1 and 2 equiv of KC(8) result in an unusual face-sharing complex having an Re(2)(5+) core, Re(2)(mu-Cl)(3)Cl(2)(PMe(3))(4) (2), and a triply bonded Re(II) compound, 1,2,7,8-Re(2)Cl(4)(PMe(3))(4) (3), respectively. Two-electron reduction of 1 in the presence of tetrabutylammonium chloride affords a new triply bonded complex of the Re(2)(4+) core, [Bu(n)()(4)N][1,2,7-Re(2)Cl(5)(PMe(3))(3)] (4). Oxidation of 1 with NOBF(4) yields a Re(IV) mononuclear compound, trans-ReCl(4)(PMe(3))(2) (5). Two isomers of the monomeric Re(III) anion, [ReCl(4)(PMe(3))(2)](-) (6, 7), have been isolated as side products. The crystal structures of compounds 2 and 4-7 have been determined by X-ray crystallography. The Re-Re distance in the face-sharing complex 2 of 2.686(1) A is relatively short. The metal-metal bond length in anion 4 of 2.2354(7) A is consistent with the usual values for the triply bonded Re(2)(4+) core compounds. In addition, a cis arrangement of trimethylphosphine ligands in the starting material 1 is retained upon reduction in the dinuclear products 2-4.

Neutral dodecanuclear supramolecular complexes containing dimetal units linked by the trimesate anion.

Two compounds having six metal-metal bonded Mo(2)(4+) and Rh(2)(4+) units, the midpoints of which occupy the vertexes of an octahedron, are described here. Each of the M(2)(4+) units is also bridged by two mutually cis formamidinate groups of the type DAniF = N,N'-di-p-anisylformamidinate. These units are linked to each other by four tricarboxylate anions from trimesic acid, the centers of which form a tetrahedron that is encapsulated by the octahedron of dimetal units. Each of the neutral cages has a clathrated solvent molecule, CH(2)Cl(2) when the metal M is Mo and CH(3)CN when it is Rh. For the latter, there are CH(3)CN molecules occupying (2)/(3) of the axial sites on the Rh(2) units in a way that reduces the symmetry. These symmetrical structures appear to persist in solution as shown by the (1)H NMR spectra. The compounds [M(2)(cis-DAniF)(2)](6)[1,3,5-C(6)H(3)(CO(2))(3)](4), 1 for M = Mo and 2 for M = Rh, were crystallized as 1.22.1CH(3)CN.2.3CH(2)Cl(2) and 2.13.9CH(3)CN, respectively. In 1 there are four crystallographically independent quadruply bonded Mo-Mo distances in the narrow range 2.098-2.104 A. For 2, the six independent singly bonded Rh-Rh distances are in the range 2.428-2.438 A.

Using structures formed by dirhodium tetra(trifluoroacetate) with polycyclic aromatic hydrocarbons to prospect for maximum pi-electron density: Hückel calculations get it right.

A new class of supramolecular assemblies derived from a powerful Lewis acid in the form of dirhodium(II) tetra(trifluoroacetate) and various planar polycyclic aromatic hydrocarbons (PAHs) as donors has been prepared using a solventless technique. As a result, a number of novel adducts [Rh2(O2CCF3)4]x(L)y with various stoichiometries, x:y = 1:2, 1:1, 3:2, and 3:1, have been isolated in crystalline form. The following PAHs have been employed: acenaphthylene C12H8 (L1); acenaphthene C12H10 (L2); anthracene (L3) and phenanthrene (L4), C14H10; pyrene (L5) and fluoranthene (L6), C16H10; a series of isomers of the C18H12 composition: 1,2-benzanthracene (L7), triphenylene (L8), and chrysene (L9). Single-crystal X-ray diffraction studies have revealed a variety of structural motifs ranging from discrete molecules to extended 1D chains and 2D networks. In the bis-adducts, [Rh2(O2CCF3)4](L)2, an aromatic ligand is axially coordinated to the rhodium atoms through two long inequivalent Rh-C linkages at each end of the dirhodium complex. In the 1D complexes ([Rh2(O2CCF3)4](L))infinity aromatic ligands serve as bidentate links between two dirhodium units, while in 2D structures PAHs act as polydentate linkers, each coordinated to several rhodium atoms. Each linkage of a PAH consisted of an off-centered eta(2) coordination toward a single rhodium center. Simple Hückel calculations performed on the PAHs were used to calculate pi-electron densities for the C-C bonds, and these densities were compared to the experimental results.

Controlling the dimensionality of metal-metal bonded Rrh(2)(4+) polymers by the length of the linker. A disciplined example of crystal engineering.

Reaction of the molecular loop [Rh(2)(cis-DAniF)(2)(CH(3)CN)](2)(malonato)(2), DAniF = N,N'-di-p-anisylformamidinate, with 2 equiv of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-biphenyldinitrile gives a linear tubular structure with Rh-Rh distances of 2.435(1) A. A comparison of the structures obtained with this molecular loop but employing other linkers support the idea that longer linkers favor one-dimensional structures while shorter linkers favor two-dimensional structures because of the increased clashing between the large p-anisyl groups. Crystallographic data at 213(2) K for [[Rh(2)(cis-DAniF)(2)](2)(O(2)CCH(2)CO(2))(2)(NCC(6)F(4)C(6)F(4)CN)(2)] x 6.8nCH(2)Cl(2) are: monoclinic, P2(1)/m, a = 11.802(1), b = 28.303(2), c = 18.820(2) A, beta = 95.673(2) degrees, and Z = 2.

Supramolecular arrays based on dimetal building units.

Supramolecular chemistry is today a major thrust area, a significant part of which is based on the use of metal atoms or ions as key elements in promoting the assembly of and dictating the main structural features of the supramolecular products. Most of the work has been done with single metal atoms or ions in this role, but considerable success has already been achieved by employing M-M bonded dimetal entities instead. We review here the work done in our laboratory. Metal-metal bonded cationic complexes of the [M(2)(DAniF)(n)(MeCN)(8-2n)]((4-n)+) type, where M = Mo or Rh and DAniF is an N,N'-di-p-anisylformamidinate anion, have been used as subunit precursors and then linked by various equatorial and axial bridging groups such as polycarboxylate anions, polypyridyls, and polynitriles. Characterization of the products by single-crystal X-ray diffraction, CV, DPV, NMR, and other spectroscopic techniques has revealed the presence of discrete tetranuclear (pairs or loops), hexanuclear (triangles), octanuclear (squares), and dodecanuclear (cages) species and one-, two-, or three-dimensional molecular nanotubes. These compounds display a rich electrochemical behavior which is affected by the nature of the linkers.

Correlation of structure and triboluminescence for tetrahedral manganese(II) compounds.

To investigate the structural basis of triboluminescence, several known tetrahedrally coordinated Mn(II) complexes have been synthesized according to literature methods and their crystal structures have been determined by X-ray diffraction. Among them, (MePh(3)P)(2)[MnCl(4)] (2), a = 15.4804(4) A, cubic, space group P2(1)3, Z = 4; (Et(4)N)(2)[MnBr(4)] (4), a = 13.362(1) A, c = 14.411(1) A, tetragonal, space group P42(1)m, Z = 4; MnBr(2)(OPPh(3))(2) (7), a = 9.974(1) A, b = 10.191(3) A, c = 10.538(2) A, alpha = 65.32(1) degrees, beta = 63.49(1) degrees, gamma = 89.44(2) degrees, triclinic, space group P1, Z = 1; and MnBr(2)(OAsPh(3))(2) (10), a = 17.816(3) A, b = 10.164(1) A, c = 18.807(3) A, orthorhombic, space group Pca2(1), Z = 4 were reported to be triboluminescent and (Me(4)N)(2)[MnCl(4)] (3), a = 9.016(3) A, b = 36.90(2) A, c = 15.495(3) A, beta = 90.72(3) degrees, monoclinic, space group P2(1)/n, Z = 12, and MnI(2)(OAsPh(3))(2) (11), a = 10.094(4) A, b = 10.439(2) A, c = 34.852(2) A, alpha = 83.17(4) degrees, beta = 86.09(2) degrees, gamma = 75.16(3) degrees, triclinic, space group P1, Z = 4, were reported to be not triboluminescent. The result supports the correlation between space group acentricity and triboluminescence activity.

Quadridentate bridging EO(4)(2-) (E = S, Mo, W) ligands and their role as electronic bridges.

Three compounds containing two quadruply bonded Mo(2)(DAniF)(3) (DAniF = N,N'-di-p-anisylformamidinate) units linked by tetrahedral EO(4)(2-) anions (E = S, Mo, W) have been prepared and characterized by crystallography and NMR. The linkers in these [Mo(2)(DAniF)(3)](2)(mu-EO(4)) compounds hold the Mo(2) units in an approximately perpendicular orientation and mediate strong electrochemical communication between them. Each of the three compounds shows two quasireversible (mu-SO(4)) or fully reversible (mu-MoO(4), mu-WO(4)) features in its cyclic voltammogram corresponding to successive oxidation of each of its Mo(2) units. The DeltaE(1/2) values are the largest thus far measured for Mo(2)-X-Mo(2) bridged complexes and may be sufficiently large to permit isolation of the singly oxidized species.

Di- and trinuclear complexes with the mono- and dianion of 2,6-bis(phenylamino)pyridine: high-field displacement of chemical shifts due to the magnetic anisotropy of quadruple bonds.

The monoanion of 2,6-bis(phenylamino)pyridine (HBPAP(-)) has been found to support quadruply bonded Cr(2)(4+) and Mo(2)(4+) units in Cr(2)(HBPAP)(4) (1) and Mo(2)(HBPAP)(4) (2). The corresponding dianion BPAP(2)(-) was able to stabilize the trinuclear complexes, (TBA)(2)Cr(3)(BPAP)(4) (3) and (TBA)(2)Ni(3)(BPAP)(4) (4), where TBA is the tetrabutylammonium cation. The dinuclear complexes have the typical paddlewheel configuration with Cr-Cr distances of about 1.87 A and a Mo-Mo distance of 2.0813(5) A and exhibit a high-field displacement of the corresponding N-H signals caused by the magnetic anisotropy of the quadruple bonds. For the trinuclear complexes, 3 has a linear chain of three chromium atoms arranged in an unsymmetrical fashion with two chromium atoms paired to give a quadruply bonded unit (Cr-Cr distance: 1.904(3) A) and an isolated, square planar Cr(II) unit at 2.589(3) A from the dimetal unit. On the other hand, the three nickel atoms in 4 are evenly spaced, having Ni.Ni distances of 2.3682(8) A. The trinuclear compounds show a twisted conformation with an overall torsion angle of about 30 degrees.

The simplest supramolecular complexes containing pairs of Mo(2)(formamidinate)(3) units linked with various dicarboxylates: preparative methods, structures, and electrochemistry.

Twelve compounds containing two quadruply bonded Mo(2)(DAniF)(3) (DAniF = N,N'-di-p-anisylformamidinate) units linked by dicarboxylate anions have been prepared in high purity and good yields. All of these compounds have been characterized by crystallography and NMR. The dinuclear pairs display electrochemical behavior which is controlled by the nature of the bridging dicarboxylate group. As described by the linkers, the compounds are oxalate, 1; acetylene dicarboxylate, 2; fumarate, 3; tetrafluorophthalate, 4; carborane dicarboxylate, 5; ferrocene dicarboxylate, 6; malonate, 7; succinate, 8; propane-1,3-dicarboxylate, 9; tetrafluorosuccinate, 10; bicyclo[1.1.1]pentane-1,3-dicarboxylate, 11; and trans-1,4-cyclohexanedicarboxylate, 12.

Tuning the metal-metal bonds in the linear tricobalt compound Co3(dpa)(4)Cl2: bond-stretch and spin-state isomers.

Sixteen crystal structures have been determined for the Co3(dpa)(4)Cl2 (1) molecule in the following five crystalline solvates: 1.0.85(C2H5)(2)O.0.15CH2Cl2 (at 120, 213, 296 K); 1.C(4)H(8)O (at 120, 295 K); 1.C(6)H(6) (at 170, 213, 260, 316 K); 1.C(6)H(12) (at 120, 213, 295 K); and 1.1.75C(7)H(8).0.5C(6)H(14) (at 90, 110, 170, 298 K). For 1.0.85(C(2)H(5))(2)O.0.15CH2Cl2 the molecule of 1 is almost symmetrical at 120 K (Co-Co distances of 2.3191(3) and 2.3304(3) A) and remains so at 296 K (2.2320(3) and 2.3667(4) A). For 1.C(4)H(8)O the Co(3) chain is precisely symmetric at both 120 and 295 K though the Co-Co distances increase from 2.3111(4) to 2.3484(4) A as the temperature rises. Compound 1.C(6)H(6) is isomorphous with 1.C(4)H(8)O at 213 and 295 K and has rigorously symmetrical molecules at these two temperatures. Between 213 and 120 K the space group changes from Pccn to P2(1)/c, so that a symmetrical arrangement is no longer required and the two Co-Co distances then differ slightly (by 0.013 A). For 1.C(6)H(6) there is a phase change between 316 K (Pca2(1)) and 260 K (Pna2(1)). At all four temperatures, however, the molecule is almost symmetrical, with the two independent Co-Co distances never differing by more than 0.026 A. 1.1.75C(7)H(8).0.5C(6)H(14) contains, at all temperatures between 90 and 298 K, two crystallographically independent molecules, each of which is distinctly unsymmetrical at 298 K (Co-Co distances of 2.312(2) and 2.442(2) A for one and 2.310(2) and 2.471(2) for the other). In the first of these the distances converge to a much smaller separation (0.056 A) at 90 K while in the second the difference decreases to only 0.006 A at 90 K. Magnetic susceptibility measurements from 1.8 to 350 K indicate in each case that a gradual spin crossover, from a doublet to a quartet state, occurs over this temperature range.

Compounds with symmetrical tricobalt chains wrapped by dipyridylamide ligands and cyanide or isothiocyanate ions as terminal ligands.

Three new linear compounds of the type Co(3)(dpa)(4)X(2), where dpa is the anion of di(2-pyridyl)amine and X is NCS(-) (5), CN(-) (6), and N(CN)(2)(-) (7), have been prepared, and their structures and magnetic behavior have been studied. In all of them, including three different solvates of 5, the Co(3) chains are symmetrical with Co-Co distances of ca. 2.31-2.32 A. The appearance of four lines in the (1)H NMR spectra of the three compounds is also consistent with a symmetrical structure in solution. For all compounds, the magnetic behavior is quite similar with mu(eff) of ca. 1.9-2.0 micro(B) at temperatures between 1.8 and 200 K. As the temperature increases, the effective moments increase gradually, but since saturation is not reached, even at 400 K, the high-spin state cannot be assigned.

Dinuclear and heteropolynuclear complexes containing Mo2(4+) units.

The quadruply bonded compound Mo2(DpyF)4 (1), where DpyF- is the anion of N,N'-di(2-pyridyl)formamidine, has been prepared by ligand substitution reactions of Mo2(OOCCF3)4 and either the neutral ligand, HDpyF, at ambient temperature or its lithium salt, LiDpyF, under refluxing conditions. An X-ray structural analysis shows that 1 has a paddlewheel structure with a [symbol: see text] distance of 2.1108(6) A. Reaction of 1 with CoCl2 in methanol produces the paramagnetic compound [Mo2Co(DpyF)4][CoCl4].2MeOH (2). The Co(II) atom in the cation [Mo2Co(DpyF)4]2+ resides on a low-spin hexacoordinate environment (S = 1/2) with a Co...Mo separation of 2.979(6) A, suggesting there is no direct bonding interaction between the Co and Mo atoms. The Mo-Mo distance of 2.1096(5) A is similar to that in 1. Reaction of 1 and CuCl in methanol yields [Mo2Cu4(DpyF)4Cl2][CuCl2]2.2MeOHxEt2O (3). In the cation there are two copper atoms on each side of the Mo2 core. Each is coordinated to two pyridyl nitrogen atoms of the cis DpyF- ligands and loosely bridged to the other by a chloride ion. As a result, the Cu(I) atoms are not aligned with the Mo2 unit. The Cu to Mo separations are in the range 3.003(1)-3.015(1) A, and the Mo-Mo distance of 2.127(1) A is comparable to those in 1 and 2.

Connecting pairs of dimetal units to form molecular loops.

Four compounds consisting of molecular loops formed from two quadruply bonded Mo2(DAniF)2 (DAniF = N,N'-di-p-anisylformamidinate) units linked by two dicarboxylate anions have been prepared in high purity and essentially quantitative yields. These compounds have been characterized by crystallography and NMR spectroscopy and display electrochemical behavior dependent on the nature of the dicarboxylate anion. However, the electronic communication between the two Mo2(4+) units is not strong. As denoted by the dicarboxylate linkers, the compounds are malonate, 1, 1,4-phenylendiacetate, 2, homophthalate, 3, and trans-cyclopentane-1,2-dicarboxylate, 4.

Supramolecular squares with Mo2(4+) corners.

Seven complexes obtained by reacting the quadruply bonded complex [Mo2(cis-DAniF)2(CH3CN)4](BF4)2 (DAniF = N,N'-di-p-anisylformamidinate) and (Bun4N+)2(Carb2-), where Carb2- is a dicarboxylate anion, have been found to have a ratio of dimetal unit to dicarboxylate of 1:1. As noted by the carboxylate linker, the compounds are oxalate, 1, fumarate, 2, ferrocene dicarboxylate, 3, 4,4'-biphenyldicarboxylate, 4, acetylenedicarboxylate, 5, tetrafluorophthalate, 6, and carborane dicarboxylate, 7. Structural characterization of 1-4 revealed a square of dimolybdenum units linked by the dicarboxylate anions, each having an interstice capable of accommodating specific solvent molecules. Results of NMR studies of all seven compounds are consistent with the presence of a highly symmetrical structure. These compounds display a rich electrochemical behavior that is affected by the nature of the carboxylate group.