Electronic Structure of [Pt(2)(&mgr;-O(2)CCH(3))(4)(H(2)O)(2)](2+) Using the Quasi-Relativistic Xalpha-SW Method: Analysis of Metal-Metal Bonding, Assignment of Electronic Spectra, and Comparison with Rh(2)(&mgr;-O(2)CCH(3))(4)(H(2)O)(2)

The electronic structure and metal-metal bonding in the classic d(7)d(7) tetra-bridged lantern dimer [Pt(2)(O(2)CCH(3))(4)(H(2)O)(2)](2+) has been investigated by performing quasi-relativistic Xalpha-SW molecular orbital calculations on the analogous formate-bridged complex. From the calculations, the highest occupied and lowest unoccupied metal-based levels are delta(Pt(2)) and sigma(Pt(2)), respectively, indicating a metal-metal single bond analogous to the isoelectronic Rh(II) complex. The energetic ordering of the main metal-metal bonding levels is, however, quite different from that found for the Rh(II) complex, and the upper metal-metal bonding and antibonding levels have significantly more ligand character. As found for the related complex [W(2)(O(2)CH)(4)], the inclusion of relativistic effects leads to a further strengthening of the metal-metal sigma bond as a result of the increased involvement of the higher-lying platinum 6s orbital. The low-temperature absorption spectrum of [Pt(2)(O(2)CCH(3))(4)(H(2)O)(2)](2+) is assigned on the basis of Xalpha-SW calculated transition energies and oscillator strengths. Unlike the analogous Rh(II) spectrum, the visible and near-UV absorption spectrum is dominated by charge transfer (CT) transitions. The weak, visible bands at 27 500 and 31 500 cm(-)(1) are assigned to Ow --> sigma(Pt(2)) and OAc --> sigma(Pt(2)) CT transitions, respectively, although the donor orbital in the latter transition has around 25% pi(Pt(2)) character. The intense near-UV band around 37 500 cm(-)(1) displays the typical lower energy shift as the axial substituents are changed from H(2)O to Cl and Br, indicative of significant charge transfer character. From the calculated oscillator strengths, a number of transitions, mostly OAc --> sigma(Pt-O) CT in nature, are predicted to contribute to this band, including the metal-based sigma(Pt(2)) --> sigma(Pt(2)) transition. The close similarity in the absorption spectra of the CH(3)COO(-), SO(4)(2)(-), and HPO(4)(2)(-) bridged Pt(III) complexes suggests that analogous spectral assignments should apply to [Pt(2)(SO(4))(4)(H(2)O)(2)](2)(-) and [Pt(2)(HPO(4))(4)(H(2)O)(2)](2)(-). Consequently, the anomalous MCD spectra reported recently for the intense near-UV band in the SO(4)(2)(-) and HPO(4)(2)(-) bridged Pt(III) complexes can be rationalized on the basis of contributions from either SO(4) --> sigma(Pt-O) or HPO(4) --> sigma(Pt-O) CT transitions. The electronic absorption spectrum of [Rh(2)(O(2)CCH(3))(4)(H(2)O)(2)] has been re-examined on the basis of Xalpha-SW calculated transition energies and oscillator strengths. The intense UV band at approximately 45 000 cm(-)(1) is predicted to arise from several excitations, both metal-centered and CT in origin. The lower energy shoulder at approximately 40 000 cm(-)(1) is largely attributed to the metal-based sigma(Rh(2)) --> sigma(Rh(2)) transition.     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.     

Magnetic Susceptibility Trends in Oxo-Bridged, Dinuclear Chromium(III) Complexes. Crystal Structure of [(tmpa)Cr(&mgr;-O)(&mgr;-CO(3))Cr(tmpa)](ClO(4))(2).2H(2)O

The synthesis and physical characterization of oxo-bridged [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) complexes (tmpa = tris(2-pyridylmethyl)amine) containing a variety of complementary ligands (X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-)) are described, with the objective of understanding factors underlying variations in the antiferromagnetic coupling constant J. We also present the crystal structure of [(tmpa)Cr(&mgr;-O)(&mgr;-CO(3))Cr(tmpa)](ClO(4))(2).2H(2)O, for comparison with previous findings on [(tmpa)Cr(&mgr;-O)(&mgr;-CH(3)CO(2))Cr(tmpa)](ClO(4))(3). The carbonate-bridged complex crystallizes in the monoclinic space group P2(1)/c with a = 11.286(10) ?, b = 18.12(2) ?, c = 20.592(12) ?, beta = 95.99(5) degrees, and V = 4190 ?(3) and Z = 4. Asymmetric tmpa ligation pertains, with apical N atoms situated trans to bridging oxo and acido O atoms. Key structural parameters include Cr-O(b) bond lengths of 1.818(6) and 1.838(6) ?, Cr-OCO(2) distances of 1.924(7) and 1.934(7) ?, and a bridging bond angle of 128.3(3) degrees. Several attempts to prepare oxo, amido-bridged dimers were unsuccessful, but the nearlinear [Cr(tmpa)(N(CN)(2))](2)O(ClO(4))(2).3H(2)O complex was isolated from the reaction of dicyanamide ion with [Cr(tmpa)(OH)](2)(4+). In contrast to the behavior of analogous diiron(III) complexes, antiferromagnetic coupling constants of [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) dinuclear species are highly responsive to the X group. Considering the complexes with X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-), SO(4)(2)(-), and RCO(2)(-) (10 R substituents), we find a reasonably linear, empirical relationship between J and oxo bridge basicity, as measured by pK(a) (Cr(OH)Cr) values in aqueous solution. While there is no theoretical basis for such a correlation between solid-state and solution-phase properties, this relationship demonstrates that CrOCr pi-bonding contributes significantly to antiferromagnetic exchange. Thus, J tends to become less negative with increasing &mgr;-O(2)(-) basicity, showing that greater availability of a bridging oxo group lone pair toward the proton, with decreasing CrOCr pi-interaction, reduces the singlet-triplet gap.     

Coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) and (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2): the effect of alkylating the nitrogen bridge on ligand bridging versus chelating behavior

The coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(R)P(C(6)H(5))(2) [R = H (dppa); R = CH(3) (dppma)] has been investigated by (31)P NMR and electrospray mass spectrometry (ESMS). Species observed by (31)P NMR include Ag(2)(mu-dppa)(2+), Ag(2)(mu-dppa)(2)(2+), Ag(2)(mu-dppa)(3)(2+), Ag(2)(mu-dppma)(2+), Ag(2)(mu-dppma)(2)(2+), and Ag(eta(2)-dppma)(2)(+). Species observed by ESMS at low cone voltages were Ag(2)(dppa)(2)(2+), Ag(2)(dppa)(3)(2+), Ag(2)(dppma)(2)(2+), and Ag(dppma)(2)(+). (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2) showed a strong tendency to chelate, while (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) preferred to bridge. Differences in the bridging versus chelating behavior of the ligands are assigned to the Thorpe-Ingold effect, where the methyl group on nitrogen sterically interacts with the phenyl groups on phosphorus. The crystal structure of the three-coordinate dinuclear silver(I) complex (Ag(2)[(C(6)H(5))(2)PN(H)P(C(6)H(5))(2)](3))(BF(4))(2) has been determined. Bond distances include Ag-Ag = 2.812(1) A, Ag(1)-P(av) = 2.492(3) A, and Ag(2)-P(av) = 2.509(3) A. The compound crystallizes in the monoclinic space group Cc at 294 K, with a = 18.102(4)(o), Z = 4, V = 7261(3) A(3), R = 0.0503, and R(W) = 0.0670.     

Reaction of bis(phosphine)(hydrotris(3,5-dimethylpyrazolyl)borato)rhodium(I) with phenylacetylene,p-nitrobenzaldehyde,and triphenyltin hydride: structures of [Rh(Tp)(PPh(3))(2)], [Rh(Tp)(H)(C(2)Ph)(P(4-C(6)H(4)F)(3))], [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PPh(3))], and [Rh(Tp)(H)(SnPh(3))(PPh(3))

The complexes [Rh(Tp)(PPh(3))(2)] (1a) and [Rh(Tp)(P(4-C(6)H(4)F)(3))(2)] (1b) combine with PhC(2)H, 4-NO(2)-C(6)H(4)CHO and Ph(3)SnH to give [Rh(Tp)(H)(C(2)Ph)(PR(3))] (R = Ph, 2a; R = 4-C(6)H(4)F, 2b), [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PR(3))] (R = Ph, 3a), and [Rh(Tp)(H)(SnPh(3))(PR(3))] (R = Ph, 4a; R = 4-C(6)H(4)F, 4b) in moderate to good yield. Complexes 1a, 2b, 3a, and 4a have been structurally characterized. In 1a the Tp ligand is bidentate, in 2b, 3a, and 4a it is tridentate. Crystal data for 1a: space group P2(1)/c; a = 11.9664(19), b = 21.355(3), c = 20.685(3) A; beta = 112.576(7) degrees; V = 4880.8(12) A(3); Z = 4; R = 0.0441. Data for 2b: space group P(-)1; a = 10.130(3), b = 12.869(4), c = 17.038(5) A; alpha = 78.641(6), beta = 76.040(5), gamma = 81.210(6) degrees; V = 2100.3(11) A(3); Z = 2; R = 0.0493. Data for 3a: space group P(-)1; a = 10.0073(11), b = 10.5116(12), c = 19.874(2) A; alpha = 83.728(2), beta = 88.759(2), gamma = 65.756(2) degrees; V =1894.2(4) A(3); Z = 2; R = 0.0253. Data for 4a: space group P2(1)/c; a = 15.545(2), b = 18.110(2), c = 17.810(2) A; beta = 95.094(3) degrees; V = 4994.1(10) A(3); Z = 4; R = 0.0256. NMR data ((1)H, (31)P, (103)Rh, (119)Sn) are also reported.     

Solid state and solution study of some phosphoramidate derivatives containing the P(O)NHC(O) bifunctional group: Crystal structures of CCl2HC(O)NHP(O)(NCH3(CH2C6H5))2, p-ClC6H4C(O)NHP(O)(NCH3(CH2C6H5))2, CCl2HC(O)NHP(O)(N(CH2C6H5)2)2 and p-BrC6H4C(O)NHP(O)(N(CH2C6H5)2)2

Synthetic methods for several novel phosphoramidate compounds containing the P(O)NHC(O) bifunctional group were developed. These compounds with the general formula R₁C(O)NHP(O)(N(R₂)(CH₂C₆H₅))₂, where R₁ = CCl₂H, p-ClC₆H₄, p-BrC₆H₄, o-FC₆H₄ and R₂ = hydrogen, methyl, benzyl, were characterized by several spectroscopic methods and analytical techniques. The effects of phosphorus substituents on the rotation rate around the P–N_amine bond were also investigated. ¹H NMR study of the synthesized compounds demonstrated that the presence of bulky groups attached to the phosphorus center and electron withdrawing groups in the amide moiety lead to large chemical-shift non-equivalence (Δδ_H) of diastereotopic methylene protons. The crystal structures of CCl₂HC(O)NHP(O)(NCH₃(CH₂C₆H₅))₂, p-ClC₆H₄C(O)NHP(O)(NCH₃(CH₂C₆H₅))₂, CCl₂HC(O)NHP(O)(N(CH₂C₆H₅)₂)₂ and p-BrC₆H₄C(O)NHP(O)(N(CH₂C₆H₅)₂)₂ were determined by X-ray crystallography using single crystals. The coordination around the phosphorus center in these compounds is best described as distorted tetrahedral and the P(O) and C(O) groups are anti with respect to each other. In the compound Br-C₆H₄C(O)NHP(O)(N(CH₂C₆H₅)₂)₂ (with two independent molecules in the unit cell), two conformers are connected to each other via two different N–H?O hydrogen bonds forming a non-centrosymmetric dimer. In the crystalline lattice of other compounds, the molecules form centrosymmetric dimers via pairs of same N–H?O hydrogen bonds. The structure of CCl₂HC(O)NHP(O)(N(CH₂C₆H₅)₂)₂ reveals an unusual intramolecular interaction between the oxygen of CO group and amine nitrogen.     

New rac‐XP(O)(OC6H5)(NHC6H4‐p‐CH3) [X = N(CH3)(cyclo‐C6H11) and NH(C3H5)] and rac‐(C6H5CH2NH)P(O)(OC6H5)(NH‐cyclo‐C6H11) mixed‐amide phosphinates

The mixed‐amide phosphinates, rac‐phenyl (N‐methylcyclohexylamido)(p‐tolylamido)phosphinate, C₂₀H₂₇N₂O₂P, (I), and rac‐phenyl (allylamido)(p‐tolylamido)phosphinate, C₁₆H₁₉N₂O₂P, (II), were synthesized from the racemic phosphorus–chlorine compound (R,S)‐(Cl)P(O)(OC₆H₅)(NHC₆H₄‐p‐CH₃). Furthermore, the phosphorus–chlorine compound ClP(O)(OC₆H₅)(NH‐cyclo‐C₆H₁₁) was synthesized for the first time and used for the synthesis of rac‐phenyl (benzylamido)(cyclohexylamido)phosphinate, C₁₉H₂₅N₂O₂P, (III). The strategies for the synthesis of racemic mixed‐amide phosphinates are discussed. The P atom in each compound is in a distorted tetrahedral (N¹)P(=O)(O)(N²) environment. In (I) and (II), the p‐tolylamido substituent makes a longer P—N bond than those involving the N‐methylcyclohexylamido and allylamido substituents. In (III), the differences between the P—N bond lengths involving the cyclohexylamido and benzylamido substituents are not significant. In all three structures, the phosphoryl O atom takes part with the N—H unit in hydrogen‐bonding interactions, viz. an N—H...O=P hydrogen bond for (I) and (N—H)(N—H)...O=P hydrogen bonds for (II) and (III), building linear arrangements along [001] for (I) and along [010] for (III), and a ladder arrangement along [100] for (II).     

Characterization and reactions of previously elusive 17-electron cations: electrochemical oxidations of (C(6)H(6))Cr(CO)(3) and (C(5)H(5))Co(CO)(2) in the presence of [B(C(6)F(5))(4)](-)

The electrochemical oxidations of (C6H6)Cr(CO)3, 1, and (C5H5)Co(CO)2, 2, when carried out in CH2Cl2/[NBu4][B(C6F5)4], allow the physical or chemical characterization of the 17-electron cations 1+ and 2+ at room temperature. The generation of 1+ on a synthetic time scale permits an electrochemical "switch" process involving facile substitution of CO by PPh3 as a route to (C6H6)Cr(CO)2PPh3. The radical 2+ undergoes a second-order reaction to give a product assigned as the metal-metal bonded dimer dication [Cp2Co2(CO)4]2+. The new anodic chemistry of these often-studied 18-electron compounds is made possible by increases in the solubility and thermal stability of the cation radicals in media containing the poorly nucleophilic anion [B(C6F5)4]-, TFAB.     

Nanoscale Hemispheres in Novel Mixed-Valent Uranyl Chromate(V,VI), (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6)

The structure of a novel mixed-valent chromium uranyl compound, (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6) (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 ?(2) and a height of about 8 ?. The hemispheres are centered by a UO(8) hexagonal bipyramid surrounded by six dimers of Cr(5+)O(5) square pyramids, UO(7) pentagonal bipyramids, and Cr(6+)O(4) tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U(21)Cr(23) and can be considered as derivatives of nanospherical cluster U(26)Cr(36) composed of three-, four-, and five-membered rings.     

2,6-Mes(2)C(6)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-) (Mes = 2,4,6-Me(3)C(6)H(2)): A compound containing a linear unsolvated two-coordinate gallium cation

The title compound [2,6-Mes(2)C(2)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-), 1, containing a linear two-coordinate gallium cation, has been obtained by metathesis reaction of [2,6-Mes(2)C(2)H(3)](2)GaCl with 2 equiv of Li[Al(OCH(CF(3))(2))(4)] in C(6)H(5)Cl solution at room temperature. Compound 1 has been characterized by (1)H, (13)C((1)H), (19)F, and (27)Al NMR spectroscopy and X-ray crystallography. Compound 1 consists of isolated [2,6-Mes(2)C(6)H(3)](2)Ga(+) cations and Li[Al(OCH(CF(3))(2))(4)](2)(-) anions. The C-Ga-C angle is 175.69(7) degrees, and the Ga-C distances are 1.9130(14) and 1.9145(16) A. The title compound is remarkably stable, is only a weak Lewis acid, and polymerizes cyclohexene oxide.     

Influence of Intramolecular Coordination on the Aggregation of Sodium Phenolate Complexes. X-ray Structures of [NaOC(6)H(4)(CH(2)NMe(2))-2](6) and [Na(OC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)(HOC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)](2)

The structural characterization of two new sodium phenolate complexes, containing ortho-amino substituents, enables the influence of intramolecular coordination on the aggregation of sodium phenolate complexes to be determined. Crystals of hexameric [NaOC(6)H(4)(CH(2)NMe(2))-2](6) (1a) are monoclinic, space group P2(1)/c, with a = 11.668(4) ?, b = 18.146(4) ?, c = 14.221(5) ?, beta = 110.76(3) ?, V = 2815.5(16) ?(3), and Z = 2; R = 0.0736 for 2051 reflections with I > 2.0sigma(I). Complex 1a contains a unique Na(6)O(6) core, consisting of two face-fused cubes, with the ortho-amino substituent of each phenolate coordinating to a sodium atom. In addition, two of the phenolate ligands have an eta(2)-arene interaction with an additional sodium atom in the core. Crystals of dimeric [(NaOC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)(HOC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)](2) (2b) are triclinic, space group P&onemacr;, with a = 10.0670(8) ?, b = 10.7121(7) ?, c = 27.131(3) ?, alpha = 92.176(8) degrees, beta = 99.928(8) degrees, gamma = 106.465(6) degrees, V = 2752.1(4) ?(3), and Z = 2; R = 0.0766 for 5329 reflections with I > 2.0sigma(I). Dimeric complex 2b contains two phenolate ligands, which bridge the two sodium atoms, each coordinating with one ortho-amino substituent to a sodium atom, while the second available ortho-amino substituent remains pendant. The coordination sphere of each sodium atom is completed by a (neutral) bidentate O,N-coordinated parent phenol molecule. The second ortho-amino substituent of this neutral phenol is involved in a hydrogen bridge with its acidic hydrogen. On the basis of these two new crystal structures and previously reported solid state structures for sodium phenolate complexes, it is shown that the introduction of first one and then two ortho-amino substituents into the phenolate ligands successively lowers the degree of association of these complexes in the solid state. In this process, the basic Na(2)O(2) building block of the molecular structures remains intact.     

A high-pressure iron K-edge x-ray absorption spectral study of the spin-state crossover in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2)

The room temperature iron K-edge X-ray absorption near edge structure spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) have been measured between ambient and 88 and 94 kbar, respectively, in an opposed diamond anvil cell. The iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2)undergoes the expected gradual spin-state crossover from the high-spin state to the low-spin state with increasing pressure. In contrast, the iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) remains high-spin between ambient and 78 kbar and is only transformed to the low-spin state at an applied pressure of between 78 and 94 kbar. No visible change is observed in the preedge peak in the spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) with increasing pressure, whereas the preedge peak in the spectra of ((e[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) changes as expected for a high-spin to low-spin crossover with increasing pressure. The difference in the spin-state crossover behavior of these two complexes is likely related to the unusual behavior of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) upon cooling.