Diamond‐ and Graphite‐Like Octacyanometalate‐Based Polymers Induced by Metal Ions

By using cyclohexane‐1,2‐diamine (chxn), Ni(ClO₄)₂ ? 6H₂O and Na₃[Mo(CN)₈] ? 4H₂O, a 3D diamond‐like polymer {[Ni^II(chxn)₂]₂[Mo^IV(CN)₈] ? 8H₂O}_n ( 1 ) was synthesised, whereas the reaction of chxn and Cu(ClO₄)₂ ? 6H₂O with Na₃[M^V(CN)₈] ? 4H₂O (M=Mo, W) afforded two isomorphous graphite‐like complexes {[Cu^II(chxn)₂]₃[Mo^V(CN)₈]₂ ? 2H₂O}_n ( 2 ) and {[Cu^II(chxn)₂]₃[W^V(CN)₈]₂ ? 2H₂O}_n ( 3 ). When the same synthetic procedure was employed, but replacing Na₃[Mo(CN)₈] ? 4H₂O by (Bu₃NH)₃[Mo(CN)₈] ? 4H₂O (Bu₃N=tributylamine), {[Cu^II(chxn)₂Mo^IV(CN)₈][Cu^II(chxn)₂] ? 2H₂O}_n ( 4 ) was obtained. Single‐crystal X‐ray diffraction analyses showed that the framework of 4 is similar to 2 and 3 , except that a discrete [Cu(chxn)₂]²⁺ moiety in 4 possesses large channels of parallel adjacent layers. The experimental results showed that in this system, the diamond‐ or graphite‐like framework was strongly influenced by the inducement of metal ions. The magnetic properties illustrate that the diamagnetic [Mo^IV(CN)₈] bridges mediate very weak antiferromagnetic coupling between the Ni^II ions in 1 , but lead to the paramagnetic behaviour in 4 because [Mo^IV(CN)₈] weakly coordinates to the Cu^II ions. The magnetic investigations of 2 and 3 indicate the presence of ferromagnetic coupling between the Cu^II and W^V/Mo^V ions, and the more diffuse 5d orbitals lead to a stronger magnetic coupling interaction between the W^V and Cu^II ions than between the Mo^V and Cu^II ions.     

Dianionic Mononuclear Cyclo‐P4 Complexes of Zero‐Valent Molybdenum: Coordination of the Cyclo‐P4 Dianion in the Absence of Intramolecular Charge Transfer

Relative to other cyclic poly‐phosphorus species (that is, cyclo‐P_n), the planar cyclo‐P₄ group is unique in its requirement of two additional electrons to achieve aromaticity. These electrons are supplied from one or more metal centers. However, the degree of charge transfer is dependent on the nature of the metal fragment. Unique examples of dianionic mononuclear η⁴‐P₄ complexes are presented that can be viewed as the simple coordination of the [cyclo‐P₄]^2? dianion to a neutral metal fragment. Treatment of the neutral, molybdenum cyclo‐P₄ complexes Mo(η⁴‐P₄)I₂(CO)(CNAr^Dipp2)₂ and Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)₂ with KC₈ produces the dianionic, three‐legged piano stool complexes, [Mo(η⁴‐P₄)(CO)(CNAr^Dipp2)₂]^2? and [Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)]^2?, respectively. Structural, spectroscopic, and computational studies reveal a similarity to the classic η⁶‐benzene complex (η⁶‐C₆H₆)Mo(CO)₃ regarding the metal‐center valence state and electronic population of the planar‐cyclic ligand π system.     

POM‐Catalyzed In Situ Ligand Synthesis for the Construction of Metal Complexes and Their Use in the Formation of Coordination Polymers

Six organic–inorganic hybrid materials were synthesized by the in situ oxidation of neocuproine by using MoO₃/Na₂MoO₄ as the catalyst in the presence of Cu(NO₃)₂. The crystal structures of Mo8‐Cu4‐PHEN and Mo8‐Cu2‐5(2PIC) are composed of [Mo₈O₂₆]^4? polyoxometalate (POM) units, whereas the crystal structure of Mo6‐Cu‐COPHEN is composed of a [Mo₆O₁₉]^2? POM unit; both POM units could be considered as the active form of the catalyst. Reaction of the hybrid materials with 1,3,5‐benzenetricarboxylic acid (BTC) resulted in the formation of two different coordination polymers (CPs) under different reaction conditions. These CPs, depending on their structural attributes, exhibit distinct differences in the adsorption of H₂, CO₂, and water. The use of 2‐methylpyridine instead of neocuproine does not give any oxidation products under the same reaction conditions due to the incorrect positioning of the methyl group with respect to the Cu^II center.     

Synthesis and structural characterization of a novel dimolybdenum(I) compound with mixed‐tribridging ligands: [Bu4N][Mo2(μ‐SPh)2(μ‐Cl(CO6]

A novel mixed‐tribridged dimolybdenum(I) compound [Bn₄N][Mo₂(μ‐SPh)₂(μ‐Cl)(CO)₆] (1) has been synthesized from the reaction of Mo₂(CO)₃(SPh)₂ with BU₄NCl. Compound 1 was characterized by IR, UV‐Vis and ¹H, ¹³C, ⁹⁵Mo NMR spectroscopic analyses. The electrochemical behavior was measured by cyclic voltammetry, indicating a quasi‐reversible two‐electron transfer in one step. The crystal structure determined by X‐ray crystallography shows that 1 contains a [Mo₂(μ‐S)₂(μ‐Cl)]^? core with a planar Mo₂S₂unit and a Cl bridge. The Mo? Mo distance is 0.28709(7) nm, and the Mo‐Cl‐Mo angle is 66.44(4)°. A newface‐sharing bioctahedral structure is discussed.     

Studies of molybdenum thiolato-complexes. The crystal and molecular structures of two triply bridged Mo(V) dimers, [Bu 4 n N][Mo2O2Cl5(SPh)2] and [Mo2O3(SPh)2(S2CNMe2)2]

Summary The complex [Bu ₄ ⁿ N][Mo₂O₂Cl₅(SPh)₂] has been prepared by reaction of [Bu ₄ ⁿ N][MoO(SPh)₄] with stoichiometric amounts of HCl and characterised by single crystal X-ray structure analysis. The dimer is bridged by two oxo-groups and one chloride and each Mo has pseudo-octahedral co-ordination. The related compound [Mo₂O₃(SPh)₂(S₂CNMe₂)₂] was synthesised by reaction of [MoO₂(S₂CNMe₂)₂] with thiophenol in methanol and has also been characterised crystallographically. In this case the triple-bridge consists of two thiophenolate sulphurs and one oxo-group, each molybdenum having pseudo-octahedral geometry. These structures are compared with other triply-bridged species.     

A novel two‐dimensional nickel(II) coordination polymer with 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene and azide ligands

The coordination geometry of the Ni^II atom in the title complex, poly[diazidobis[μ‐1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene‐κ²N⁴:N^4′]nickel(II)], [Ni(N₃)₂(C₁₂H₁₂N₆)₂]_n, is a distorted octahedron, in which the Ni^II atom lies on an inversion centre and is coordinated by four N atoms from the triazole rings of two symmetry‐related pairs of 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene (bbtz) ligands and two N atoms from two symmetry‐related monodentate azide ligands. The Ni^II atoms are bridged by four bbtz ligands to form a two‐dimensional (4,4)‐network.     

Molybdän‐ und Wolfram‐Komplexe mit MNS‐Sequenzen. Die Kristallstrukturen von [MoCl3(N3S2)(1,4‐Dioxan)2] und [Mo2Cl2(μ‐NSN)2(μ‐O)(NCMe3)(OCMe3)2]2

Molybdenum and Tungsten Complexes with MNS Sequences. Crystal Structures of [MoCl₃(N₃S₂)(1,4‐dioxane)₂] and [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ The cyclo‐thiazeno complexes [Cl₃MNSNSN]₂ of molybdenum and tungsten react with 1,4‐dioxane in dichloromethane suspension to give the binuclear donor‐acceptor complexes [μ‐(1,4‐dioxane){MCl₃(N₃S₂)}₂] which are characterized by IR spectroscopy. With excess 1,4‐dioxane the molybdenum compound forms the complex [MoCl₃(N₃S₂)(1,4‐dioxane)₂] in which, according to the crystal structure determination, one of the dioxane molecules coordinates at the molybdenum atom, the other one at one of the sulfur atoms of the cyclo‐thiazeno ring. The μ‐(NSN^2–) complex [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ has been obtained by the reaction of [MoN(OCMe₃)₃] with trithiazyle chloride in carbontetrachloride solution. According to the crystal structure determination this compound forms centrosymmetric dimeric molecules via two of the nitrogen atoms of two of the μ‐(NSN) groups to give a Mo₂N₂ fourmembered ring. [MoCl₃(N₃S₂)(1,4‐dioxane)₂]: Space group P2₁/c, Z = 4, lattice dimensions at –70 °C: a = 1522.9(2); b = 990.3(1); c = 1161.7(1) pm; β = 106.31(1)°, R₁ = 0.0317. [Mo₂Cl₂(μ‐NSN)₂(μ‐O)(NCMe₃)(OCMe₃)₂]₂ · 4 CCl₄: Space group P2₁/c, Z = 2, lattice dimensions at –83 °C: a = 1216.7(1); b = 2193.1(2); c = 1321.8(1) pm; β = 98.23(1)°; R₁ = 0.0507.     

The First Molybdenum Oxo‐iodide Cluster – [Mo4OI12]2–

Reaction of Mo(CO)₆ with Bu₄NI and I₂ in diglyme yielded a new butterfly Mo^III cluster [Mo₄OI₁₂]^2–. The structure of tetraphenylphosphonium salt was determined by X‐ray single crystal diffraction. Ph₄P⁺ and Bu₄N⁺ salts were further characterized by elemental analysis, mass spectrometry, energy‐dispersive X‐ray (EDX), IR, Raman, and UV/Vis spectroscopy and CVA studies. The cluster anion has a butterfly array of molybdenum atoms and can be represented as [Mo₄(μ₄‐O)(μ₃‐I)₂(μ₂‐I₄)I₆]^2–.     

[Mo2(O2C–CH3)4 · 1/2 {(CH2)6N4} · 1/2 CH2Cl2] – ein Donor‐Akzeptor‐Komplex mit supramolekularer Struktur

[Mo₂(O₂C–CH₃)₄ · ¹/₂ {(CH₂)₆N₄} · ¹/₂ CH₂Cl₂] – a Donor‐Acceptor Complex with Supramolecular Structure Yellow single crystals of [Mo₂(O₂C–CH₃)₄ · ¹/₂ {(CH₂)₆N₄} · ¹/₂ CH₂Cl₂] ( 1 ) have been obtained by the reaction of the silylated phosphaneimine Me₃SiNPEt₃ with [Mo₂(O₂C–CH₃)₄] in dichloromethane solution. 1 forms a three‐dimensional network with linear N–Mo:Mo–N and tetrahedral (CH₂)₆N₄Mo₄ moieties, which is topologically related with the PtS type. Space group P4₂/nnm, Z = 4, lattice dimensions at –70 °C: a = b = 1121.7(1), c = 1395.0(3) pm, R₁ = 0.0413.     

A novel two‐dimensional MnII coordination polymer with 1,2‐bis­(imidazol‐1‐yl)­ethane

In the crystal structure of the title complex, poly­[[di­azido­manganese(II)]‐di‐μ‐1,2‐bis­(imidazol‐1‐yl)­ethane‐κ⁴N³:N^3′], [Mn(N₃)₂(C₈H₁₀N₄)₂]_n or [Mn(N₃)₂(bim)₂]_n, where bim is 1,2‐­bis(imidazol‐1‐yl)­ethane, each Mn^II atom is six‐coordinated in a distorted octahedral coordination environment to four N atoms from four bim ligands and two N atoms from two azide ligands. The Mn^II atoms, which lie on inversion centres, are bridged by four bim ligands to form a two‐dimensional (4,4)‐network. The azide ligands are monodentate (terminal).     

A Facile Route for the Synthesis of Polycationic Tellurium Cluster Compounds: Synthesis in Ionic Liquid Media and Characterization by Single‐Crystal X‐ray Crystallography and Magnetic Susceptibility

An innovative soft chemical approach was applied, using ionic liquids as an alternative reaction medium for the synthesis of tellurium polycationic cluster compounds at room temperature. [Mo₂Te₁₂]I₆, Te₆[WOCl₄]₂, and Te₄[AlCl₄]₂ were isolated from the ionic liquid [BMIM]Cl/AlCl₃ ([BMIM]⁺: 1‐n‐butyl‐3‐methylimidazolium) and characterized. Black, cube‐shaped crystals of [Mo₂Te₁₂]I₆, which is not accessible by conventional chemical transport reaction, were obtained by reaction of the elements at room temperature in [BMIM]Cl/AlCl₃. The monoclinic structure (P2₁/n, a = 1138.92(2) pm, b = 1628.13(2) pm, c = 1611.05(2) pm, β = 105.88(1) °) is homeotypic to the triclinic bromide [Mo₂Te₁₂]Br₆. In the binulear complex [Mo₂Te₁₂]⁶⁺, the molybdenum(III) atoms are η⁴‐coordinated by terminal Te₄²⁺ rings and two bridging η²‐Te₂^2– dumbbells. Despite the short Mo···Mo distance of 297.16(5) pm, coupling of the magnetic moments is not observed. The paramagnetic moment of 3.53 μ_B per molybdenum(III) atom corresponds to an electron count of seventeen. Black crystals of monoclinic Te₆[WOCl₄]₂ are obtained by the oxidation of tellurium with WOCl₄ in [BMIM]Cl/AlCl₃. Tellurium and tellurium(IV) synproportionate in the ionic liquid at room temperature yielding violet crystals of orthorhombic Te₄[AlCl₄]₂.     

Oxidative Reactions of the MoIV Dialkyl Complex [{(3‐CF3C6H4NCH2CH2)2NMe}Mo(CH2SiMe3)2]

The structure of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] (in which (CF₃N₂NMe)^2? is [(3‐CF₃C₆H₄NCH₂CH₂)₂NMe]^2?) is approximately trigonal bipyramidal with one axial and one equatorial alkyl ligand. Heating of solutions of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] in [D₆]benzene in the presence of five equivalents of 2‐butyne led to diamagnetic [(CF₃N₂NMe)Mo(CHSiMe₃)(η²‐MeC?CMe)], whose structure is approximately square pyramidal with the alkyne occupying the axial site. Addition of one equivalent of cyclohexene sulfide to [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] at room temperature produced the diamagnetic, dimeric molybdenum(IV) sulfido complex, [{(CF₃N₂NMe)MoS}₂]. This complex is composed of two approximately trigonal bipyramidal centers, each containing one axial and one equatorial sulfur atom. Oxidation of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] with hexachloroethane resulted in formation of tetramethylsilane, HCl, and the sparingly soluble, red alkylidyne complex, [{(CF₃N₂NMe)Mo(CSiMe₃)Cl}₂]. This complex forms a dimer through bridging chlorides. The oxidation reactions of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] with 2‐butyne, cyclohexene sulfide, or C₂Cl₆ are all proposed to proceed by α‐hydrogen abstraction in the Mo^VI species to yield (initially) the Mo?CHSiMe₃ species and tetramethylsilane.     

The Molybdenum(V) and Tungsten(VI) Oxoazides [MoO(N3)3], [MoO(N3)3⋅2 CH3CN], [(bipy)MoO(N3)3], [MoO(N3)5]2−, [WO(N3)4], and [WO(N3)4⋅CH3CN]

A series of novel molybdenum(V) and tungsten(VI) oxoazides was prepared starting from [MOF₄] (M=Mo, W) and Me₃SiN₃. While [WO(N₃)₄] was formed through fluoride–azide exchange in the reaction of Me₃SiN₃ with WOF₄ in SO₂ solution, the reaction with MoOF₄ resulted in a reduction of Mo^VI to Mo^V and formation of [MoO(N₃)₃]. Carried out in acetonitrile solution, these reactions resulted in the isolation of the corresponding adducts [MoO(N₃)₃?2 CH₃CN] and [WO(N₃)₄?CH₃CN]. Subsequent reactions of [MoO(N₃)₃] with 2,2′‐bipyridine and [PPh₄][N₃] resulted in the formation and isolation of [(bipy)MoO(N₃)₃] and [PPh₄]₂[MoO(N₃)₅], respectively. Most molybdenum(V) and tungsten(VI) oxoazides were fully characterized by their vibrational spectra, impact, friction and thermal sensitivity data and, in the case of [WO(N₃)₄?CH₃CN], [(bipy)MoO(N₃)₃], and [PPh₄]₂[MoO(N₃)₅], by their X‐ray crystal structures.     

Neue Phosphaniminato‐Komplexe von Molybdän und Wolfram. Die Kristallstrukturen von [(μ‐S2N2){MoCl4(NPPh3)}2], [Mo(NPPh3)4][BF4]2, [W(S)2(NPPh3)2] und [Ph3PNH2]+[SCN]–

New Phosphoraneiminato Complexes of Molybdenum and Tungsten. Crystal Structures of [(μ‐S₂N₂){MoCl₄(NPPh₃)}₂], [Mo(NPPh₃)₄][BF₄]₂, [W(S)₂(NPPh₃)₂], and [Ph₃PNH₂]⁺[SCN]^– The binuclear molybdenum(V)phosphoraneiminato complex [(μ‐S₂N₂){Mo^VCl₄(NPPh₃)}₂] ( 1 ) has been prepared by the reaction of the chlorothionitreno complex [Mo^VICl₄(NSCl)]₂ with Me₃SiNPPh₃ in dichloromethane forming green crystals. The temperature dependent magnetic susceptibility in the range of 2–30 K shows ideal behaviour according to the Curie law with a magnetic moment of 1.60 B.M. According to the crystal structure determination 1 forms centrosymmetric molecules in which the molybdenum atoms are connected by the nitrogen atoms of the S₂N₂ molecule. In trans‐position to it the nitrogen atoms of the phosphoraneiminato groups (NPPh₃^–) are coordinated with Mo–N bond lengths of 171(1) pm. The tetrakis(phosphoraneiminato) complex [Mo(NPPh₃)₄]‐ [BF₄]₂ ( 2 ) has been obtained as colourless crystal needles by the reaction of MoN(NPPh₃)₃ with boron trifluoride etherate in toluene solution. In the dication the molybdenum atom is tetrahedrally coordinated by the nitrogen atoms of the (NPPh₃^–) groups with Mo–N bond lengths of 179,8–181,0(3) pm. The dithio‐bis(phosphoraneiminato) tungsten complex [W(S)₂(NPPh₃)₂] ( 3 ) is formed as yellow crystals as well as [Ph₃PNH₂]⁺[SCN]^– ( 4 ) from the reaction of WN(NPPh₃)₃ with carbon disulfide in tetrahydrofurane in the presence of traces of water. 3 has a monomeric molecular structure with tetrahedrally coordinated tungsten atom with bond lengths W–S of 214.5(5) pm and W–N of 179(1) pm. In the structure of 4 the thiocyanate ions are associated by hydrogen bonds of the NH₂ group of the [Ph₃PNH₂]⁺ ion to give a zigzag chain. 1 : Space group Pbca, Z = 4, lattice constants at –80 °C: a = 1647.9(3), b = 1460.8(2), c = 1810.4(4) pm; R₁ = 0.0981. 2 : Space group P1, Z = 2, lattice constants at –80 °C: a = 1162.5(1), b = 1238.0(1), c = 2346.2(2) pm; α = 103.14(1)°, β = 90.13(1)°, γ = 97.66(1)°; R₁ = 0.0423. 3 : Space group Fdd2, Z = 8, lattice constants at –80 °C: a = 3310.1(4), b = 2059.7(2), c = 966,7(1) pm; R₁ = 0.0696. 4 : Space group P2₁2₁2₁, Z = 4, lattice constants at –80 °C: a = 1118.4(1), b = 1206.7(1), c = 1279.9(1) pm; R₁ = 0.0311.     

A three‐dimensional hybrid framework based on novel [Co4Mo4] bimetallic oxide clusters with 3,5‐bis(3‐pyridyl)‐1,2,4‐triazole ligands

In the title organic–inorganic hybrid complex, poly[[[μ‐3,5‐bis(3‐pyridyl)‐1,2,4‐triazole]tri‐μ₃‐oxido‐tetra‐μ₂‐oxido‐oxidodicobalt(II)dimolybdenum(VI)] monohydrate], {[Co₂Mo₂O₈(C₁₂H₉N₅)]·H₂O}_n, the asymmetric unit is composed of two Co^II centers, two [Mo^VIO₄] tetrahedral units, one neutral 3,5‐bis(3‐pyridyl)‐1,2,4‐triazole (BPT) ligand and one solvent water molecule. The cobalt centers both exhibit octahedral [CoO₅N] coordination environments. Four Co^II and four Mo^VI centers are linked by μ₂‐oxide and/or μ₃‐oxide bridges to give an unprecedented bimetallic octanuclear [Co₄Mo₄O₂₂N₄] cluster, which can be regarded as the first example of a metal‐substituted octamolybdate and exhibits a structure different from those of the eight octamolybdate isomers reported to date. The bimetallic oxide clusters are linked to each other through corner‐sharing to give two‐dimensional inorganic layers, which are further bridged by trans‐BPT ligands to generate a three‐dimensional organic–inorganic hybrid architecture with six‐connected distorted α‐Po topology.     

Optically Active Transition Metal Complexes. 128 [1] Synthesis,Characterization and Molecular Structures of Cycloheptatrienyl‐Iminphos‐Molybdenum Complexes Differing Only in the Metal Configuration

The chiral‐at‐metal cycloheptatrienyl‐molybdenum complexes (R_Mo, S_C)‐[(η⁷‐C₇H₇)Mo(iminphos)(CO)]BF₄ ( 2a ) and (S_Mo, S_C)‐[(η⁷‐C₇H₇)Mo(iminphos)(CO)]BF₄ ( 2b ) (iminphos = 2‐[N‐(S)‐1‐phenylethylcarbaldimino]phenyl(diphenyl)phosphane), which only differ in the molybdenum configuration, were prepared and separated by fractional crystallization. The absolute configuration for both diastereomers was determined by X‐ray analysis. ¹H NMR studies demonstrated the configurational lability at the molybdenum centre in solution.     

Über verschiedene Reaktionen der CO-verbrückten Komplexe [Mo(CO)3bipy]2 und [Mo(CO)3phen]2 (bipy = 2,2′-Bipyridyl,phen = 1,10-Phenanthrolin)

The interaction of [Mo(CO)₃bipy]₂ with various monodentate ligands L (L = NH₃, pyr, P(C₆H₅)₃, P(C₆H₅)Cl₂, CN^?, SO₂) yields, according to the reaction equation in ?Inhaltsübersicht”?, mixed tricarbonyl compounds Mo(CO)₃bipyL by cleavage of the CO bridges of the dimeric starting carbonyl. Oxidation of [Mo(CO)₃D]₂ (D = bipy, phen) by means of iodine, partly in the presence of free bipy or phen, leads to the covalent and ionic, respectively, compound types [Mo^II(CO)₃DI₂]₂, [Mo^I(CO)₂DI]₂, [Mo^II(CO)₂D₂I]I and [Mo^II(CO)₂D₂I]I₃.     

Dinitrogen Activation by Fryzuk’s [Nb(P2N2)] Complex and Comparison with the Laplaza–Cummins [Mo{N(R)Ar}3] and Schrock [Mo(N3N)] Systems

The reaction profile of N₂ with Fryzuk’s [Nb(P₂N₂)] (P₂N₂=PhP(CH₂SiMe₂NSiMe₂CH₂)₂PPh) complex is explored by density functional calculations on the model [Nb(PH₃)₂(NH₂)₂] system. The effects of ligand constraints, coordination number, metal and ligand donor atom on the reaction energetics are examined and compared to the analogous reactions of N₂ with the three‐coordinate Laplaza‐Cummins [Mo{N(R)Ar}₃] and four‐coordinate Schrock [Mo(N₃N)] (N₃N=[(RNCH₂CH₂)₃N]^3?) systems. When the model system is constrained to reflect the geometry of the P₂N₂ macrocycle, the N? N bond cleavage step, via a N₂‐bridged dimer intermediate, is calculated to be endothermic by 345 kJ mol^?1. In comparison, formation of the single‐N‐bridged species is calculated to be exothermic by 119 kJ mol^?1, and consequently is the thermodynamically favoured product, in agreement with experiment. The orientation of the amide and phosphine ligands has a significant effect on the overall reaction enthalpy and also the N? N bond cleavage step. When the ligand constraints are relaxed, the overall reaction enthalpy increases by 240 kJ mol^?1, but the N₂ cleavage step remains endothermic by 35 kJ mol^?1. Changing the phosphine ligands to amine donors has a dramatic effect, increasing the overall reaction exothermicity by 190 kJ mol^?1 and that of the N? N bond cleavage step by 85 kJ mol^?1, making it a favourable process. Replacing Nb^II with Mo^III has the opposite effect, resulting in a reduction in the overall reaction exothermicity by over 160 kJ mol^?1. The reaction profile for the model [Nb(P₂N₂)] system is compared to those calculated for the model Laplaza and Cummins [Mo{N(R)Ar}₃] and Schrock [Mo(N₃N)] systems. For both [Mo(N₃N)] and [Nb(P₂N₂)], the intermediate dimer is calculated to lie lower in energy than the products, although the final N? N cleavage step is much less endothermic for [Mo(N₃N)]. In contrast, every step of the reaction is favourable and the overall exothermicity is greatest for [Mo{N(R)Ar}₃], and therefore this system is predicted to be most suitable for dinitrogen cleavage.     

The Role of 2,6‐Diaminopyridine Ligands in the Isolation of an Unprecedented,Low‐Valent Tin Complex

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition‐metal chemistry. However, the stabilization of main‐group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6‐[ArNH‐CH₂]₂(NC₅H₃) (Ar=C₆H₃‐2,6‐iPr₂)) with Sn[N(SiMe₃)₂]₂ produces the DIMPYSn complex (DIMPY=(2,6‐[ArN?CH]₂(NC₅H₃)) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low‐valent Sn^II complexes, including a [DIMPYSn^IICl]⁺[SnCl₃]^? ion pair, a bisstannylene DAMPY{Sn^II[N(SiMe₃)₂]₂}₂, and the enamine complex MeDIMPYSn^II, were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and ¹¹⁹Sn Mössbauer spectroscopy.     

A mixed‐valence chair‐like tetranuclear copper(I,II) cluster with three linking modes of the 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole ligand

In the tetranuclear copper complex tetrakis[μ‐3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]bis[3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]dicopper(I)dicopper(II) dihydrate, [Cu^I₂Cu^II₂(C₁₂H₈N₅)₆]·2H₂O, the asymmetric unit is composed of one Cu^I center, one Cu^II center, three anionic 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole (2‐BPT) ligands and one solvent water molecule. The Cu^I and Cu^II centers exhibit [Cu^IN₄] tetrahedral and [Cu^IIN₆] octahedral coordination environments, respectively. The three independent 2‐BPT ligands adopt different chelating modes, which link the copper centers to generate a chair‐like tetranuclear metallomacrocycle with metal–metal distances of about 4.4 × 6.2 Å disposed about a crystallographic inversion center. Furthermore, strong π–π stacking interactions and O—H...N hydrogen‐bonding systems link the tetracopper clusters into a two‐dimensional supramolecular network.