Recent Developments in the Chemistry of Pn(I) (Pn=N,P, As,Sb, Bi) Cations

The Group 15 Pn(I) cations (Pn=N, P, As, Sb and Bi), which are isoelectronic with the donor-stabilized carbones, have emerged recently. Despite the presence of two lone pair of electrons, the Pn(I) cations are weakly nucleophilic due to their inherent positive charge. Strongly electron-donating supporting ligands including zwitterionic forms have been used to enhance their Lewis basicity. Furthermore, the chelating effect of cyclic ligand systems proved effective in increasing their nucleophilicity. The strategies involved in successfully isolating the fleeting Sb(I) and Bi(I) cations as the recent most achievements in this field have been discussed. The syntheses, structure, bonding situations and reactivity of the Pn(I) cations are discussed. An outlook on the periodic trends and future applications of these electronically unique electron-rich cationic moieties have been provided.     

Synthesis and characterization of the "metallic salts" A5Pn4 (A = K, Rb, Cs and Pn = As, Sb, Bi) with isolated zigzag tetramers of Pn4(4-) and an extra delocalized electron

The isostructural title compounds were prepared by direct reactions of the corresponding elements, and their structures were determined from single-crystal X-ray diffraction data in the monoclinic space group C2/m, Z = 2 (K5As4, a = 11.592(2) A, b = 5.2114(5) A, c = 10.383(3) A, beta = 113.42(1) degrees; K5Sb4, a = 12.319(1) A, b = 5.4866(4) A, c = 11.258(1) A, beta = 112.27(7) degrees; Rb5Sb4, a = 12.7803(9) A, b = 5.7518(4) A, c = 11.6310(8) A, beta = 113.701(1) degrees; K5Bi4, a = 12.517(2) A, b = 5.541(1) A, c = 11.625(2) A, beta = 111.46(1) degrees; Rb5Bi4, a = 12.945(4) A, b = 5.7851(9) A, c = 12.018(5) A, beta = 112.78(3) degrees; Cs5Bi4, a = 12.887(3) A, b = 6.323(1) A, c = 12.636(1) A, beta = 122.94(2) degrees). The compounds contain isolated and flat zigzag tetramers of Pn4(4-) (Pnictide (Pn) = As, Sb, Bi) with a conjugated pi-electron system of delocalized electrons. All six compounds are metallic ("metallic salts") and show temperature-independent (Pauli-like) paramagnetism due to a delocalized electron from the extra alkali-metal cation in the formula. At low temperatures (around 9.5 K) and low magnetic fields the bismuthides become superconducting.     

The analytical and descriptive inorganic chemistry of the hydrolysis of hexafluoropnictate ions, PnF6 (Pn = P, As, Sb, Bi)

The rates of aqueous hydrolysis of the hexafluoropnictate ions, PnF₆⁻ (Pn=P, As, Sb, Bi) were determined using a fluoride ion selective electrode and understood qualitatively in terms of ionic size and polarizability of the central atom. Both S_N2 and S_N1 (i.e. associative and dissociative) hydrolysis are discussed as are the competing roles of acid and base in the reaction. (Valence) isoelectronic analogies are also given. Regardless of the interpretation or reaction conditions, it is unequivocal that the hydrolysis rate is measurably rapid for the hexafluoroantimonate. By contrast, it is negligible for both hexafluorophosphate and hexafluoroarsenate.     

Actinide–Pnictide (An−Pn) Bonds Spanning Non‐Metal,Metalloid, and Metal Combinations (An=U,Th; Pn=P,As, Sb,Bi)

The synthesis and characterisation is presented of the compounds [An(Tren^DMBS){Pn(SiMe₃)₂}] and [An(Tren^TIPS){Pn(SiMe₃)₂}] [Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t)₃, An=U, Pn=P, As, Sb, Bi; An=Th, Pn=P, As; Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃, An=U, Pn=P, As, Sb; An=Th, Pn=P, As, Sb]. The U?Sb and Th?Sb moieties are unprecedented examples of any kind of An?Sb molecular bond, and the U?Bi bond is the first two‐centre‐two‐electron (2c–2e) one. The Th?Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U?Bi complex is the heaviest 2c–2e pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An?An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U?Pn bonds degrade by homolytic bond cleavage, whereas the more redox‐robust thorium compounds engage in an acid–base/dehydrocoupling route.     

Actinide–Pnictide (An−Pn) Bonds Spanning Non‐Metal,Metalloid, and Metal Combinations (An=U,Th; Pn=P,As, Sb,Bi)

The synthesis and characterisation is presented of the compounds [An(Tren^DMBS){Pn(SiMe₃)₂}] and [An(Tren^TIPS){Pn(SiMe₃)₂}] [Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t)₃, An=U, Pn=P, As, Sb, Bi; An=Th, Pn=P, As; Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃, An=U, Pn=P, As, Sb; An=Th, Pn=P, As, Sb]. The U−Sb and Th−Sb moieties are unprecedented examples of any kind of An−Sb molecular bond, and the U−Bi bond is the first two‐centre‐two‐electron (2c–2e) one. The Th−Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U−Bi complex is the heaviest 2c–2e pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An−An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U−Pn bonds degrade by homolytic bond cleavage, whereas the more redox‐robust thorium compounds engage in an acid–base/dehydrocoupling route.     

Valence compounds versus metals. Synthesis, characterization, and electronic structures of cubic Ae(4)Pn(3) phases in the systems Ae = Ca, Sr, Ba, Eu; Pn = As, Sb, Bi

The isostructural compounds Sr(4)Bi(3), Ba(4)Bi(3), and Ba(4)As( approximately )(2.60) were prepared by direct reactions of the corresponding elements and their structures determined from single-crystal X-ray diffraction data as anti-Th(3)P(4) type in the cubic space group I43d, Z = 4 (a = 10.101(1) A, 10.550(1) A, 9.973 (1) A, respectively). The two bismuth compounds are stoichiometric, and the arsenide refines as Ba(4)As(2.60(2)). Only unrelated phases are obtained for all binary combinations among the title components for either Ca or Sb. The magnetic susceptibility and resistivities of Ba(4)Bi(3) and Eu(4)Bi(3) show that they are good metallic conductors ( approximately 40 microomega.cm at 298 K), whereas Ba(4)As(2.60) exhibits rho(150) > 1000 microomega.cm. The electronic structures of Sr(4)Bi(3), Ba(4)Bi(3), and Ba(4)As(3) were calculated by TB-LMTO-ASA methods. Mixing of cation d states into somewhat disperse valence p bands on Bi results in empty bands at E(F) and metallic behavior, whereas the narrower valence band in the electron-deficient Ba(4)As(3) leads to vacancies in about 11% of the anion sites and a valence compound.     

Dicationic E4 Chains (E=P,As, Sb,Bi) Embedded in the Coordination Sphere of Transition Metals

The oxidation chemistry of the complexes [{CpMo(CO)₂}₂(μ,η²:η²‐E₂)] (E=P ( A ), As ( B ), Sb ( C ), Bi ( D )) is compared. The oxidation of A – D with [Thia]⁺ (=[C₁₂H₈S₂]⁺) results in the selective formation of the dicationic E₄ complexes [{CpMo(CO)₂}₄(μ₄,η²:η²:η²:η²‐E₄)]²⁺ (E=P ( 1 ), As ( 2 ), Sb ( 3 ), Bi ( 4 )), stabilized by four [CpMo(CO)₂] fragments. The formation of the corresponding monocations [ A ]⁺, [ C ]⁺, and [ D ]⁺ could not be detected by cyclic voltammetry, EPR, or NMR spectroscopy. This finding suggests that dimerization is fast and that there is no dissociation in solution, which was also predicted by DFT calculations. However, EPR measurements of 2 confirmed the presence of small amounts of the radical cation [ B ]⁺ in solution. Single‐crystal X‐ray diffraction revealed that the products 1 and 2 feature a zigzag E₄ chain in the solid state while 3 and 4 bear a central E₄ cage with a distorted “butterfly‐like” geometry. Additionally, 1 can be easily and reversibly converted into a symmetric and an unsymmetric form.     

吡咯同系物C4H4XH(X=N,P,As,Sb)二阶超极化率的理论研究

用ab initio HF，MP2和B3LYP三种方法的输出结果，根据完全态求和公式自编程序计算了吡咯同系物的二阶超极化率．结果表明随着杂原子序数的增大，体系的二阶超极化率也随着增大．从对称性出发，利用二态模型讨论了体系光学非线性增大的原因．从杂原子基团与吡咯同系物二阶超极化率之间所成的线性关系，可以得出决定体系非线性光学性质的主要因素是杂原子．与呋喃同系物的光克尔效应相比，吡咯同系物是具有良好应用前景的非线性光学材料．     

Zintl phase variations through cation selection. Synthesis and structure of A21Cd4Pn18 (A = Eu, Sr, Ba; Pn = Sb, Bi)

Four new Zintl compounds, Ba21Cd4Sb18, Ba21Cd4Bi18, Sr21Cd4Bi18, and Eu21Cd4Bi18, have been synthesized and structurally characterized. Despite the similarity in their chemical formulas and regardless of their identical electronic requirements, the structures of the Ba compounds and the Sr and Eu compounds are subtly different. Due to the cations, a cleavage of a selected pnicogen-cadmium bond occurs and the structures adapt to a novel packing of the resultant heteronuclear anions.     

Substituted iron selenocarboxylate complexes CpFe(CO)(EPh3)SeCOR (E = P,As, Sb)

Photolytic substitutions of iron selenocarboxylate complexes CpFe(CO)₂SeCOR with triphenylphosphine, triphenylarsine or triphenylantimony (EPh₃) gave exclusively the monosubstituted complexes CpFe(CO)(EPh₃)SeCOR [R = 3,5-C₆H₃(NO₂)₂ (1), 4-C₆H₄NO₂ (2), Ph (3), 2-C₆H₄Me (4), and E = P (a), As (b), Sb (c)] in high yields.     

E4 Transfer (E=P,As) to Ni Complexes

The use of [Cp′′₂Zr(η^1:1-E₄)] (E=P ( 1 a ), As ( 1 b ), Cp′′=1,3-di-tert-butyl-cyclopentadienyl) as phosphorus or arsenic source, respectively, gives access to novel stable polypnictogen transition metal complexes at ambient temperatures. The reaction of 1 a/1 b with [Cp^RNiBr]₂ (Cp^R=Cp^Bn (1,2,3,4,5-pentabenzyl-cyclopentadienyl), Cp′′′ (1,2,4-tri-tert-butyl-cyclopentadienyl)) was studied, to yield novel complexes depending on steric effects and stoichiometric ratios. Besides the transfer of the complete E_n unit, a degradation as well as aggregation can be observed. Thus, the prismane derivatives [(Cp′′′Ni)₂(μ,η^3:3-E₄)] ( 2 a (E=P); 2 b (E=As)) or the arsenic containing cubane [(Cp′′′Ni)₃(μ₃-As)(As₄)] ( 5 ) are formed. Furthermore, the bromine bridged cubanes of the type [(Cp^RNi)₃{Ni(μ-Br)}(μ₃-E)₄]₂ (Cp^R=Cp′′′: 6 a (E=P), 6 b (E=As), Cp^R=Cp^Bn: 8 a (E=P), 8 b (E=As)) can be isolated. Here, a stepwise transfer of E_n units is possible, with a cyclo-E₄²⁻ ligand being introduced and unprecedented triple-decker compounds of the type [{(Cp^RNi)₃Ni(μ₃-E)₄}₂(μ,η^4:4-E′₄)] (Cp^R=Cp^Bn, Cp′′′; E/E′=P, As) are obtained.     

杂硼原子簇B6X-(X=N, P, As, Sb, Bi)稳定性和芳香性研究

利用Gaussian 98程序, 采用从头算和密度泛函理论方法, 对B6X-(X=N, P, As, Sb, Bi)杂硼原子簇进行了理论研究, 优化得到了其稳定平衡构型, 讨论了其振动光谱和稳定性等, 通过自然键轨道(NBO)、分子轨道(MO)和核独立化学位移(NICS)分析, 确定这些杂硼原子簇都有离域的π电子和σ电子成键轨道, 满足4n+2电子规则, 具有芳香性, 与纯B6- 或B62- 原子簇呈反芳香性不同.     

Spurenelemente (Zn, Cu, As, Sb, P) in Siliciumcarbid

Ohne Zusammenfassung     

Emergence of superconductivity in "32522" structure of (Ca3Al2O(5-y))(Fe2Pn2) (Pn = As and P)

Using a high-pressure technique, we have successfully synthesized (Ca(3)Al(2)O(5-y))(Fe(2)Pn(2)) (Pn = As and P), the first iron-based superconductors with the perovskite-based "32522" structure to be reported. The transition temperature (T(c)) is 30.2 K for Pn = As and 16.6 K for Pn = P. The emergence of superconductivity is ascribed to the small tetragonal a-axis lattice constant of the materials. From these results, an empirical relationship is established between the a-axis lattice constant and T(c) in iron-based superconductors, which offers a practical guideline for exploring new superconductors with higher T(c).     

Fixation and Release of Intact E4 Tetrahedra (E=P,As)

By the reaction of [NacnacCuCH₃CN] with white phosphorus (P₄) and yellow arsenic (As₄), the stabilization and enclosure of the intact E₄ tetrahedra are realized and the disubstituted complexes [(NacnacCu)₂(μ,η^2:2‐E₄)] ( 1 a : E=P, 1 b : E=As) are formed. The mono‐substituted complex [NacnacCu(η²‐P₄)] ( 2 ), was detected by the exchange reaction of 1 a with P₄ and was only isolated using low‐temperature work‐up. All products were comprehensively spectroscopically and crystallographically characterized. The bonding situation in the products as intact E₄ units (E=P, As) was confirmed by theory and was experimentally proven by the pyridine promoted release of the bridging E₄ tetrahedra in 1 .