Four‐ and Five‐Coordinate Gallium Complexes Stabilized by Bidentate 2‐(Dimethylaminomethyl)Pyrrole Ligand: Molecular Structures of Ga[NC4H3(CH2NMe2)‐2]3 and GaMe2[NC4H3(CH2NMe2)‐2]

Treatment of GaCl₃ with one equiv of Li[NC₄H₃(CH₂NMe₂)‐2] (n = 1, 2, 3) in diethyl ether at ?78 °C yields GaCl_3‐n[NC₄H₃(CH₂NMe₂)‐2]_n (n = 1, 1 ; n = 2, 2 ; n = 3, 3 ). Compound 1 reacts with two equiv of RLi to afford GaR₂[NC₄H₃(CH₂NMe₂)‐2] ( 4a, R=Me; 4b, R=Bu ) via transmetallation. Reacting 2 with one equiv of RLi in diethyl ether, 3 and 4 are formed via ligand redistribution. Variable temperature ¹H NMR spectroscopic experiments reveal that the five‐coordinate gallium compound 3 is fluxional and results in a coalescence temperature at 5 °C, at which ΔG^≠ is calculated at ca. 10.4 Kcal/mole. All the new compounds have been characterized by ¹H and ¹³C NMR spectroscopy and the structures of compounds 3 and 4a have also been determined by X‐ray crystallography.     

The Flipping of CO Ligand Groups in Metal Carbonyl Compounds and its Frequency in Fe(CO)5

It has been proven qualitatively by a number of authors using variable temperature NMR experiments that most metal carbonyl complexes are nonrigid. A quantitative determination of the ligand exchange frequency v_e is often achieved by a line shape analysis or by measurement of the transverse relaxation time T₂ using the Carr-Purcell method. In the case of a “very fast” exchange, however, both methods prove unsuccessful. It is shown in this study that a simultaneous fit of IR or Raman spectra on the one hand and NMR spectra on the other can make possible the determination of v_e for the “very fast” exchange and can also facilitate the determination of v_e in “slow” and “medium” exchange cases considerably. The ligand exchange frequency thus found for Fe(CO)₅, 1.1 × 10¹⁰s^?1, is unexpectedly high; comparison with variable temperature measurements on solid Fe(CO)₅, yields similar energy barriers. A mechanism of exchange closely related to the “Berry mechanism” is proposed. Finally the consequences of this surprisingly large ligand exchange rate are discussed with respect to IR band assignments for molecular “fragments” M(CO)^x (where x=coordination number, and M is a transition metal, typically lanthanoid or actinoid).     

2-噻吩乙醛酸-三苯基氧化膦-铕配合物的合成、结构表征及荧光性能的研究

用硝酸铕、2-噻吩乙醛酸(HL)和三苯基氧化膦(TPPO)合成了一种新型固体发光配合物;用元素分析、电导率、红外光谱和核磁共振确定了该配合物的分子式为EuL3TPPPO((H2O)2;在室温下测定了该配合物的荧光激发光谱和发射光谱;配合物中Eu(Ⅲ)离子的3个主要跃迁5D0→7F1,5D0→7F2和5D0→7F4分别位于593.4,618.8和699.4 nm.该固体配合物于室温下被紫外灯照射可以发出很强的红色荧光.IR光谱中2-噻吩乙醛酸在与稀土铕离子形成配合物后,vas(-COO-)由钠盐的1632 cm-1移至1612 cm-1,vs(-COO-)由1389 cm-1移至1409cm-1;vc=o(α-酮基)由HL的1654 cm-1移至1662 cm-1.配合物的vEu-o吸收峰出现在541 cm-1.在1HNMR谱图中,噻吩环上的3个氢原子的化学位移在形成配合物后移向高场;三苯基氧化膦中苯环上5种不同环境的质子的化学位移在形成配合物后向低场移动.TG分析证明,该固态配合物于空气中在常温至190℃以内是稳定的.     

Synthesis, Crystal Structure Determination, and Physicochemical Study of the Nickel(II) Complex of 4-(Pyridyl-2)-1,2,4-triazole

A new trinuclear nickel(II) complex with 4-(pyridyl-2)-1,2,4-triazole (pytrz), [Ni₃(pytrz)₆(H₂O)₆](NO₃)₆, has been synthesized, and its crystal structure has been determined. The compound was studied by X-ray phase analysis (XRPA), magnetochemical measurements, and electronic and IR spectroscopy.     

Neutral solvent/crown ether interactions 3. Reorientation of the hydrogen bonds in the low temperature (−150°C) structure of 18-crown-6·2(CH3NO2)

The title complex was crystallized from a saturated solution of 18-crown-6 in nitromethane at 5°C and cooled to –150°C prior to X-ray diffraction data collection. At –150° C 18-crown-6·2(CH₃NO₂) is monoclinic,P2₁/_n witha=9.290(2),b=7.864(6),c=13.627(8) Å, =1000.84(4)° andD _calc=1.31 g cm^–3 for Z=2. Leastsquares refinement using 1521 independent observed reflections [F _o5(F _o)] led to a final conventionalR value of 0.041. The complex at –150°C is isostructural with its room temperature structure with the exception of the orientation of the methyl hydrogen atoms and their crown ether oxygen interactions. The methyl group hydrogen atoms were fully refined isotropically. The crown ether resides around a center of inversion and hasD _3d symmetry. There is one methyl hydrogen...crown interaction at 2.35(3) Å, one apparently bifurcated hydrogen bond utilizing a second methyl hydrogen atom (2.55(3), 2.65(3) Å) and the third hydrogen atom is actually directed away from the crown ring (closest H...O contact=2.67(3) Å). Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82048 (5 pages).For part 2, see reference [24].     

Dipole moments of some substituted benzaldehydes. Conformational preference of substituents ortho to the aldehyde group

The dipole moments of a number of substituted benzaldehydes are measured in benzene solution. The angle which the dipole axis of the CHO group makes with the axis of rotation of the group is determined. The observed moments of the ortho-substituted benzaldehydes are compared with the moments calculated for free rotation as well as fors-trans ands-cis orientations of the -CHO group.o-Fluorobenzaldehyde exists mostly in thes-trans conformation.o-Chloro-,o-bromo-ando-nitro-benzaldehydcs also exist in thes-trans conformation; their observed dipole moments are even lower than the values calculated fors-trans forms, indicating mutual induction of the ortho substituents. Though 2,5-dichlorobenzaldehyde is expected to have the same dipole moment as benzaldehyde, the observed moment is significantly lower due to mutual induction of the ortho substituents. 2,5-Dimethylbcnzaldehyde has, however, almost the same moment as benzaldehyde. The dipole moment ofo-methoxybcnzaldchyde is considerably higher than the values calculated for boths-cis ands-trans conformations. An explanation is given for this.o-Hydroxybenzaldehyde exists exclusively in thes-cis form due to internal H-bonding.     

A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

Pentacarbonylpyrazinetungsten(0), (CO)₅W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)₅W(pyz)W(CO)₅ plus free pyrazine. These three species exist at equilibrium. Using the quantitative ¹H NMR spectroscopy, the equilibrium constant could be determined to be K_eq = (5.9 ± 0.8) × 10⁻² at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)₄(pyz)₂ was found to be less stable than W(CO)₅(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)₄[P(OCH₃)₃](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)₄[P(OCH₃)₃](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, ¹H, ¹³C, and ³¹P NMR spectroscopy.     

乙二胺双缩5-氯水杨醛Sclliff碱铜配合物的合成及晶体结构

合成了N,N′-二(5-氯水杨醛)缩乙二胺合铜配合物([Cu(5-ClSalen)]),用单晶X射线衍射法测定了晶体结构.其晶体属三斜晶系,空间群P-1,晶胞参数a=0.83285(1)nm,b=0.95170(4)nm,c=1.09304(4)nm,α=115.130(2)°,β=94.694(2)°,γ=101.127(2)°,V=0.75642(4)nm3,分子式C16H12Cl2CuN2O2,Mr=398.72,Z=2,Dc=1.751g/cm3.在配合物中,Cu处于两个氮原子和两个酚氧原子形成的平面四方场中.     

High-resolution solid-state MAS 73Ge NMR spectra of some organogermanes

High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium.     

Complexes of tantalum with triaryloxides: Ligand and solvent effects on formation of hydride derivatives

A family of tantalum compounds supported by the triaryloxide [R-L]³⁻ ligands are reported [H₃(R-L) = 2,6-bis(4-methyl-6-R-salicyl)-4-tert-butylphenol, where R = Me or ^tBu]. The reaction of H₃[Me-L] with TaCl₅ in toluene gave [(Me-L)TaCl₂]₂ (1). The [^tBu-L] analogue [(^tBu-L)TaCl₂]₂ (2) was synthesized via treatment of TaCl₅ with Li₃[^tBu-L]. A THF solution of LiBHEt₃ was added to 1 in toluene to provide [(Me-L)TaCl(THF)]₂ (3), while treatment of 2 with 2 equiv of LiBHEt₃ or potassium in toluene followed by recrystallization from DME resulted in formation of [M(DME)₃][{(^tBu-L)TaCl}₂(μ-Cl)] [M = Li (4a), K (4b)]. When the amount of MBHEt₃ (M = Li, Na, K) was increased to 5 equiv, the analogous reactions in toluene afforded [{(bit-^tBu-L)Ta}₂(μ-H)₃M] [M = Li(THF)₂ (5a), Na(DME)₂ (5b), K(DME)₂ (5c)]. During the course of the reaction, the methylene CH activation of the ligand took place. Dissolution of 5a in DME produced [{(bit-^tBu-L)Ta}₂(μ-H)₃Li(DME)₂] (6), indicating that the coordinated THF molecules are labile. When the 2/LiBHEt₃ reaction was carried out in THF, the ring opening of THF occurred to yield [(^tBu-L)Ta(OBuⁿ)₂]₂ (7) along with a trace amount of [Li(THF)₄][{(^tBu-L)TaCl}₂(μ-OBuⁿ)] (8). Treatment of 2 with potassium hydride in DME yielded [{(^tBu-L)TaCl₂K(DME)₂}₂(μ-OCH₂CH₂O)] (9), in which the ethane-1,2-diolate ligand arose from partial C-O bond rupture of DME. The X-ray crystal structures of 2, 3, 4, 5a, 6, 7, and 9 are described.