Theoretical studies on the structures, material properties, and IR spectra of polymorphs of 3,4-bis(1H-5-tetrazolyl)furoxan.

Theoretical studies on the structures, densities, and heats of formation of conformational isomers of 3,4-bis(1H-5-tetrazolyl)furoxan (H2BTF) were performed based on density functional theory (DFT) calculations. Two stable planar conformational isomers, the face-to-back and the back-to-face conformers, and one stable slightly twisted conformer, the back-to-back conformer, were predicted for H2BTF at the M06-2X/6-311 + G(d,p) level of theory. The face-to-back conformer was calculated to be the most stable conformational isomer on the potential energy surface. No stable face-to-face conformer, whether planar or tilted, was identified in the calculations. The Vienna Ab Initio Simulation Package (VASP) was used in combination with molecular dynamics simulation to explore the stable crystal forms and the densities of the stable conformational isomers. Two of them exhibited high densities: the face-to-back conformer with P21 symmetry (2.01 g/cm3) and the back-to-back conformer with Pna21 symmetry (2.05 g/cm3). Their heats of formation were also predicted to be high when calculated at the same DFT level. The detonation pressures and velocities of these polymorphs, as calculated using the EXPLO5 program, are well above those of many advanced high energy density materials, pointing to the potential use of these conformers as novel explosives with good detonation performance. Also, IR spectra are shown to be able to distinguish these denser polymorphs of H2BTF. This study suggests that it could be worth investigating whether denser polymorphs of H2BTF can be grown.

Reactivity of an amidinato silylene and germylene toward germanium(ii), tin(ii) and lead(ii) halides.

The coordination chemistry of an amidinato silylene and germylene toward group 14 element(ii) halides is described. The reaction of the amidinato silicon(ii) amide [LSiN(SiMe3)2] (1, L = PhC(NtBu)2) with SnCl2 and PbBr2 afforded the amidinato silylene-dichlorostannylene and -dibromoplumbylene adducts [L{(Me3Si)2N}SiEX2] (E = Sn, X = Cl (2); E = Pb, X = Br (3)), respectively, in which there is a lone pair of electrons on the Sn(ii) and Pb(ii) atoms. X-ray crystallography, NMR spectroscopy and theoretical studies show conclusively that the Si(ii)-E(ii) bonds are donor-acceptor interactions. Similar electronic structures were found in the amidinato germylene-dichlorogermylene and -dichlorostannylene adducts [L{(Me3Si)2N}GeECl2] (E = Ge (5), Sn (6)), which were prepared by treatment of the amidinato germanium(ii) amide [LGeN(SiMe3)2] (4) with GeCl2·dioxane and SnCl2, respectively.

Delocalized Hypervalent Silyl Radical Supported by Amidinate and Imino Substituents.

The reaction of the amidinato silylsilylene with a functionalized diaminochlorosilyl substituent, [LSiSi(Cl){(NtBu)2C(H)Ph}] (1; L = PhC(NtBu)2), with ArN═C═NAr (Ar = 2,6-iPr2C6H3) in toluene afforded the delocalized hypervalent silyl radical [LSi•(µ-CNAr)2Si{(NtBu)2C(H)Ph}] (2). It possesses a hypervalent silyl radical that delocalizes throughout the Si2C2 ring.

Transumbilical Single-Site Laparoscopic Inguinal Hernia Inversion and Ligation in Girls.

OBJECTIVES: The combination of transumbilical single-site laparoscopic inguinal hernia inversion and ligation is a new approach for girls. We have done 13 cases in our hospital since May 2013. MATERIALS AND METHODS: Thirteen girls with inguinal hernia, from 6 months to 10 years of age, were treated with transumbilical single-site laparoscopy. RESULTS: None of the patients underwent conversion from single-site laparoscopy to the open approach or conventional laparoscopic surgery. The average operation time was 35.15±6.68 minutes. Four cases were found to have a contralateral inguinal hernia. The patients were discharged the day after operation. Follow-up of 7 months to a year with all cases showed no recurrence and no incision complication. CONCLUSIONS: The combination of transumbilical single-site laparoscopic inguinal hernia inversion and ligation is a reliable, safe, and cosmetic herniorrhaphy for girls with inguinal hernia.

Group II metal complexes of the germylidendiide dianion radical and germylidenide anion.

The two-electron reduction of a Group 14-element(I) complex [RË⋅] (E=Ge, R=supporting ligand) to form a novel low-valent dianion radical with the composition [RË:]˙(2-) is reported. The reaction of [LGeCl] (1, L=2,6-(CH=NAr)2C6H3, Ar=2,6-iPr2C6H3) with excess calcium in THF at room temperature afforded the germylidenediide dianion radical complex [LGe]˙(2-)⋅Ca(THF)3(2+) (2). The reaction proceeds through the formation of the germanium(I) radical [LGe⋅], which then undergoes a two-electron reduction with calcium to form 2. EPR spectroscopy, X-ray crystallography, and theoretical studies show that the germanium center in 2 has two lone pairs of electrons and the radical is delocalized over the germanium-containing heterocycle. In contrast, the magnesium derivative of the germylidendiide dianion radical is unstable and undergoes dimerization with concurrent dearomatization to form the germylidenide anion complex [C6H3-2-{C(H)=NAr}Ge-Mg-6-{C(H)-NAr}]2 (3).

An extensive n, π, σ-electron delocalized Si(4) ring.

The tetrasilacyclobutadiene [LSi(µ-SiL')2 SiL] (L=PhC(NtBu)2 , L'=2,6-iPr2 C6 H3 NSiMe3 ) consists of an aromatic silicon-containing four-membered ring in which two π, two σ, and two lone-pair electrons are cyclically delocalized. The electron delocalization was illustrated by theoretical studies and reactivity with elemental sulfur to form the allylic zwitterionic cyclic compound [(LSi)2 (µ-SiL')(µ-Si(S)L')] with 2π-electron delocalization along the Si3 skeleton.

Zwitterionic base-stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene.

The syntheses of a zwitterionic base-stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene supported by amidinates and low-valent germanium amidinate substituents are described. The reaction of the amidinate Ge(I) dimer, [LGe:]2 (1, L=PhC(NtBu)2 ), with two equivalents of the amidinate tin(II) chloride, [LSnCl] (2), and KC8 in tetrahydrofuran (THF) at room temperature afforded a mixture of the zwitterionic base-stabilized digermadistannacyclobutadiene, [L2 Ge2 Sn2 L'2 ] (3; L'=LGe:), and the bis(amidinate) tin(II) compound, [L2 Sn:] (4). Compound 3 can also be prepared by the reaction of 1 with [L(Ar) SnCl] (5, L(Ar) =tBuC(NAr)2 , Ar=2,6-iPr2 C6 H3 ) in THF at room temperature. Moreover, the reaction of 1 with the "onio-substituent transfer" reagent [4-NMe2 -C5 H4 NSiMe3 ]OTf (8) in THF and 4-(N,N-dimethylamino)pyridine (DMAP) at room temperature afforded a mixture of the zwitterionic base-stabilized tetragermacyclobutadiene, [L4 Ge6 ] (9), the amidinium triflate, [PhC(NHtBu)2 ]OTf (10), and Me3 SiSiMe3 (11). X-ray structural data and theoretical studies show conclusively that compounds 3 and 9 have a planar and rhombic charge-separated structure. They are also nonaromatic.

A silyliumylidene cation stabilized by an amidinate ligand and 4-dimethylaminopyridine.

The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4-dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [LSi:]2 (1; L = PhC(NtBu)2) with one equivalent of N-trimethylsilyl-4-dimethylaminopyridinium triflate [4-NMe2C5H4NSiMe3]OTf and two equivalents of DMAP in THF afforded [LSi(DMAP)]OTf (2). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [L'2(L)Si]OTf (3; L' = LSi:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)3}] and elemental sulfur in THF afforded the silylsilylene [LSiSi(H){(NtBu)2C(H)Ph}] (4) and the base-stabilized silanethionium triflate [LSi(S)DMAP]OTf (5), respectively. Compounds 2, 3, and 5 have been characterized by X-ray crystallography.

Reactivity of a tin(II) (iminophosphinoyl)(thiophosphinoyl)methanediide complex toward sulfur: synthesis and 119Sn Mössbauer spectroscopic studies of [{(µ-S)SnC(PPh2═NSiMe3)(PPh2═S)}3Sn(µ3-S)].

Reaction of [(PPh(2)═NSiMe(3))(PPh(2)═S)CSn:](2) (1) with elemental sulfur in toluene afforded [{(µ-S)Sn(IV)C(PPh(2)═NSiMe(3))(PPh(2)═S)}(3)Sn(II)(µ(3)-S)] (2) and [CH(2)(PPh(2)═NSiMe(3))(PPh(2)═S)] (3). Compound 2 comprises a Sn(II)S moiety coordinated with the Sn(IV) and S atoms of a trimeric 2-stannathiomethendiide {(PPh(2)═NSiMe(3))(PPh(2)═S)CSn(µ-S)}(3). Compound 2 has been characterized by NMR spectroscopy, (119)Sn Mössbauer studies, X-ray crystallography, and theoretical studies. (119)Sn NMR spectroscopy and Mössbauer studies show the presence of Sn(IV) and Sn(II) atoms in 2. X-ray crystallography suggests that the Sn(II)S moiety does not have multiple bond character. Theoretical studies illustrate that the C(methanediide)-Sn bonds comprise a lone pair orbital on each C(methanediide) atom and an C-Sn occupied σ orbital.

Synthesis and characterization of a singlet delocalized 2,4-diimino-1,3-disilacyclobutanediyl and a silylenylsilaimine.

The synthesis and characterization of a singlet delocalized 2,4-diimino-1,3-disilacyclobutanediyl, [LSi(µ-CNAr)(2)SiL] (2, L: PhC(NtBu)(2), Ar: 2,6-iPr(2) C(6) H(3)), and a silylenylsilaimine, [LSi(=NAr)-SiL] (3), are described. The reaction of three equivalents of the disilylene [LSi-SiL] (1) with two equivalents of ArN=C=NAr in toluene at room temperature for 12 h afforded [LSi(µ-CNAr)(2)SiL] (2) and [LSi(=NAr)-SiL] (3) in a ratio of 1:2. Compounds 2 and 3 have been characterized by NMR spectroscopy and X-ray crystallography. Compound 2 was also investigated by theoretical studies. The results show that compound 2 possesses singlet biradicaloid character with an extensive electronic delocalization throughout the Si(2)C(2) four-membered ring and exocyclic C=N bonds. Compound 3 is the first example of a silylenylsilaimine, which contains a low-valent silicon center and a silaimine substituent. A mechanism for the formation of 2 and 3 is also proposed.

An amidinate-stabilized germatrisilacyclobutadiene ylide.

The synthesis and characterization of new amidinate-stabilized germatrisilacyclobutadiene ylides [L(3)Si(3)GeL'] (L=PhC(NtBu)(2); L'=ËL; Ë=Ge (3), Si (7)) are described. Compound 3 was prepared by the reaction of [LSi-SiL] (1) with one equivalent of [LGe-GeL] (2) in THF. Compound 7 was synthesized by the reaction of 2 with excess 1 in THF. The bisamidinate germylene [L(2)Ge:] (4) is a by-product in both reactions. Moreover, compound 7 was prepared by the reaction of 3 with one equivalent of 1 in THF. Compounds 3 and 7 have been characterized by NMR spectroscopy, X-ray crystallography, and theoretical studies. The results show that compounds 3 and 7 are not antiaromatic. The puckered Si(3) Ge four-membered rings in 3 and 7 have a ylide structure, which is stabilized by amidinate ligands and the electron delocalization within the Si(3) Ge four-membered ring.

Synthesis and characterization of an amidinate-stabilized cis-1,2-disilylenylethene [cis-LSi{C(Ph)=C(H)}SiL] and a singlet delocalized biradicaloid [LSi(µ(2)-C(2)Ph(2))(2)SiL].

The synthesis and characterization of novel cis-1,2-disilylenylethene [cis-LSi{C(Ph)=C(H)}SiL] (2; L=PhC(NtBu)(2)) and a singlet delocalized biradicaloid [LSi(µ(2)-C(2)Ph(2))(2)SiL] (3) are described. Compound 2 was prepared by the reaction of [{PhC(NtBu)(2)}Si:](2) (1) with one equivalent of PhC[triple chemical bond]CH in toluene. Compound 3 was synthesized by the reaction of 1 with two equivalents of PhC[triple chemical bond]CPh in toluene. The results suggest that the reaction proceeds through an [LSi{C(Ph)==C(Ph)}SiL] intermediate, which then reacts with another molecule of PhC[triple chemical bond]CPh to form 3. Compounds 2 and 3 have been characterized by X-ray crystallography and NMR spectroscopy. X-ray crystallography and DFT calculations of 3 show that the singlet biradicals are stabilized by the amidinate ligand and the delocalization within the "Si(µ(2)-C(2)Ph(2))(2)Si" six-membered ring.

Hydrosilylation of a silicon(II) hydride: synthesis and characterization of a remarkable silylsilylene.

The synthesis and characterization of novel monomeric silylsilylenes [{PhC(NtBu)(2)}Si--Si{(NtBu)(2)C(H)Ph}R] (R=Cl (2), H (4)) are described. Compound 2 was prepared by the treatment of [{PhC(NtBu)(2)}SiHCl(2)] (1) with two equivalents of potassium graphite, whereas compound 4 was synthesized by the treatment of 1 with four equivalents of potassium graphite. The results suggest that silicon(II) hydride intermediate [{PhC(NtBu)(2)}SiH] was formed in the reduction, which underwent a hydrosilylation with the amidinate ligand of [{PhC(NtBu)(2)}SiR] (R=Cl or H) to form 2 and 4, respectively. The existence of [{PhC(NtBu)(2)}SiH] in solution was demonstrated by the treatment of [{PhC(NtBu)(2)}SiCl] (3) with [K{HB(iBu)(3)}]. Compounds 2 and 4 have been characterized by X-ray crystallography and NMR spectroscopy. The results show that compounds 2 and 4 are stable in solution or the solid state, and do not dimerize to form the corresponding disilene. DFT calculations show that the Si--Si bonds in 2 and 4 do not have multiple-bond character.

Synthesis and characterization of a tin(II) bis(phosphinoyl)methanediide complex: a stannavinylidene derivative.

The reaction of [CH(2)(PPh(2)=NSiMe(3))(PPh(2)=S)] (1) with two equivalents of [Sn{N(SiMe(3))(2)}(2)] in refluxing toluene afforded novel tin(II) bis(phosphinoyl)methanediide complex 3. The structure of compound 3 has been determined by X-ray crystallography and DFT calculations. The topological analysis of the electron densities of compound 3 was performed.

Reactivity of a disilylene [{PhC(NBu(t))(2)}Si](2) toward bromine: synthesis and characterization of a stable monomeric bromosilylene.

The reaction of the disilylene [{PhC(NBu(t))(2)}Si](2) (1) with 1 equiv of bromine in toluene afforded novel monomeric bromosilylene [{PhC(NBu(t))(2)}SiBr] (2). The result shows that the Si(I)-Si(I) bond in 1 was cleaved by bromine. An X-ray structure of compound 2 has been determined.

Silabutadienes. Internal rotations and pi-conjugation. A density functional theory study.

The potential energy surfaces (PESs) for internal rotation around the central single bond of nine silabutadienes, which include all possible mono-, di-, tri-, and tetrasilabutadienes, are investigated computationally by using DFT with the B3LYP functional and the 6-311+G(d,p) basis set. For 1-silabutadiene (3), 2-silabutadiene (4), 1,4-disilabutadiene (5), 2,3-disilabutadiene (6), and 1,3-disilabutadiene (7), the s-trans rotamer is the most stable. For 1,2-disilabutadiene (8), 1,2,3-trisilabutadiene (9), and 1,2,4-trisilabutadiene (10), all having a trans-bent SiSi double bond, the most stable conformers are those having an antiperiplanar (ap) structure. For tetrasilabutadiene (11), the global minimum is the gauche rotamer. The internal rotation barriers (RB) (relative to the global minimum) follow the order (kcal/mol) 5 (10.0) > 3 (7.4) > 1,3-butadiene (12, (6.6)) > 10 (4.9) > or = 7 (4.4) > or = 4 (4.0) approximately = 8 (3.9) > 9 (2.7) approximately = 6 (2.6) > 11 (2.4). The barriers are slightly smaller at CCSD(T)/cc-PVTZ, but the trend remains the same. The size of the rotation barrier is mainly dictated by the length of the central single bond; that is, it is the largest for dienes with the shorter C-C central bond (5, 3, and 12), and it is smaller for dienes with the longer Si-C and Si-Si central bonds. The strength of pi-conjugation in the s-trans conformers of silabutadienes was estimated by resonance stabilization energies (RE) calculated by using the Natural Bond Orbital (NBO) and Block Localized Wave function (BLW) methods and bond separation equations. A linear correlation is found between the barrier heights for internal rotation and pi-conjugation energies. The calculated RBs are significantly smaller than the corresponding REs, indicating that pi-resonance energies are not the only factor that dictate the RB, and therefore, RBs, although suitable for estimating trends in pi-conjugation in a series of compounds, cannot be used for estimating absolute resonance energies.

Bromine-loss and hydrogen-loss dissociations in low-lying electronic states of the CH3Br+ ion studied using multiconfiguration second-order perturbation theory.

Complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with an ANO-RCC basis were performed for the 1(2)A', 1(2)A", 2(2)A', and 2(2)A" states of the CH3Br+ ion. The 1(2)A' state is predicted to be the ground state. The 2(2)A' state is predicted to be a bound state. The adiabatic and vertical excitation energies and the relative energies at the molecular geometry were calculated, and the energetic results for 2(2)A' and 2(2)A" are in reasonable agreement with the experimental data. Potential energy curves (PECs) for Br-loss and H-loss dissociations from the four C(s) states were calculated at the CASPT2//CASSCF level and the electronic states of the CH3(+) and CH2Br(+) ions as the dissociation products were determined by checking the relative energies and geometries of the asymptote products along the PECs. In the Br-loss dissociation, the 1(2)A', 1(2)A", and 2(2)A' states correlate with CH3(+) (X1A1') and the 2(2)A" state correlates with CH3(+) (1(3)A"). The energy increases monotonically with the R(C-Br) value along the four Br-loss PECs. In the H-loss dissociation the 1(2)A', 1(2)A", 2(2)A', and 2(2)A" states correlate with the X(1)A(1), 1(3)A", 1(3)A', and 1(1)A" states (1(3)A' lying above 1(1)A") of CH2Br(+), respectively. Along the 2(2)A" H-loss PEC there is an energy barrier and the CASSCF wave functions at large R(C-H) values have shake-up ionization character. Along the 2(2)A' H-loss PEC there are an energy barrier and a minimum. At the end of the present paper we present a comprehensive review on the electronic states and the X-loss and H-loss dissociations of the CH(3)X(+) (X = F, Cl, and Br) ions on the basis of our previous studies and the present study.

F-loss and H-loss dissociations in low-lying electronic states of the CH3F+ ion studied using multiconfiguration second-order perturbation theory.

Complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with an atomic natural orbital basis were performed for the 1(2)A'', 1(2)A', 2(2)A', 2(2)A'', and 3(2)A' (X2E, A2A1, and B2E) states of the CH3F+ ion. The 1(2)A'' state is predicted to be the ground state, and the C(s)-state energy levels are different from those of the CH3Cl+ ion. The 2(2)A' (A2A1) state is predicted to be repulsive, and the calculated adiabatic excitation energies for 2(2)A'' and 3(2)A' are very close to the experimental value for the B state. The CASPT2//CASSCF potential energy curves (PECs) were calculated for F-loss dissociation from the five C(s) states and H-loss dissociation from the 1(2)A'', 1(2)A', and 2(2)A'' states. The electronic states of the CH3+ and CH2F+ ions as the dissociation products were carefully determined by checking the energies and geometries of the asymptote products, and appearance potentials for the two ions in different states are predicted. The F-loss PEC calculations for CH3F+ indicate that F-loss dissociation occurs from the 1(2)A'', 1(2)A', and 2(2)A' states [all correlating with CH3+(X1A1')], which supports the experimental observations of direct dissociation from the X and A states, and that direct F-loss dissociation can occur from the two Jahn-Teller component states of B2E, 2(2)A'' and 3(2)A' [correlating with CH3+(1(3)A'') and CH3+(1(3)A'), respectively]. Some aspects of the 3(2)A' Cl-loss PEC of the CH3Cl+ ion are inferred on the basis of the calculation results for CH3F+. The H-loss PEC calculations for CH3F+ indicate that H-loss dissociation occurs from the 1(2)A'', 1(2)A', and 2(2)A'' states [correlating with CH2F+(1(3)A''), CH2F+(X1A1), and CH2F+(1(1)A''), respectively], which supports the observations of direct dissociation from the X and B states. As the 2(2)A' H-loss PEC of CH3Cl+, the 2(2)A' H-loss PEC of CH3F+ does not lead to H + CH2X+, but the PECs of the two ions represent different types of reactions.