Six-coordinate NbF5 and TaF5 complexes with tertiary mono-phosphine and -arsine ligands

The syntheses of the extremely moisture sensitive, neutral [MF5(PR3)] (M = Nb or Ta, R = Me or Ph) and [MF5(AsR?3)] (R? = Me or Et), from reaction of the ligands with MF5 in anhydrous diethyl ether solution are reported. Attempts to isolate analogous complexes with SbMe3 were unsuccessful. The products are characterised by IR and mutinuclear NMR (1H, 19F{1H}, 31P{1H} and 93Nb) spectroscopic studies. These are the first examples of six-coordinate phosphine or arsine complexes of the Group 5 pentafluorides. The ionic species, trans-[MF4(PMe3)2][MF6], are obtained from diethyl ether solution of [MF5(PMe3)] containing excess PMe3 and similarly characterised. All complexes are extremely moisture and oxygen sensitive and decomposed by many common solvents. In solution in toluene the [MF5(PMe3)] (M = Nb or Ta) and [MF5(AsR?3)] are extensively dissociated at ambient temperatures. The [MF5(PPh3)] dissolve in CH2Cl2 with decomposition to form [PPh3H][MF6]. Attempts to isolate phosphine complexes of NbOF3 were unsuccessful

Coordination complexes of the tungsten(VI) oxide fluorides WOF4 and WO2F2 with neutral oxygen- and nitrogen-donor ligands

Abstract[WOF4(MeCN)], prepared from a 1:1 ratio of WF6 and O(SiMe3)2 in MeCN, is a convenient synthon for the preparation of complexes of WOF4 and WO2F2 with neutral N- or O-donor ligands. It reacts with monodentate ligands L (L=OPPh3, OPMe3, dmso, py) in a 1:1 ratio to form [WOF4L], whilst reaction of [WOF4(MeCN)], O(SiMe3)2 and L⿲ (L⿲=OPPh3, py, pyNO, dmso) in 1:1:2 ratio affords [WO2F2L⿲2]. The synthesis of [WO2F2(L-L)] (L-L=Ph2P(O)CH2P(O)Ph2 or 1,10-phenanthroline) are also described. Similar complexes with arsines, thio- or seleno-ethers are not formed by these routes. The complexes have been characterised by microanalysis, IR, 1H and 19F{1H} NMR spectroscopy, and X-ray crystal structures are reported for [WOF4(OPPh3)], [WO2F2(OPPh3)2], [WO2F2{Ph2P(O)CH2P(O)Ph2}] and [WO2F2(pyNO)2]

Cross Contrastive Feature Perturbation for Domain Generalization

Domain generalization (DG) aims to learn a robust model from source domains that generalize well on unseen target domains. Recent studies focus on generating novel domain samples or features to diversify distributions complementary to source domains. Yet, these approaches can hardly deal with the restriction that the samples synthesized from various domains can cause semantic distortion. In this paper, we propose an online one-stage Cross Contrasting Feature Perturbation (CCFP) framework to simulate domain shift by generating perturbed features in the latent space while regularizing the model prediction against domain shift. Different from the previous fixed synthesizing strategy, we design modules with learnable feature perturbations and semantic consistency constraints. In contrast to prior work, our method does not use any generative-based models or domain labels. We conduct extensive experiments on a standard DomainBed benchmark with a strict evaluation protocol for a fair comparison. Comprehensive experiments show that our method outperforms the previous state-of-the-art, and quantitative analyses illustrate that our approach can alleviate the domain shift problem in out-of-distribution (OOD) scenarios

Synthesis of small-ring benzannulated triphosphamacrocycles by template methods

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Efficient and Provably Secure Certificateless Signcryption from Bilinear Maps

Signcryption is a cryptographic primitive that fulfills both the functions of digital signature and public key encryption simultaneously, at a cost significantly lower than that required by the traditional signature-then-encryption approach. In 2008, Barbosa and Farshim introduced the notion of certificateless signcryption (CLSC) and proposed the first CLSC scheme [2], but which requires six pairing operations in the signcrypt and unsigncrypt phases. In this paper, aimed at designing an efficient CLSC scheme, we propose a new efficient CLSC scheme from bilinear maps, which requires only two pairing operations in the signcrypt and unsigncrypt phases and is more efficient than all the schemes available