Structure prediction of large cationic phosphorus clusters

Two P, Ten P, White P, Red P: Mechanistic Exploration of the Oligomerization of Red Phosphorus from Diphosphorus with the Ab Initio Nanoreactor

Phosphorus is critical to humans on many fronts, yet we do not have a mechanistic understanding of some of its most basic transformations and reactions─namely the oligomerization of white phosphorus to red. With heat or under ultraviolet (UV) exposure, it has been experimentally demonstrated that white phosphorus dissociates into diphosphorus units which readily form red phosphorus. However, the mechanism of this process is unknown. The ab initio nanoreactor approach was used to explore the potential energy surface of phosphorus clusters. Density functional theory and metadynamics simulations were used to characterize potential reaction pathways. A mechanism for oligomerization is proposed to take place via diphosphorus additions at π-bonds and weak σ-bonds through three membered ring intermediates. Downhill paths through P6 and P8 clusters eventually result in P10 clusters that can oligomerize into red phosphorus chains. The initial, rate limiting step for this process has an energy barrier of 24.2 kcal/mol.

Medium-sized phosphorus cluster cations P+ 2m+1 (6 ≤ m ≤ 32) studied by collision-induced dissociation mass spectrometry

Medium-sized phosphorus cluster cations were generated by laser ablation of red phosphorus and investigated by the method of collision-induced dissociation mass spectrometry. Experimental results show that the primary dissociation channels of phosphorus cluster cations of P(+) 2m+1 (6 ≤ m ≤ 11) are all characterized by the loss of P4 unit. For larger cluster cations, their dissociation pathways were more complex. For those magic cations of P(+) 8k+1 observed previously, their dissociation pathways progressively change from the loss of P4 unit (for k = 3) to the loss of P8 unit (for k = 4, 5). A new dissociation pathway characterized by the loss of P10 unit was also indentified for larger cations of P(+) 8k+1 (6 ≤ k ≤ 8). Theoretical calculation also shows that, for cations of P(+) 2m+1 (4 ≤ m ≤ 10), the dissociation channel characterized by the loss of P4 unit is more energetically favorable than other dissociation channels, which is in good agreement with the experimental results.

Laser ablation synthesis of new gold phosphides using red phosphorus and nanogold as precursors. Laser desorption ionisation time-of-flight mass spectrometry

Gold phosphides show unique optical or semiconductor properties and there are extensive high technology applications, e.g. in laser diodes, etc. In spite of the various AuP structures known, the search for new materials is wide. Laser ablation synthesis is a promising screening and synthetic method. Generation of gold phosphides via laser ablation of red phosphorus and nanogold mixtures was studied using laser desorption ionisation time-of-flight mass spectrometry (LDI TOFMS). Gold clusters Au(m)(+) (m = 1 to ~35) were observed with a difference of one gold atom and their intensities were in decreasing order with respect to m. For P(n)(+) (n = 2 to ~111) clusters, the intensities of odd-numbered phosphorus clusters are much higher than those for even-numbered phosphorus clusters. During ablation of P-nanogold mixtures, clusters Au(m)(+) (m = 1-12), P(n)(+) (n = 2-7, 9, 11, 13-33, 35-95 (odd numbers)), AuP(n)(+) (n = 1, 2-88 (even numbers)), Au(2)P(n)(+) (n = 1-7, 14-16, 21-51 (odd numbers)), Au(3)P(n)(+) (n = 1-6, 8, 9, 14), Au(4)P(n)(+) (n = 1-9, 14-16), Au(5)P(n)(+) (n = 1-6, 14, 16), Au(6)P(n)(+) (n = 1-6), Au(7)P(n)(+) (n = 1-7), Au(8)P(n)(+) (n = 1-6, 8), Au(9)P(n)(+) (n = 1-10), Au(10)P(n)(+) (n = 1-8, 15), Au(11)P(n)(+) (n = 1-6), and Au(12)P(n)(+) (n = 1, 2, 4) were detected in positive ion mode. In negative ion mode, Au(m)(-) (m = 1-5), P(n)(-) (n = 2, 3, 5-11, 13-19, 21-35, 39, 41, 47, 49, 55 (odd numbers)), AuP(n)(-) (n = 4-6, 8-26, 30-36 (even numbers), 48), Au(2)P(n)(-) (n = 2-5, 8, 11, 13, 15, 17), A(3) P(n)(-) (n = 6-11, 32), Au(4)P(n)(-) (n = 1, 2, 4, 6, 10), Au(6)P(5)(-), and Au(7)P(8)(-) clusters were observed. In both modes, phosphorus-rich Au(m)P(n) clusters prevailed. The first experimental evidence for formation of AuP(60) and gold-covered phosphorus Au(12)P(n) (n = 1, 2, 4) clusters is given. The new gold phosphides generated might inspire synthesis of new Au-P materials with specific properties.

Finding stable minima using a nudged-elastic-band-based optimization scheme

Optimization is essential in many scientific and economical areas, but it is often too complex to be tackled by simple straightforward calculations or by trial and error. Two well-known methods to find low-lying minima in such complex systems are simulated annealing and the genetic algorithm. In these methods artificial fluctuations control the probability of the system to overcome a local minimum having a certain depth. Here we present a complementary scheme that is based on the nudged-elastic-band method ordinarily used to find saddle points and we apply the scheme to find the most stable isomers of the phosphorus P(4), P(8) molecules and the corresponding molecules of As(n), Sb(n), and Bi(n) (n = 4,8) in the framework of the density functional theory. In the case of n = 8 we have found stable and metastable configurations, some of which are new and have similar energies. As a by-product we obtained an upper bound for the energy barriers between these configurations.

Laser ablation synthesis of new phosphorus nitride clusters from α-P3N5 via Laser Desorption Ionization and Matrix Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry

Phosphorus nitride clusters generated during Laser Desorption Ionization (LDI) and Matrix-Assisted Laser Desorption Ionization (MALDI) of solid P(3) N(5) were analyzed via Time-of-Flight Mass Spectrometry (TOF MS). The LDI TOF mass spectra show the formation of series of clusters: P(m)N(n)(+) {(m=1; n=8-11), (m=4; n=3-4), (m=5; n=1-5), (m=6; n=1-3, 5-8), (m=2-7; n=1), (m=5-10; n=2), (m=4-6; n=3), (m=4,5; n=4), (m=5,6; n=5)}, and P(m)N(n)(-) (m=4,5; n=1). Using 3-hydroxypicolinic acid (HPA) as a matrix the P(m)N(n)(+) species (m=1-4, 6, 8) with a high nitrogen content (n=4, 5, 8, 10-12, 20) were identified. The formation of a N(6)(-) cluster was also detected using a C(60) matrix. Under various conditions singly charged P(m)(+) (m=2-7, 9, 13), P(m)(-) (m=3-11, 13, 15, 17), N(n)(+) (n=5, 9, 10, 12, 13), and N(n)(-) (n=6, 10-15) clusters were identified in the mass spectra. Such high nitrogen content clusters (up to N(15)(-)) generated by laser desorption from a solid material are described for the first time. The stoichiometry of the P(m)N(n) clusters was determined via isotopic envelope analysis and computer modelling. The composition of the clusters with respect to the crystalline structure of α-P(3)N(5) is discussed.

Parity Alternation of Ground-State Pn- and Pn+ (n = 3−15) Phosphorus Clusters

The ground-state structures of neutral, cationic, and anionic phosphorus clusters P(n), P(n)(+), and P(n)(-) (n = 3-15) have been calculated using the B3LYP/6-311+G* density functional method. The P(n)(+) and P(n)(-) (n = 3-15) clusters with odd n were found to be more stable than those with even n, and we provide a satisfactory explanation for such trends based on concepts of energy difference, ionization potential, electron affinity, and incremental binding energy. The result of odd/even alternations is in good accord with the relative intensities of cationic and anionic phosphorus clusters observed in mass spectrometric studies.

Structure and bonding in the isoelectronic series CnHnP5−n+: is phosphorus a carbon copy?

The relative stabilities of different isomers of the isoelectronic series C(n)H(n)P(5-n)(+) have been investigated using G3X theory. The results indicate that all species containing one or more phosphorus atom adopt a three-dimensional nido geometry, in marked contrast to the planar structure favoured by the all-carbon analogue. Within isomeric nido clusters, a strong correlation between total energy and the nucleus-independent chemical shift (NICS) indicates that three-dimensional aromaticity plays a significant role in determining the stability of the cluster. In the context of these nido clusters, the extent to which phosphorus is a carbon copy proves to be highly dependent on the global electronic environment. The first isolobal substitution of CH by P causes a complete switch from localised to delocalised bonding, accompanied by a transition from a two- to a three-dimensional structure, with the phosphorus atom showing a strong preference for the unique apical site. In contrast, further increasing the phosphorus content causes no further change in structure or bonding, suggesting that, at the basal sites, phosphorus is a rather better carbon copy. The low-energy pathways for interconversion of apical and basal atoms previously identified in C(2)H(2)P(3)(+) prove to be a general feature of all members of the series.