page_title: Phosphaethynolate
section_title: Varying X
hierarchical_section_title: Phosphaethynolate / Other analogues of PCO / Varying X
caption_attribution_description: English: A contour plot depict the laplacian electron density of the PCO anion.
context_page_description: The phosphaethynolate anion is the phosphorus-containing analogue of the cyanate anion with the chemical formula [PCO]⁻ or [OCP]⁻. The anion has a linear geometry and is commonly isolated as a salt. When used as a ligand, the phosphaethynolate anion is ambidentate in nature meaning it forms complexes by coordinating via either the phosphorus or oxygen atoms. This versatile character of the anion has allowed it to be incorporated into many transition metal and actinide complexes but now the focus of the research around phosphaethynolate has turned to utilising the anion as a synthetic building block to organophosphanes.
context_section_description: The simplest analogue that can be formed as ‘X’ is varied is PCS⁻. This anion was first isolated by Becker et al. by reacting the phosphaethynolate anion with carbon disulphide. Unlike PCO, PCS shows ambidentate nucleophilic tendencies towards the W(0) complex mentioned above.
  This is the result of a reduced difference in electronegativity between E and X thus neither atom offers a substantial advantage over the other in terms of providing ionic contributions to bonding. As a result, the average electron density in PCS is spread over the entire anion (see Figure 8) whereas in PCO, most electron density is localised on the phosphorus atom (see Figure 7) as this is the atom which bonds to form the thermodynamically favourable product.
caption: Figure 7: Contour plot of the laplacian electron density of the PCO anion. Graph plotted in Multiwfn using the results of AIMS analysis from Molden and GAMESS.[7] From top to bottom, the atoms are O, C and P.
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