Abstract

M.L.Sehgal¹, Amit Aggarwal² and Irshad Ahmad³

DOI : http://dx.doi.org/10.13005/ojc/330201

DFT implemented in ADF 2012.01 was used to know about the relative spatial displacements of three/four metals and the surrounding12 terminal and bridging CO groups in 5 poly-nuclear carbonyls:[M₃(CO)₁₂],(M=Ru,Os),[Ir₄(CO)₁₂],[Fe₃(CO)₁₂] and  [Rh₄(CO)₁₂]. After optimization, the software was first run using the “NMR Program” with Single Point,  Default, None, Collinear, Nosym using TZP or TZ2P Basis sets leaving Unrestricted command  blank to obtain the Shielding Constants (σM ,σ ¹³C,σ ¹⁷O), the Chemical Shifts    (δ M, δ¹³C, δ¹⁷O), 2 diamagnetic and 4 paramagnetic contributing terms in the  σ values of  constituents.The k and j values of constituents were obtained from the same program by using a new Input File.There after, the software was run with Frequencies and Raman full to obtain frequencies of the normal modes of all the (3n-6) Fundamental vibration bands of the carbonyls. All the metals in the above named first three carbonyls were spatially equivalent while in the latter two carbonyls,all the metals were not equivalent.But no where, the two metals  or any two COs were found to be magnetically equivalent.Excepting Ir₄(CO)₁₂ where all the12 CO groups were spatially equivalent,in other four carbonyls, CO groups were  found to be two or more types spatially.The first metal and the responding spatially equivalent other metal/s possessed same k and j values. For CO groups attached to one metal and spatially equivalent CO groups attached to other spatially equivalent metal/s, k and j values of ¹³C nuclei possessed the same values.A perturbing metal and spatially equivalent responding metal/s along with spatially equivalent CO groups had same k and j values respectively. The study was important in four ways. Firstly,using these parameters, we could calculate quite a more number of parameters such as Effective Spin Hamiltonian (H^Spin) of the metals and ¹³C nuclei,Coordination Shifts (Δ_δ¹³C,Δ_δ¹⁷O),atomic electron valence density(integrated)/ L value of ¹⁷O and charges on both the ¹⁷O and metals  along with spatial displacements/stereochemical equivalencesof constituents. Secondly, we could correlate these NMR parameters with their reported IR/Raman results which lent credence to their π–acid character.Thirdly,we classified their fundamental vibration bands types into four types.Fourthly, we could arrive at some optimization and thermal  parameters of carbonyls.

Chemical Shift; Shielding Tensor; Paramagnetic Tensor; Effective Spin Hamiltonian; Magnetic Equivalence

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