Quantum chemical studies on high-valent metal nitrido derivatives of Keggin-type polyoxometalates ([PW11O39{M(VI)N}]4- (M = Ru, Os, Re)): M(VI)-N bonding and electronic structures.

High-valent M(VI)N (M = Ru, Os) species are important reagents in nitrogen transfer reactions; the unique withdrawing properties of polyoxometalate (POMs) ligands would possibly modify the reactivity of the M(VI)N functional group. In the present paper, density functional theory (DFT) and natural bond orbital (NBO) analysis have been employed to calculate electronic structures, M(VI)-N bonding, and redox properties of high-valent metal nitrido derivatives of Keggin-type POMs, PW(11)O(39) {M(VI)N} (M = Ru, Os, Re). Our calculations show that PW(11)O(39){RuN} possesses stronger antibonding interaction between metal and nitrogen atoms compared with anions PW(11)O(39){OsN} and PW(11)O(39){ReN}. A large increase in the Ru-N bond length of anion PW(11)O(39){RuN} in the excited states has been found; the effective order and composition of the molecular orbital in anion PW(11)O(39){RuN} is a key factor in determination of the increase of the Ru-N bond length in the excited states. The substitution effects of central tetrahedron heteroatoms (XO(4), X = Al, Si, P, As) in anions XW(11)O(39){RuN} affect the relative energy of the LUMO; the relevant orbital energy increases in the order Al(III) < Si(IV) < P(V) approximately As(V). The RuN unit is the reduced center. NBO analysis of the extent of the bonding interaction between the ruthenium and the nitrogen centers in PW(11)O(39){Ru(VI)N} shows that the Ru-N bond possesses a covalent feature and displays triple-, double-, and single-bond character when moving along the change of spin state ((1)1 --> (3)1 --> (5)1).