Preparation and structure of the dimolybdenum(III) compound hexachlorotetrakis(triethylphosphine)dimolybdenum. An anomaly in metal-metal-bonded edge-sharing bioctahedral compounds

Abstract

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Anionic Halomolybdate(III) Chemistry. Tetrahydrofuran Loss from [MoX3Y(THF)2]-(X, Y = Cl, Br, I), Preparation and Properties of [Mo3X12]3-(X = Br, I), and Crystal Structure of the Edge-Sharing Trioctahedral [PPh4]3[Mo3I12]

“…) neutral 2-electron donor) mononuclear octahedral MoX 3 L 3 , [1][2][3][4][5][6][7][8][9][10][11] [MoX 4 L 2 ] -, 10,12-14 and [MoX 6 ] 3-, 15,16 dinuclear edge-sharing bioctahedral Mo 2 X 6 L 4 , [17][18][19][20][21][22][23][24] dinuclear face-sharing bioctahedral Mo 2 X 6 L 3 , 22,[25][26][27] [Mo 2 X 7 L 2 ] -, 28,29 and [Mo 2 X 9 ] 3-, [30][31][32][33] and the MoX 3 solids where one-third of the octahedral holes of the closepacked halide substructure are occupied by the metal atoms. 34,35 The occupied octahedral holes are arranged pairwise to give an infinite three-dimensional (for X ) Cl) and monodimensional (for X ) Br) {X 3/2 Mo(µ-X) 3 MoX 3/2 } ∞ structure with localized Mo-Mo bonds.…”

“…Coordination compounds of molybdenum(III) with ligands that do not possess strongly π-donating capabilities tend to adopt an octahedral coordination geometry. In the realm of molybdenum halide complexes, examples are (X = halide, L = neutral 2-electron donor) mononuclear octahedral MoX 3 L 3 , − [MoX 4 L 2 ] - , ,− and [MoX 6 ] 3- , , dinuclear edge-sharing bioctahedral Mo 2 X 6 L 4 , − dinuclear face-sharing bioctahedral Mo 2 X 6 L 3 , ,− [Mo 2 X 7 L 2 ] - , , and [Mo 2 X 9 ] 3- , − and the MoX 3 solids where one-third of the octahedral holes of the close-packed halide substructure are occupied by the metal atoms. , The occupied octahedral holes are arranged pairwise to give an infinite three-dimensional (for X = Cl) and monodimensional (for X = Br) {X 3/2 Mo(μ-X) 3 MoX 3/2 } ∞ structure with localized Mo−Mo bonds. When one considers the hypothetical process of breaking apart the infinite MoX 3 structure by stepwise adding X - ions, one should arrive directly, without breaking metal−metal bonds, at dinuclear [Mo 2 X 9 ] 3- units and then eventually to mononuclear [MoX 6 ] 3- .…”

Let's Not Forget About Electronic Correlation

“…The energetic balance between the two stabilizations must be very delicate for molybdenum. For the tungsten analogue mentioned above, i.e., W2Cl6(PEt3)4, 30 the presence of a metal-metal interaction (and no paramagnetism: for instance, sharp 31 P-NMR resonances can be observed, whereas no 31 P-NMR signal is observable for the Mo analogue) may be the result of the combined effect of the higher d-d overlap and lower pairing energies. Conversely, lower d-d overlap and higher pairing energies induce the formation of the nonbonded chromium analogue, Cr2Cl6(PEt3)4.…”