Characterization and Electronic Structures of Six-Coordinate Trigonal-Prismatic Complexes

Abstract

2956~i m )~, a and Ni(N-isopr0pyl-3-methylsim)~] ; l8 for difference in coordination configuration is ignored, as tetrahedrally coordinated Ni(I1) the bite is 2.84 A in Figure 3, the acac bite distance of 2.584 A obtained [Ni(N-i~opropylsim)2];'~ and for octahedrally coordi-by extrapolation of r / Q to 0 in Figure 3 is in fair agreenated Ni (I1) the bite is 2.91 [Ni(~a1)2.2H~O],~~ 2.91 ment with the salicylic acid bite distance of 2.620 A [Ni(acac)z.2H20],4 and 3.05 A [Ni(acac)~].~~ If the around the hydrogen i o r a s Acknowledgment. This work was supported in (42) Abstract:The physical properties of the trigcis-stilbenedithiolato) complexes of Mo, W, and Re are described in detail. The three neutral M(SZC2Ph2)3 complexes exhibit MSe trigonal-prismatic coordination in the solid state and in solution. The V and Cr complexes in this series are isomorphous with the Mo complex and thus very probably are also trigonal prismatic in the solid state. The syntheses and properties of the tris(toluene-3,4dithiolato) and tris(benzene-l,2-dithiolato) complexes of Mo, W, and Re are reported. In particular, those properties which have been found to be characteristic of trigonal-prismatic coordination are discussed in detail. It is concluded that at least 12 different well-authenticated complexes, spanning five metals and four different ligands, exhibit a six-coordinate trigonal-prismatic structure. In addition, the existence of numerous other complexes, related to the above by reversible one-electron transfers, is established by polarography. The electronic spectra of all the neutral complexes are discussed in terms of a molecular orbital model of energy levels. The molecular orbital bonding scheme is found to be consistent with the considerable electronic spectral and polarographic data. ix-coordinate complexes of bidentate, unsaturated S sulfur-donor ligands have been the subject of extensive current investigations. 2-7 These studies have recently assumed a new and quite fundamental significance in transition metal chemistry. The structure of Re(SzC2Ph& (I) has been solved by X-ray diffraction analysiss and has been found to contain a near-perfect trigonal-prismatic array of sulfur-donor atoms. that SGPhZ forms bis planar complexes with Os, Ru, Cr, Mo, W, Re, and V. This has since been shown to be in error as these are all tris complexes. See ref 5, 6, and G. N. Schrauzer, H. W. Finck, and V. Mayweg, Angew. Chem., 76, 715 (1964). (b) The Mo(tdt)8 complex has apparently been prepared previously by T. W. Gilbert, Jr., and E. B. Sandell, J. A m . Chem. Soc., 82, 1087 (1960). However, an accurate analysis was not obtained and the compound was thus not fully characterized. (8) R. Eisenberg and J. A. Ibers, ibid., 87, 3776 (1965); Inorg. Chem., 5, 411 (1966). 91 109.(9) This is the first reported trigonal-prismatic molecular complex. Trigonal-prismatic coordination was first reported [R. G. Dickinson and L. Pauling, J. Am. Chem. Soc., 45, 1466 (1923)J for the infinitely extended lattices of molybdenite (MoSZ) and tungstite (WSz). ...

Trigonal prismatic versus octahedral coordination geometry of transition metal dithiolates: Comparison between saturated and unsaturated early transition metal tris(1,2-dithiolate) complexes

“…n,, 4e-stabilize the e' metal orbitals and hence lead to TP geometry. This is not a new result and had been considered by previous workers in the field (2,8,13). Nevertheless, it provides a natural link to other "even" type unsaturated ligands that present a symmetrical empty n-acceptor orbital to the central metal atom and properly account for the TP geometry observed in tris(buta-1,3-diene)molybdenum (29), tris(ortho-xyly1)tungsten (30), and tris(methylviny1ketone)tungsten (3 1 &P importance of n back-bonding for the observed TP rather than octahedral geometry about the metal atom in tris(buta-1,3-diene)Mo/W.…”

“…Also shown in the scheme is the oxidized, dithioketone formulation of the unsaturated ligand. Under this formulation, which is the more traditional view with these "dithiolene" type ligands (7, 8,13), the ligand presents a low-lying symmetric n-acceptor orbital (3nv) to the metal. Although the n-donor picture is more appropriate with the anionic complexes of the early transition metals since, as detailed elsewhere (1 1, 12, 15), these complexes contain the more reduced form of the unsaturated 1 ,Z-dithiolates, it is clear that to achieve a unified picture for the possible importance of n bonding in stabilizing the TP geometry with different 1,2-unsaturated ligands the n-acceptor extreme will also have to be invoked.…”

“…In 1965 the first observation of a discrete TP complex, Re(l ,2,-S2C2Ph2)3 (3), rekindled interest in TP geometry and since then a host of factors, such as (a) ligand constraint (4,5), (b) ligand field stabilization energy (2,4,6), (c) interdonor atom bonding (3,(7)(8)(9), (d) proper matching of ligand and metal orbital energies (1,2,(10)(11)(12), (e) the symmetry of ligand n orbitals (2,8,13), and (f) the overall charge of the complex, have been suggested as important factors influencing the formation of TP, octahedral, or intermediate geometries. From experimental work of Holm and co-workers (4) and Eatough et al (14) and theoretical work of Holm (4), Kepert ( 3 , and Wentworth (6) it appears that the two most important factors involved are probably the ligand constraint (provided by cage type 'present address: Phillips Petroleum Co., 96-G PRC, Bartlesville, OK 74004, U.S.A.…”

The Electronic Structure and Spectroscopy of Metallo‐Dithiolene Complexes

“…The seminal studies of Gray and co-workers (280,406), and Schrauzer and co-workers (407) represent the earliest attempts to employ MO theory toward understanding the electronic absorption spectra of six-coordinate TP metallo-tris(dithiolenes). However, only the former researchers made concrete attempts to understand the key electronic structure factors that stabilize the TP geometry over the more common octahedral arrangement.…”

“…A considerable amount of experimental evidence over the last 40 years has pointed to the fact that dithiolenes are highly noninnocent ligands (20,86,110,113,(280)(281)(282). That is, they may be viewed in a valence bond description as existing somewhere between the extremes of neutral (dithione/dithiete) and dianionic (dithiolate) forms (Fig.…”