Preparation, Structure, and Properties of the Arsenic-Containing Corner-Shared Double Cube [Mo6AsS8(H2O)18]8+:  Metal−Metal Bonding and a Classification of Different Cluster Types

For many years it has been known that the nine water molecules in [M(3)Q(4)(H(2)O)(9)](4+) cuboidal clusters (M = Mo, W; Q = S, Se) can be replaced by entering ligands, such as chloride or thiocyanate, and kinetic studies carried out mainly on the substitution of the first water molecule at each metal centre reveal that the reaction at the three metal centres occurs with statistical kinetics; that is, a single exponential with a rate constant corresponding to the reaction at the third centre is observed instead of the expected three-exponential kinetic trace. Such simplification of the kinetic equations requires the simultaneous fulfilment of two conditions: first that the three consecutive rate constants are in statistical ratio, and second that the metal centres behave as independent chromophores. The validity of those simplifications has been checked for the case of the reaction of [Mo(3)S(4)(H(2)O)(9)](4+) with Cl(-) by using DFT and TD-DFT theoretical calculations. The results of those calculations are in agreement with the available experimental information, which indicates that the H(2)O ligands trans to the μ-S undergo substitution much faster than those trans to the μ(3)-S. Moreover, the energy barriers for the substitution of the first water molecule at the three metal centres are close to each other, the differences being compatible with the small changes in the numerical values of the rate constants required for observation of statistical kinetics. TD-DFT calculations lead to calculated electronic spectra, which are in reasonable agreement with those experimentally measured, but the calculations do not indicate that the three metal centres behave as independent chromophores, although the mathematical conditions required for simplification of the kinetic traces to a single exponential are reasonably well fulfilled at certain wavelengths. A re-examination of the kinetics of the reaction by using global fitting procedures yields results, which are compatible with statistical kinetics, although an alternative interpretation in which substitution only occurs at a single metal centre under reversible conditions is also possible.

Section: Td-dft Calculationsmentioning

confidence: 80%

A DFT and TD‐DFT Approach to the Understanding of Statistical Kinetics in Substitution Reactions of M₃Q₄ (M=Mo, W; Q=S, Se) Cuboidal Clusters

Algarra

Fernández‐Trujillo

Basallote

2012

“…For example: As(S 2 CO i Pr) 3 2.305/2.978 Å,35 As(S 2 P{OMe} 2 ) 3 2.315/3.031 Å,36 As(S 2 CN n Bu 2 ) 3 2.347/2.875 Å37 and As(S 2 C‐ p ‐tol) 3 2.317/2.969 Å 38. The only previously reported example of an essentially regular AsS 6 species occurs when two {Mo 3 (μ 3 ‐S)(μ 2 ‐S) 3 (OH 2 ) 9 } clusters “sandwich” an As 3+ ion, coordinating by means of the di‐bridging sulphides, giving AsS bond lengths in the narrow range 2.434–2.489 Å (Scheme b) 39. A similar lack of distortion has already been noted in Levason's seleno–ether macrocycle complex 29.…”

Section: Discussionmentioning

confidence: 99%

Lower Main‐Group Element Complexes with a Soft Scorpionate Ligand: The Structural Influence of Stereochemically Active Lone Pairs

Dodds

Reglinski

Spicer

2006

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand, hydrotris(methimazolyl)borate (Tm(Me)) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm(Me). The indium(III) complexes took the form [In(kappa(3)-Tm(Me))(2)](+). This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(kappa(3)-Tm(Me))(kappa(1)-Tm(Me))X] (X = Br, I). An iodo-bridged species [Sb(kappa(3)-Tm(Me))I(mu(2)-I)](2), analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm(Me) results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO(3))(3) with NaTm(Me) results in a complex with a regular S(6) coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm(Me) complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm(Me) complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm(Me) to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.

“…Main group element chalcogenide dicubanes are explored for their non‐linear optical ([Sb 7 Ch 8 ] 5+ and [Sb 7 Ch 8 X 2 ] 3+ , Ch: chalcogen; X: halogen) [21–24] and catalytic (Sn 7 S 8 ) [25] properties. Many single and double cuboidal derivatives of molybdenum chalcogenides have been exploited to understand the metal‐metal bonding in different cluster types [26–30] . Double‐cubane type copper complexes with exogenous anions showed strong AFM coupling between Cu(II) centers with reduced magnetic moments as a result of magnetic exchange facilitated by their topology and connectivity [31–33] .…”

Section: Introductionmentioning

confidence: 99%

Solvothermal Synthesis of [Cr₇S₈(en)₈Cl₂]Cl₃ ⋅ 2H₂O with Magnetically Frustrated [Cr₇S₈]⁵⁺ Double‐Cubes**

Gamage

Clark

Yazback

et al. 2021

A novel transition metal chalcohalide [Cr7S8(en)8Cl2]Cl3 ⋅ 2H2O, with [Cr7S8]5+ dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant, θ=−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions between S=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)7=16384 microstates from seven Cr3+ centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to be J1=−21.4 cm−1 and J2=−30.2 cm−1, confirming competing AFM coupling between the shared Cr3+ center and the peripheral Cr3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J1=−20.0 cm−1 and J2=−21.0 cm−1, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr3+ ions as compared to the AFM exchange between the central and peripheral Cr3+ ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks.