Synthesis, characterization and thermal properties of trimetallic N3–CrCr⋯M–N3 azide complexes with M = Cr, Mn, Fe, and Co

Abstract

We report here two novel synthetic pathways toward the preparation of a family of trimetallic diazide compounds of the type Cr(2)M(dpa)(4)(N(3))(2), with M = Cr (10), Mn (4), Fe (5), and Co (11). Reaction of either Cr(2)M(dpa)(4)(OTf)(2) (for M = Mn and Fe) or [Cr(2)M(dpa)(4)(MeCN)(2)](PF(6))(2) (for M = Cr and Co) with sodium azide in methanol leads to the formation of the corresponding diazide compounds, and single crystal X-ray diffraction measurements confirm the predicted structures. Compounds 4, 5, and 10 are all high-spin compounds, but 11 is a spin-crossover compound exhibiting low-spin behavior at low temperatures (~100 K). Thermolytic characterization by DSC and TGA reveals an exothermic reaction corresponding to the loss of two dinitrogen molecules from compounds 5, 10, and 11. Further characterization by solution NMR measurements and cyclic voltammetry are also presented.

Solution structure of a pentachromium(ii) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

“…A reliable, Pd-free synthetic route has been developed to prepare H 2 tpda from 2,6-diaminopyridine and 2-fluoropyridine, with yield (90%) largely surpassing that of the best published methods. [43][44][45][46] 26 In these complexes of dpa − , a symmetric (D 4 ) structure would afford four inequivalent protons, while an unsymmetric (C 4 ) structure would contain eight inequivalent protons. The authors argued that a symmetric structure is most probably adopted over the timescale of NMR experiment, with one signal paramagnetically shifted and broadened beyond detection (based on our results, the signal from ortho-pyridyl protons).…”

“…24 However, the central metal ion lies in a very shallow potential energy surface and distortion of the symmetric structure is an energetically facile process, thereby explaining the structural versatility of trichromium(II) strings. 18,25,26 In pentachromium(II) EMACs, as well as in their Cr 7 and Cr 9 congeners, 27,28 application of the "splitatom" model results in a much more pronounced structural asymmetry, with d < = 1.86-2.03 Å, d > = 2.58-2.66 Å and Δd ∼ 0.7 Å in solvatomorphs of 2 at −60°C. 19,20 These complexes seemingly feature formally quadruply-bonded Cr 2 4+ units plus one terminal high-spin (S = 2) chromium(II) center, that in 2 exhibits a directionally-bistable magnetic moment and is at the origin of the observed SMM behaviour.…”

Metal–metal multiple bonding in C3-symmetric bimetallic complexes of the first row transition metals

“…This review is meant to cover and highlight recent achievements in these areas. There have been a number of other substantial contributions to the area of metal-metal multiple bonding involving first row transition metals, including polynuclear cluster compounds, [47][48][49][50][51] complexes featuring linear trimetallic chains, [52][53][54][55][56] and low coordinate bimetallic complexes having C 2 symmetry, 12,[57][58][59][60][61][62][63][64][65][66] but these topics are outside the scope of this review. It is also important to note that metal-metal bonding can be described using a molecular orbital approach or a valence bond approach in which interactions are described as antiferromagnetic and ferromagnetic interactions.…”

Theory, synthesis and reactivity of quintuple bonded complexes

“…Except 19, all the other Mn-Cr heterodinuclear complexes having the metal-metal interactions are very weak with bond distances longer than 2.68 Å. 71,72 The type IV configuration…”