Dipotassium salt of 3-hydroxy-4-mercapto-2-thioxo-3-cyclobuten-1-one dihydrate (potassium 1,3-dithiosquarate dihydrate), K2[C4O2S2].2H2O, at 140 K

Coordination Modes of the 1,3-Dithiosquarate (1,3-dtsq) Ligand. Syntheses, Crystal Structures, and Magnetic Properties of [Ni(tren)(1,3-dtsq)(H2O)] and [Ni2(tren)2(1,3-dtsq)](ClO4)2 [tren = Tris(2-aminoethyl)amine]

“…This allows for a S‚‚‚O(1) bite distance in this complex of 3.270(3) Å, while the S‚‚‚O(1) i distance is 3.754(3) Å. By comparison the S(2)‚‚‚O(1) distance in 1 (3.530-(1) Å), which is not affected by coordination, is also close to the S‚‚‚O distances in the squarate dianion in K 2 (1,3-dtsq)‚-2H 2 O (3.554(1) and 3.515(1) Å) 20. Furthermore the Ni-S-C(7) bond angle in 2 is only 90.0(1)°, while the corresponding angle in 1 is 114.31(7)°.…”

“…The 1,3-dithiosquarato ligand is monodentately coordinated through one of the sulfur atoms. The coordination does not introduce a significant difference in the two the S−C bond lengths (1.665(2) and 1.663(2) Å); by comparison, in the uncomplexed 1,3-dtsq dianion the corresponding bonds are slightly longer (1.672(2) Å) . The external angles at C(7) are markedly different, S(1)−C(7)−C(8) = 131.5(1)° and S(1)−C(7)−C(10) = 139.0(2)°; this distortion is probably related to the accommodation of an intramolecular hydrogen bond between O(2) of the dtsq group and the coordinated water molecule (O(2)···O(3) = 2.733(2) Å).…”

“…The coordination does not introduce a significant difference in the two the S-C bond lengths (1.665(2) and 1.663(2) Å); by comparison, in the uncomplexed 1,3-dtsq dianion the corresponding bonds are slightly longer (1.672(2) Å). 20 The external angles at C(7) are markedly different, S(1)-C(7)-C(8) ) 131.5(1)°and S(1)-C(7)-C(10) ) 139.0(2)°; this distortion is probably related to the accommodation of an intramolecular hydrogen bond between O(2) of the dtsq group and the coordinated water molecule (O(2)‚‚‚O(3) ) 2.733(2) Å). The four 1,3-dtsq carbon atoms are coplanar within the limit of error, but the sulfur atoms deviate significantly from the plane (Table S10).…”

“…The chelating mode may at a first sight seem surprising considering the fact that a corresponding mode is not found for squarato complexes of 3d metal ions due to the large bite parameter of the latter ligand. 8b,11 The S‚‚‚O bite distance in the uncomplexed 1,3-dtsq dianion is 3.53 Å (average value), 20 and considering a complex with a S-M-O angle of 90°would lead to M-X bond distances of approximately 2.50 Å. In the present case (2) the S‚‚‚O bite distance is reduced to 3.270(3) Å through a reduction of the chelate endo S(O)-C-C angles from the idealized 135°to 127.2 and 129.5°, respectively.…”

“…However, the reduction of the bite parameter (bite distance/M−O(squarato) bond length) 8b,11 by using heavier metal ions (alkaline- and rare-earth cations) 12,13 renders possible these coordination modes as shown by X-ray diffraction studies. The replacement of two adjacent oxygen atoms of squarate by a larger substituent such as sulfur also reduces the bite parameter, and the resulting 1,2-dithiosquarate group is able to act as a chelating ligand through its two sulfur atoms to 3d and heavier metal ions. − If the substitution of squarate oxygen atoms by sulfur atoms is carried out on two nonadjacent positions, the resulting 1,3-dithiosquarate anion (dianion of 3-hydroxy-4-mercapto-2-thioxo-3-cyclobuten-1-one, hereafter noted 1,3-dtsq)could exhibit both chelating and bischelating coordination modes. To our knowledge, no crystallographic report concerning metal complexes with 1,3-dtsq has been published thus far.…”