Dithiosquarate (dtsq) complexes of nickel(II). Syntheses and crystal structures of [Ni(phen)2(1,2-dtsq)]·3.5H2O, [Ni(phen)2(1,3-dtsq)] and [Ni(tren)(1,2-dtsq)] [phen=1,10-phenanthroline; tren=tris(2-aminoethyl)amine]

The new nickel(II) complexes [Ni(phen)2(1,2-dtsq)]·3.5H2O (1), [Ni(phen)2(1,3-dtsq)] (2) and [Ni(tren)(1,2-dtsq)] (3) [1,2-dtsq=dianion of 3,4-dimercapto-3-cyclobutene-1,2-dione, 1,3-dtsq=dianion of 3-hydroxy-4-mercapto-2-thioxo-3-cyclobuten-1-one, phen=1,10-phenanthroline and tren=tris(2-aminoethyl)amine] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures are made up of neutral [Ni(phen)2(1,n-dtsq)] [1 (n=2) and 2n=3)] and [Ni(tren)(1,2-dtsq)] (3) mononuclear units. The nickel atom is six-coordinated in all three cases: four nitrogen atoms from two bidentate phen (1 and 2) or a tetradentate tren (3) groups and either two sulfur (1 and 3) or a sulfur and an oxygen atoms (2) atoms from the dithiosquarate (dtsq) ligands form a distorted octahedron around the metal atom. The NiN(phen) bond lengths [2.082(5)–2.103(5) Å for 1 and 2.075(8)–2.124(9) Å for 2] are very close to that of NiN(tren) [2.088(2)–2.140(2) Å for 3]. The NiS bond distances are 2.4598(15) and 2.4817(15) Å for 1, 2.497(3) Å for 2 and 2.4362(6) and 2.6446(7) Å for 3. The values of the angle subtended at the metal atom by the 1,2-dtsq [91.06(4) (1) and 89.61(2)° (3)] and 1,3-dtsq [88.4(2)° (2)] ligands are very close to the ideal value of 90° in spite of their asymmetric bidentate coordination. The influence of the number and position of sulfur atoms of these ligands on their coordination modes is analyzed and discussed in the light of the available structural data.