Crystal-to-crystal transformation upon dehydration of a copper(II) 2,2':6',2''-terpyridine complex

The reaction of 2,2':6',2''-terpyridine (terpy) with CuCl(2) in the presence of sodium sulfite led to the synthesis of the ionic complex aquachlorido(2,2':6',2''-terpyridyl-κ(3)N,N',N'')copper(II) chlorido(dithionato-κO)(2,2':6',2''-terpyridyl-κ(3)N,N',N'')cuprate(II) dihydrate, [CuCl(C(15)H(11)N(3))(H(2)O)][CuCl(S(2)O(6))(C(15)H(11)N(3))]·2H(2)O, (I), and the in situ synthesis of the S(2)O(6)(2-) dianion. Compound (I) is composed of a [CuCl(terpy)(H(2)O)](+) cation, a [Cu(S(2)O(6))(terpy)](-) anion and two solvent water molecules. Thermogravimetric analysis indicated the loss of two water molecules at ca 363 K, and at 433 K the weight loss indicated a total loss of 2.5 water molecules. The crystal structure analysis of the resulting pale-green dried crystals, μ-dithionato-κ(2)O:O'-bis[chlorido(2,2':6',2''-terpyridyl-κ(3)N,N',N'')copper(II)] monohydrate, [Cu(2)Cl(2)(S(2)O(6))(C(15)H(11)N(3))(2)]·H(2)O, (II), revealed a net loss of 1.5 water molecules and the formation of a binuclear complex with two [CuCl(terpy)](+) cations bridged by a dithionate dianion. The crystal-to-crystal transformation involved an effective reduction in the unit-cell volume of ca 7.6%. In (I), the ions are linked by O-H...O hydrogen bonds involving the coordinated and solvent water molecules and O atoms of the dithionate unit, to form ribbon-like polymer chains propagating in [100]. These chains are linked by Cu...Cl interactions [3.2626 (7) Å in the cation and 3.3492 (7) Å in the anion] centred about inversion centres, to form two-dimensional networks lying in and parallel to (0-11). In (II), symmetry-related molecules are linked by O-H...O hydrogen bonds involving the partially occupied disordered water molecule and an O atom of the bridging thiosulfite anion, to form ribbon-like polymer chains propagating in [100]. These chains are also linked by Cu...Cl interactions [3.3765 (12) Å] centred about inversion centres to form similar two-dimensional networks to (I) lying in and parallel to (0-22), crosslinked into three dimensions by C-H...O=S and C-H...O(water) interactions.