Sixteen crystal structures have been determined for the Co3(dpa)(4)Cl2 (1) molecule in the following five crystalline solvates: 1.0.85(C2H5)(2)O.0.15CH2Cl2 (at 120, 213, 296 K); 1.C(4)H(8)O (at 120, 295 K); 1.C(6)H(6) (at 170, 213, 260, 316 K); 1.C(6)H(12) (at 120, 213, 295 K); and 1.1.75C(7)H(8).0.5C(6)H(14) (at 90, 110, 170, 298 K). For 1.0.85(C(2)H(5))(2)O.0.15CH2Cl2 the molecule of 1 is almost symmetrical at 120 K (Co-Co distances of 2.3191(3) and 2.3304(3) A) and remains so at 296 K (2.2320(3) and 2.3667(4) A). For 1.C(4)H(8)O the Co(3) chain is precisely symmetric at both 120 and 295 K though the Co-Co distances increase from 2.3111(4) to 2.3484(4) A as the temperature rises. Compound 1.C(6)H(6) is isomorphous with 1.C(4)H(8)O at 213 and 295 K and has rigorously symmetrical molecules at these two temperatures. Between 213 and 120 K the space group changes from Pccn to P2(1)/c, so that a symmetrical arrangement is no longer required and the two Co-Co distances then differ slightly (by 0.013 A). For 1.C(6)H(6) there is a phase change between 316 K (Pca2(1)) and 260 K (Pna2(1)). At all four temperatures, however, the molecule is almost symmetrical, with the two independent Co-Co distances never differing by more than 0.026 A. 1.1.75C(7)H(8).0.5C(6)H(14) contains, at all temperatures between 90 and 298 K, two crystallographically independent molecules, each of which is distinctly unsymmetrical at 298 K (Co-Co distances of 2.312(2) and 2.442(2) A for one and 2.310(2) and 2.471(2) for the other). In the first of these the distances converge to a much smaller separation (0.056 A) at 90 K while in the second the difference decreases to only 0.006 A at 90 K. Magnetic susceptibility measurements from 1.8 to 350 K indicate in each case that a gradual spin crossover, from a doublet to a quartet state, occurs over this temperature range.

The anion of 2,6-di(phenylimino)piperidine (DPhIP) has been found to support linear chains of three metal atoms. Three new compounds, [Cr3(DPhIP)4Cl]Cl.(1).5CH2Cl2.0.5H2O (1.1.5CH2Cl2.0.5H2O), [Cr3(DPhIP)4(CH3CN)]- (PF6)2.H2O.4CH3CN (2.H2O.4CH3CN), and [Cr3(DPhIP)4(F)(CH3CN)](BF4)2.5CH3CN (3.5CH3CN), have been synthesized and characterized by X-ray crystallography. Compound 1 has a linear chain of three chromium atoms arranged in an unsymmetrical fashion, with two of them forming a quadruply bonded unit (Cr-Cr distance 1.932(2) A) and the third being a non-metal-metal-bound 5-coordinate unit (Cr...Cr distance 2.659(2) A). The fifth coordination site is occupied by a chloride ion, and another chloride ion is located in the interstices of the crystal. The trimetal unit in compound 2 is structurally similar to that in compound 1 except that the axial ligand in 2 is a CH3CN molecule. Compound 3 is an oxidation product prepared by reaction of 1 with AgBF4. Here, a square pyramidal CrIII unit, FCrN4, and a Cr-Cr quadruply bonded (Cr-Cr distance 1.968(2) A) unit, with an axially coordinated acetonitrile molecule, form the trichromium chain. The CrIII...CrII separation of 2.594(2) A in 3 is too long to be considered a bonding interaction.

The quadruply bonded compound Mo2(DpyF)4 (1), where DpyF- is the anion of N,N'-di(2-pyridyl)formamidine, has been prepared by ligand substitution reactions of Mo2(OOCCF3)4 and either the neutral ligand, HDpyF, at ambient temperature or its lithium salt, LiDpyF, under refluxing conditions. An X-ray structural analysis shows that 1 has a paddlewheel structure with a [symbol: see text] distance of 2.1108(6) A. Reaction of 1 with CoCl2 in methanol produces the paramagnetic compound [Mo2Co(DpyF)4][CoCl4].2MeOH (2). The Co(II) atom in the cation [Mo2Co(DpyF)4]2+ resides on a low-spin hexacoordinate environment (S = 1/2) with a Co...Mo separation of 2.979(6) A, suggesting there is no direct bonding interaction between the Co and Mo atoms. The Mo-Mo distance of 2.1096(5) A is similar to that in 1. Reaction of 1 and CuCl in methanol yields [Mo2Cu4(DpyF)4Cl2][CuCl2]2.2MeOHxEt2O (3). In the cation there are two copper atoms on each side of the Mo2 core. Each is coordinated to two pyridyl nitrogen atoms of the cis DpyF- ligands and loosely bridged to the other by a chloride ion. As a result, the Cu(I) atoms are not aligned with the Mo2 unit. The Cu to Mo separations are in the range 3.003(1)-3.015(1) A, and the Mo-Mo distance of 2.127(1) A is comparable to those in 1 and 2.