Xuejun Feng

Unligated dirhodium tetra(trifluoroacetate): preparation, crystal structure and electronic structure

Abstract The title compound, Rh2(O2CCF3)4, without any exogenous axial ligands, has been obtained in crystalline form by sublimation. Its crystal structure has been determined: space group P 1 with α = 5.2499(5), b = 8.491(2), c = 9.172(2) A , α = 88.80(2), β = 88.53(1), γ = 76.43(1)°, V = 397.3(1) A 3 , Z = 1 . The molecules are linked by axially ligating each other to form infinite chains. The Rh-Rh distance is 2.3813 (8) A. The volatility of Rh2(O2CCF3)4 should allow spectrospcopic study of the isolated molecules and therefore the electronic structure has been treated by the SCF-Xα-SW method. The level ordering and composition show significant differences from those of Rh2(O2CH)2, although in both molecules there is a strong Rh-Rh σ bond. Ionizatio potential have been estimated by the transition state method.

The use of CoCl2(amidine)2 compounds in the synthesis of tetragonal lantern dicobalt compounds: synthesis, structures and theoretical studies of Co2(DPhF)4 and the oxidized species [Co2(DPhBz)4]+ (DPhF = N,N′-diphenylformamidinate, DPhBz = N,N′-diphenylbenzamidinate)

Abstract CoCl2(PhNC(R)N(H)Ph)2 complexes (R = H and Ph) have been reacted with methyllithium to produce the corresponding lantern-type Co2(amidinato)4 compounds containing cobalt-cobalt bonds of order one. One of them, Co2(DPhBz)4(DPhBz = diphenylbenzamidinato), was oxidized by AgPF6 to yield [Co2(DPhBz)4](PF6·2.4CH2Cl2. Crystal data for Co2(DPhF)4(I) (DPhB = diphenylformamidinato) at 0°C are: monoclinic, space group C2/c, a = 13.927(3), b = 13.678(3), c = 22.855(5) A , β = 91.37(2)°, Z = 4 . For [Co2(DPhBz)4]- (PF6)·2.4CH2Cl2 (II) at −60°C: triclinic, space group P1, a = 13.838(4), b = 13.881(4), c = 19.62(1), A , α=89.7(1), β = 99.76(4), γ = 91.04(4)°, Z = 2 . The metal-to-metal distances are 2.3735(9) A for complex I and 2.322(2) and 2.332(2) A for two crystallographically independent molecules found in complex II. The latter are slightly longer than those found in the parent neutral molecule. The experimental cobalt-to-cobalt separations are in good agreement with those obtained from ab initio quantum chemical calculations.

Experimental and theoretical study of a paradigm Jahn-Teller molecule, all-trans-CrCl2(H2O)2(pyridine)2, and the related trans-CrCl2(pyridine)4·acetone

Abstract The first title molecule has been prepared from an aqueous solution of CrCl 2 and shown to have an all- trans , octahedral arrangement of ligands; the Jahn-Teller (J-T) effect manifests itself in elongation of the Crue5f8Cl bonds (2.7670(7) A) while the Crue5f8O (2.066(2) A) and Crue5f8N (2.127(2) A) bonds have ‘normal’ lengths. A theoretical study by the SCF-Xα method was carried out hoping to obtain a better understanding of this form of distortion and to gain insight into the nature of the forces involved. The CrCl 2 (H 2 O) 2 (py) 2 ( I ) molecule resides on an inversion center in a crystal belonging to the triclinic space group P 1 . At −50 °C, a = 6.248(2), b = 6.640(2), c = 8.506(3) A , α = 109.49(2), β = 100.84(2), γ = 100.31(2)°, V = 315.4(2) A 3 and Z = 1. An azeotropic distillation of the water molecules produces CrCl 2 (py) 4 ·acetone ( II ). Compound II crystallizes in the hexagonal space group P 6 5 22. At −60°C, a = 8.9873(7), c = 51.223(7) A , V = 3583.1(6) A 3 and Z = 6.