Dinuclear RhII-Phthalocyaninates with a Rh-Rh Single Bond: X-ray Crystal Structure of Di(pyridinephthalocyaninato(2-)rhodium(II))

Abstract

Red, diamagnetic di(phthalocyaninato(2-)rhodium(II)), [( Rhpc 2−)2] is prepared by thermal decomposition of acidophthalocyaninatorhodium(III) or di(acido)phthalocyaninatorhodates(III) in inert, high boiling solvents or under reduced pressure at T < 350° C . It is insoluble in most common solvents except pyridine ( py ), yielding red, diamagnetic di(pyridinephthalocyaninato(2-)rhodium(II)), [{ Rh ( py ) pc 2−}2]. This crystallizes as benzene solvate in the cubic space group Ia-3 (no. 206) (a = 35.960(7) Å) with Z = 24. The Rh - Rh distance (d( Rh - Rh ) = 2.741(2) Å) indicates a strong unsupported Rh - Rh single bond. Due to the axial coordination of py the Rh atoms are virtually bonded in the centre ( ct ) of the pc 2− core (d( Rh - ct ) = 0.08(1) Å). The pc 2− ligands are staggered with the skew angle φ( N iso - Rh - Rh '- N iso ') = 42(1)°. Asymmetrical doming of the pc 2− ligands is caused by a short interplanar distance (d( ct - ct ) = 2.89(1) Å) and axial coordination of pyridine. Due to the labilizing trans influence of the Rh - Rh bond the d( Rh - N py ) = 2.309(8) Å is rather long. Two quasi-reversible anodic and four cathodic electron transfer processes are observed in the differential pulse voltammogram of [{ Rh ( py ) pc 2−}2] at 0.81, 0.55, −0.33, −0.50, −0.75 and −1.33 V. The UV/vis NIR spectrum of [{ Rh ( py ) pc 2−}2] shows the typical π-π* transitions of the pc 2− ligand. The B region is split into two bands at 15 440 ( B −) and 16 890 cm−1( B +) of equal intensity due to strong excitonic coupling. The totally symmetric Rh - Rh stretching vibration is selectively enhanced in the Fourier Transform–Raman spectrum at 176 cm−1.