Tricarbonylchromium complexes of centropolyindans. Part4. Physicochemical and structural characterization ofanti-Cr(CO)3-4b,9,9a,10-tetrahydroindeno[1,2-a]indene,syn-Cr(CO)3-4b,9,9a,10-tetrahydroindeno[1,2-a]indene andsyn,anti-[Cr(CO)3]2-4b,9,9a,10-tetrahydroindeno[1,2-a]indene