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Preparation, Properties, and Crystal Structure of Quaternary Silicide Carbides RCr2Si2C (R = Y, La - Nd, Sm, Gd - Ho)

The title compounds were prepared by arc-melting cold-pressed pellets of the elemental components. They crystallize with a tetragonal structure already reported for CeCr2Si2C. It was refined from single-crystal X-ray data of PrCr2S2C: P4/mmm, a - 402.2( 1) pm, c = 535.2(1) pm, Z = 1, R = 0.012 for 252 structure factors and 10 variable parameters. Magnetic susceptibility measurements with a SQUID magnetometer indicate Pauli paramagnetism for YCr2Si2C, while CeC2Si2C shows mixed valent behavior. The carbon atoms in the structure of these compounds are isolated from each other. The silicon atoms form pairs with a Si-Si distance of 245.3 pm, somewhat greater than the single-bond distance of 235.2 pm in elemental silicon. Together with the chromium atoms, the silicon pairs and carbon atoms form a three-dimensionally infinite polyanion, which has some similarity with the polyanions found in several related tetragonal structures, e.g., the structures of ThCr2Si2 and LuNi2B2C.