Tetrasubstituted methanes having liquid-crystalline properties

A methane derivative of the general formula

• C[--Sp--M--R].sub.4 (I)
• in which the radicals --Sp--M--R can be identical or different and where
• Sp is, in each case independently of the other cases, is an alkylene or alkenylene radical having up to 12 carbon atoms which is unsubstituted or monosubstituted by halogen, --CN or --CF.sub.3 and in which, in addition, one or two non-adjacent CH.sub.2 groups can be replaced by --O--, --CO--, --COO--, --OOC--, --CONH-- or --OCOO--, or is a single bond;
• M is a mesogenic group of the general formula --A--(Z.sub.1 --A.sub.1).sub.m --(Z.sub.2 --A.sub.2).sub.n -- in which
• Z.sub.1 and Z.sub.2 are each, independently of one another, --CH.sub.2 CH.sub.2 --, --COO--, --OOC--, --OCH.sub.2 --, CH.sub.2 O--, --C.tbd.C--, --N.dbd.N-- or a single bond;
• A, A.sub.1 and A.sub.2 are each, independently of one another, a 1,4- phenylene radical which is unsubstituted or monosubstituted to tetrasubstituted by fluorine or chlorine and in which, in addition, one or two CH groups can be replaced by N, or are a 1,4-cyclohexylene radical which has, in particular, a trans-configuration and in which, in addition, one or two non-adjacent CH.sub.2 groups can be replaced by --O--, or are a piperidine-1,4-diyl radical or a 1,4-bicyclo[2.2.2]octylene radical;
• and
• n and m are each, independently of one another, 0 or 1, with the proviso that m or n is 1 at least once in one of the four substituents of the methane;
• and
• R is hydrogen, halogen, --CN, --CF.sub.3, --OCF.sub.3, --NO.sub.2, --N(CH.sub.3).sub.2, a straight-chain or branched alkyl or alkenyl radical having up to 12 carbon atoms which is unsubstituted or monosubstituted or polysubstituted by --CN, --NH.sub.2, --CF.sub.3 or haloogen and in which one or more non-adjacent CH.sub.2 groups can be replaced by the radicals --O--, --CO--, --COO--, --OOC-- or --OCOO--.