You can convert cartesian coordinate to z-matrix using proper programs (gaussview, avogadro. etc). Also, you can directly make z-matrix by your hands.

If you want to use ecp potential with split valence basis set, you should use gen keyword and read or genecp.

Moreover, you should mention the pseudo potential in the end of input file.

Here i give you examples about AuSCH2CH3 ligand using genECP keyword and gen keyword.

%chk=a

%mem=10GB

%nproc=8

#p B3LYP/genECP opt scf

a

0 1

Au -2.70372894 2.50382579 0.32959385

S -4.88184487 1.68548668 0.00000000

C -6.03230723 3.04373421 0.00000000

C -7.44604634 2.54164676 0.00000000

H -5.83457979 3.66826249 -0.90492200

H -5.83453925 3.66832464 0.90486300

H -8.16836197 3.39372340 0.00006000

H -7.64341096 1.91703510 -0.90497800

H -7.64340048 1.91695181 0.90492100

C H S (you should define atoms that is involved in molecule)

6-31G* (define basis set for C, H, S atom)

****

Au 0

LANL2DZ

****

Au 0

LANL2DZ

----------------------------------------------------------------------------------------------------------------

%chk=a

%mem=10GB

%nproc=8

#p B3LYP/gen pseudo=read opt scf

a

0 1

Au -2.70372894 2.50382579 0.32959385

S -4.88184487 1.68548668 0.00000000

C -6.03230723 3.04373421 0.00000000

C -7.44604634 2.54164676 0.00000000

H -5.83457979 3.66826249 -0.90492200

H -5.83453925 3.66832464 0.90486300

H -8.16836197 3.39372340 0.00006000

H -7.64341096 1.91703510 -0.90497800

H -7.64340048 1.91695181 0.90492100

C H S (you should define atoms that is involved in molecule)

6-31G* (define basis set for C, H, S atom)

****

Au 0

S 3 1.00

2.8090000 -1.2021556

1.5950000 1.6741578

0.5327000 0.3526593

S 4 1.00

2.8090000 1.1608481

1.5950000 -1.8642846

0.5327000 -1.0356230

0.2826000 1.3064399

S 1 1.00

0.0598000 1.0000000

P 3 1.00

3.6840000 -0.2802681

1.6660000 0.7818398

0.5989000 0.4804776

P 2 1.00

0.6838000 -0.0952078

0.0977000 1.0299147

P 1 1.00

0.0279000 1.0000000

D 2 1.00

1.2870000 0.5844273

0.4335000 0.5298161

D 1 1.00

0.1396000 1.0000000

****

AU 0

AU-ECP 4 60

g-ul potential

5

1 622.6287956 -60.0000000

2 136.2843607 -555.5292312

2 33.1549781 -168.0019785

2 9.9894895 -63.0399875

2 3.0481312 -4.2516681

s-ul potential

6

0 194.7374304 3.0000000

1 351.5327447 38.6020880

2 122.3270402 864.8370727

2 32.0914617 374.9935520

2 5.2451812 289.7910100

2 4.4916223 -152.4532773

p-ul potential

4

0 420.6158801 2.0000000

1 109.4417815 73.8885625

2 34.1714280 326.6729872

2 5.9879750 126.5814591

d-ul potential

5

0 219.2666158 3.0000000

1 122.7297786 55.6793149

2 63.1063369 449.1987335

2 18.3684520 215.0269091

2 4.4972844 64.0840995

f-ul potential

5

0 108.5506037 4.0000000

1 56.4795527 51.8065335

2 29.2069159 231.2183113

2 9.5440543 119.0047386

2 2.8965118 15.3424188

Thank you very much Mr.Subankar

Thank you Mr. Sunwoo Kang for very detailed explanation